WO1991019780A1

WO1991019780A1 - Protein removal using precipitated silica

Info

Publication number: WO1991019780A1
Application number: PCT/US1991/002858
Authority: WO
Inventors: Timothy A. Okel
Original assignee: Ppg Industries, Inc.
Priority date: 1990-06-21
Filing date: 1991-04-25
Publication date: 1991-12-26

Abstract

A liquid medium in which protein is dissolved, suspended, or dispersed is contacted with amorphous precipitated silica having, on a coating-free and impregnant-free basis, a surface area of from about 190 to about 600 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 7 to about 30 nanometers and/or an average pore diameter by nitrogen adsorption of from about 3 to about 19 nanometers, and a total intruded volume of from about 2.3 to about 5 cubic centimeters per gram, whereby at least a portion of the protein is adsorbed by the amorphous precipitated silica. The process is particularly suitable for chillproofing beer.

Description

PROTEIN REMOVAL USING PRECIPITATED SILICA The present invention provides a process for removing protein from a liquid medium in which protein is dissolved, suspended, or dispersed. It is particularly applicable for the removal of undesirable proteins from beverages such as beer, wine, distilled spirits, fruit juice, vegetable juice, and the like. In the preferred embodiment, the process is employed for the chillproofing of beer. The term "beer" as used in the present specification and claims is a brewed fermentation product produced from malted cereal grains (usually the chief cereal grain is barley) and hops as the main starting materials and includes many types of brewed beverages. Such beverages include, but are not limited to, lager, pilsner, Dortmund and Munich beers, as well as top fermented beverages such as ale, porter, and stout. Although the details may vary somewhat from brewery to brewery, a generally representative procedure for making beer is as follows: (1) Ground malt (grist) is placed in a mash tun for saccharification together with water, and while the temperature is gradually raised from about 5-55°C to about 75-80°C over a period of from about 2 to about 3 hours, starch in the malt is decomposed into sugars such as maltose, dextrin, and the like; (2) The resulting mash after saccharification is filtered to obtain a clear malt'liquor (wort); (3) Hops are added to the filtered malt liquor and boiled for about an hour or two; (4) The hot wort is transferred to a precipitation tank and, after removing hot coagulates, cooled to 5-10°C; (5) Yeast is added to the cooled wort, and oxygen is supplied to promote the growth of the yeast; (6) Fermentation is effected at temperatures of about 10°C for about a week (primary fermentation); (7) Secondary fermentation and aging of the resulting beer are effected in a storage tank at low temperatures of about nT for one to two months; (8) The beer is then filtered and packed into containers (usually bottles, cans, or barrels).

In terms of volume, by far the greatest amount of beer produced is light-colored. An amber-colored, bright, and transparent appearance is one of the great product characteristics of light-colored beer. If, however, the stability of beer is not adequate, a cloudiness known as haze can develop when the beer is stored for a prolonged time after packing into containers or when cooled. Such haze is undesirable since it is often perceived by consumers as the result of product deterioration.

Haze is generally classified into three types: (1) "chill haze", which is brought about when beer is cooled to about 0°C but solubilized again when wanned to about 20^βC; (2) "permanent (or oxidized) haze", which is no longer solubilized even when the beer is warmed to 20°C; and (3) "frozen haze", which is brought about when beer is frozen or stored at temperatures near the freezing point of about -5°C. Of these, the type of primary concern is chill haze.

Chill haze is formed by the complexation of proteins with tannins or polyphenols. Various materials known as "chillproofing agents", "clarifiers", or "stabilizers" have been employed to remove chill haze or, more often, chill haze precursors. These are categorized as (1) those which break down the haze-forming proteins, e.g., enzymes such as proteases and papain; (2) those which remove the tannins and/or polyphenols, e.g., tannic acid, polyamides, and crosslinked polyvinylpolypyrrolidone; and (3) those which adsorb the haze forming proteins, e.g., swelling clays, porous glass, and various other siliceous materials. Combinations of such materials from the same category or from differing categories have also been employed.

Wort nitrogen can be separated into four classes. Haze instability is reported to be caused by the acidic protein-tannin complexes of high molecular weight (over 60,000) and is directly related to malt content. This is about 2 percent or less of wort nitrogen and is referred to as "Lundin Fraction A." Beer foam, which is a desirable characteristic, is produced by neutral proteins over 12,000 molecular weight associated with carbohydrates and hop bitter substances. These proteins constitute from about 2 percent to about A percent of wort nitrogen and are known as "Lundin Fraction B." The haze forming proteins themselves are reportedly smaller than the foam proteins. The lower molecular weight components, known as "Lundin Fraction C" are further subdivided into those which affect flavor (greater than about 10 and less than about 100 a ino acid units) and those utilized by yeast (about 5 to about 10 amino acid units). Activated carbon and swelling clays such as bentonite adsorb all three Lundin Fractions. Bentonite, in addition to causing deleterious effects on foam and flavor, requires a lengthy cold storage period for settling. Enzymes have a negative impact on foam. Tannic acid has been found to preferentially precipitate the haze forming fraction without affecting foam and flavor. However, a large amount of precipitate is produced which settles to the bottom of the storage tank. The high cost of handling this precipitate and the accompanying large loss of beer are major drawbacks to the use of tannic acid. A considerable advance in the art was the discovery of certain silica gels which preferentially adsorb the haze forming protein fraction. These silica gels are characterized by a narrow pore size distribution around a desired pore diameter. Precipitated silica has been suggested for use as a chillproofing agent. United States Patent No. 3,480,390 discloses the use of precipitated silica as a chillproofing agent in which the properties of the precipitated silica are a surface area of at least 400 m^z/g and pore diameter of at least 6 nanometers. United States Patent No. 3,554,759 discloses use of precipitated silica in the presence of water soluble polyvinyl pyrrolidone or its water soluble derivatives. European Patent Application Publication No. 0 287 232 discloses such use in which the properties of the precipitated silica are a surface area of from 450 to 1100 m /g, pore diameters of from 8 to 20 nanometers, pore volumes of from 1.6 to 2.5 mL/g, particle sizes of from 5 to 30 micrometers, and a moisture content of less than 25 percent by weight. It has now been found that amorphous precipitated silicas which are characterized by certain surface areas, pore diameters, and pore volumes are very effective chillproofing agents. These amorphous precipitated silicas are usually at least about as efficient as silica gel chillproofers in current commercial use. In many cases these amorphous precipitated silicas are more efficient than silica gels in that one can use a lesser quantity of the amorphous precipitated silica than silica gel to achieve a given haze reduction under standard conditions. Accordingly, in a process wherein a liquid medium in which protein is dissolved, suspended, or dispersed is contacted with amorphous precipitated silica and wherein at least a portion of the protein is adsorbed by the amorphous precipitated silica, one embodiment of the invention is the improvement wherein the amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 190 to about 600 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 7 to about 30 nanometers, and a total intruded volume of from about 2.3 to about 5 cubic centimeters per gram.

Similarly, in a process wherein a liquid medium in which protein is dissolved, suspended, or dispersed is contacted with amorphous precipitated silica and wherein at least a portion of the protein is adsorbed by the amorphous precipitated silica, another embodiment of the invention is the improvement wherein the amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 190 to about 600 square meters per gram, an average pore diameter by nitrogen adsorption of from about 3 to about 19 nanometers, and a total intruded volume of from about 2.3 to about 5 cubic centimeters per gram.

Many different amorphous precipitated silicas are known and have been used in a wide variety of applications. Precipitated silicas are most commonly produced by precipitation from an aqueous solution of sodium silicate using a suitable acid such as sulfuric acid, hydrochloric acid, and/or carbon dioxide. Processes for producing precipitated silicas are described in detail in United States Patents No. 2,657,149; 2,940,830; and 4,681,750, the entire disclosures of which are incorporated herein by reference, including especially the processes for making precipitated silicas and the properties of the products. These prior precipitated silicas, however, did not possess the combination of properties as would render them efficient chillproofing agents.

Although both are silicas, it is important to distinguish precipitated silica from silica gel inasmuch as these different materials have different properties. Reference in this regard is made to R. K. Her, The Chemistry of Silica_τ John Wiley & Sons, New York (1979), Library of Congress Catalog No. QD 181.S6144. Note especially pages 15-29, 172-176, 218-233, 364-365, 462-465, 554-564, and 578-579, the entire disclosures of which are incorporated herein by reference. Silica gel is usually produced commercially at low pH by acidifying an aqueous solution of a soluble metal silicate, customarily sodium silicate, with acid. The acid employed is generally a strong mineral acid such as sulfuric acid or hydrochloric acid although carbon dioxide is sometimes used.

Inasmuch as there is essentially no difference in density between the gel phase and the surrounding liquid phase while the viscosity is low, the gel phase does not settle out, that is to say, it does not precipitate. Silica gel, then, may be described as a non-precipitated, coherent, rigid, three-dimensional network of contiguous particles of colloidal amorphous silica. The state of subdivision ranges from large, solid masses to submicroscopic particles, and the degree of hydration from almost anhydrous silica to soft gelatinous masses containing on the order of 100 parts of water per part of silica by weight, although the highly hydrated forms are only rarely used.

Precipitated silica is usually produced commercially by combining an aqueous solution of a soluble metal silicate, ordinarily alkali metal silicate such as sodium silicate, and an acid so that colloidal particles will grow in weakly alkaline solution and be coagulated by the alkali metal ions of the resulting soluble alkali metal salt. Various acids may be used, including the mineral acids and/or carbon dioxide. In the absence of a coagulant, silica is not precipitated from solution at any pH. The coagulant used to effect precipitation may be the soluble alkali metal salt produced during formation of the colloidal silica particles, it may be added electrolyte such as a soluble inorganic or organic salt, or it may be a combination of both.

Precipitated silica, then, may be described as precipitated aggregates of ultimate particles of colloidal amorphous silica that have not at any point existed as macroscopic gel during the preparation. The sizes of the aggregates and the degree of hydration may vary widely.

Precipitated silica powders differ from silica gels that have been pulverized in ordinarily having a more open structure, that is, a higher specific pore volume. However, the specific surface area of precipitated silica as measured by the Brunauer, Emmett, Teller (BET) method using nitrogen as the adsorbate, is often lower than that of silica gel. Variations in the parameters and/or conditions during production result in variations in the types of precipitated silicas produced. Although they are all broadly precipitated silicas, the types of precipitated silicas often differ significantly in physical properties and sometimes in chemical properties. These differences in properties are important and often result in one type being especially useful for a particular purpose but of marginal utility for another purpose, whereas another type is quite useful for that other purpose but only marginally useful for the first purpose.

The preferred amorphous precipitated silicas for use in the present invention are reinforced amorphous precipitated silicas. Reinforcement of precipitated silica, that is, the deposition of silica on aggregates of previously precipitated silica, is itself known. It has now been found, however, that by controlling the conditions of silica precipitation and multiple reinforcement steps, 5 new silicas may be produced having properties that make them especially useful for clarifying beer.

Although it is not desired to be bound by any theory, it is believed that as precipitated silica is dried, the material shrinks; consequently, pore diameters are reduced, surface area is reduced, 10 and the void volume is reduced. It is further believed that by sufficiently reinforcing the silica prior to drying, a more open structure is obtained after drying. Irrespective of theory and irrespective of whether or not it is reinforced, the amorphous precipitated silica used in the present invention has, on balance, 15 larger pore diameters and a larger total intruded volume for the surface area obtained than is the case for precipitated silicas previously used for adsorption of proteins.

A class of amorphous precipitated silica having, on a coating-free and impregnant-free basis, a surface area of from about

20 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 9 to about 20 nanometers, and a total intruded volume of from about 2.6 to about 4.4 cubic centimeters per gram and which may be used in the present invention may be produced by the process comprising:

25 (a) establishing an initial aqueous alkali metal silicate solution containing from about 0.5 to about 4 weight percent Si0 and having an molar ratio of from about 1.6 to about 3.9; (b) over a period of at least about 20 minutes and with agitation, adding acid to the initial aqueous alkali metal silicate solution at a 0 temperature below about 50°C to neutralize at least about 60 percent of the MoO present in the initial aqueous alkali metal solution and thereby to form a first reaction mixture; (c) over a period of from about 115 to about 240 minutes, with agitation, and at a temperature of from about 80°C to about 95°C, substantially simultaneously 5 adding to the first reaction mixture: (1) additive aqueous alkali metal silicate solution, and (2) acid, thereby to form a second reaction mixture wherein the amount of the additive aqueous alkali metal silicate solution added is such that the amount of Siθ2 added is from about 0.5 to about 2 times the amount of SiO present in the initial aqueous alkali metal silicate solution established in step (a) and wherein the amount of the acid added is such that at least about 60 percent of the M θ contained in the additive aqueous alkali metal silicate solution added during the simultaneous addition is neutralized; (d) adding acid to the second reaction mixture with agitation at a temperature of from about 80^βG to about 95^βC to form a third reaction mixture having a pH below 7; (e) aging the third reaction mixture with agitation at a pH below 7 and at a temperature of from about 80°C to about 95°C for a period of from about 1 to about 120 minutes; (f) with agitation and at a temperature of from about 80°C to about 95°C, adding to the aged third reaction mixture additive aqueous alkali metal silicate solution to form a fourth reaction mixture having a pH of from about 7.5 to about 9; (g) forming a fifth reaction mixture by adding to the fourth reaction mixture with agitation and at a temperature of from about 80^βC to about 95°C, a further quantity of additive aqueous alkali metal silicate solution and adding acid as necessary to maintain the pH at from about 7.5 to about 9 during the addition of the further quantity of the additive aqueous alkali metal silicate solution, wherein: (1) the amount of the additive aqueous alkali metal silicate solution added in steps (f) and (g) is such that the amount of SiU2 added in steps (f) and (g) is from about 0.05 to about 0.75 times the amount of Siθ2 present in the third reaction mixture, and (2) the additive aqueous alkali metal silicate solution is added in steps (f) and (g) over a collective period of at least about 40 minutes; (h) aging the fifth reaction mixture with agitation at a temperature of from about 80°C to about 95°C for a period of from about 5 to about 60 minutes; (i) adding acid to the aged fifth reaction mixture with agitation at a temperature of from about 80°C to about 95°C to form a sixth reaction mixture having a pH below 7; (j) aging the sixth reaction mixture with agitation at a pH below 7 and at a temperature of from about 80°C to about 95°C for a period of at least about 1 minute; (k) separating precipitated silica from most of the liquid of the aged sixth reaction mixture; (1) washing the separated precipitated silica with water; and (m) drying the washed precipitated silica, wherein: (n) the alkali metal silicate is lithium silicate, sodium silicate, potassium silicate, or a mixture thereof; and (o) M is lithium, sodium, potassium, or a mixture thereof.

Optionally, prior to step (c) the first reaction mixture is aged with agitation at a temperature of from about 30^βC to about 95°C for a period of from about 5 to about 180 minutes.

The composition of the initial aqueous alkali metal silicate solution established in step (a) may vary widely. Generally the initial aqueous alkali metal silicate solution comprises from about 0.5 to about 4 weight percent Siθ2< In many cases the initial aqueous alkali metal silicate solution comprises from about 1 to about 3 weight percent Siθ « From about 1.5 to about 2.5 weight percent Si0₂ is preferred. Usually the initial aqueous alkali metal silicate solution has an Siθ2:M2θ molar ratio of from about 1.6 to about 3.9. Often the Siθ2ϊ_"-2θ molar ratio is from about 2.5 to about 3.6. Preferably the Siθ2ϊM2θ molar ratio is from about 2.9 to about 3.6. Often the Siθ2S-*_2θ molar ratio is from about 3.2 to about 3.3.

The composition of the additive aqueous alkali metal silicate solution may also vary widely. Usually the additive aqueous alkali metal silicate solution comprises from about 2 to about 30 percent by weight Siθ2« Often the additive aqueous alkali metal silicate solution comprises from about 10 to about 15 percent by weight Siθ2> From about 12 to about 13 weight percent Si0₂ is preferred. Frequently the additive aqueous alkali metal silicate solution has an Si0₂ M₂0 molar ratio of from about 1.6 to about 3.9. In many cases the Si02:M2θ molar ratio is from about 2.5 to about 3.6. Preferably the Siθ2 M2θ molar ratio is from about 2.9 to about 3.6. Often the Si0₂:M2θ molar ratio is from about 3.2 to about 3.3. Additive aqueous alkali metal silicate solution having the same composition may be used throughout the various silicate additions, or additive aqueous alkali metal silicate solutions having differing compositions may be used in different silicate addition steps. The acid used in the process may also vary widely. In general, the acid added in steps (b), (c), and (g) should be strong enough to neutralize alkali metal silicate and cause precipitation of silica. The acid added in steps (d) and (i) should be strong enough to reduce the pH to desired values within the specified ranges. The acid used in the various acid addition steps may be the same or different, but preferably it is the same. A weak acid such as carbonic acid produced by the introduction of carbon dioxide to the reaction mixture may be used for precipitation of silica, but a stronger acid must be used in steps (d) and (i) when it is desired to reduce the pH to values below 7. It is preferred to use strong acid throughout the process. Examples of the strong acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and acetic acid. The strong mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid are preferred; sulfuric acid is especially preferred.

The acid addition of step (b) is made over a period of at least about 20 minutes. Frequently the acid addition of step (b) is made over a period of from about 20 to about 60 minutes. From about 26 to about 32 minutes is preferred. The temperature of the reaction mixture during the acid addition of step (b) is below about 50°C. From about 30°C to about 40°C is preferred.

At least about 60 percent of the 2O present in the initial aqueous alkali metal silicate solution is neutralized during the acid addition of step (b). As much as 100 percent of the M₂0 may be neutralized if desired. Preferably from about 75 to about 85 percent of the M2O is neutralized.

The additions made in step (c) are made over a period of from about 115 to about 240 minutes. Preferably the additions are made over a period of from about 115 to about 125 minutes. The temperature of the reaction mixture during the additions of step (c) is from about 80°C to about 95°C. From about 90°C to about 95°C is preferred.

In step (c), the amount of additive aqueous alkali metal silicate added is such that the amount of Siθ2 added is from about 0.5 to about 2 times the amount of Siθ2 present in the initial aqueous alkali metal silicate solution established in step (a). From about 0.9 to about 1.1 times the Siθ2 present in the initial aqueous alkali metal silicate solution is preferred. The amount of acid added in step (c) is such that at least about 60 percent of the M2O contained in the additive aqueous alkali metal silicate solution added in step (c) is neutralized. As much as 100 percent of such M2O may be neutralized if desired. Preferably from about 75 to about 85 percent of the M2O is neutralized.

The temperature of the reaction mixture during the acid addition of step (d) is from about 80°C to about 95°C. From about 90°C to about 95^βC is preferred.

In step (d), the acid is added such that the pH of the third reaction mixture is below 7. Often the pH is from about 2.5 to below 7. A pH of from about 4 to about 5 is preferred.

Similarly, the third reaction mixture is aged in step (e) at a'pH below 7. Often the pH is from about 2.5 to below 7. A pH of from about 4 to about 5 is preferred. The temperature of the third reaction mixture during the aging of step (e) is from about 80°C to about 95°C. From about 90^βC to about 95°C is preferred.

The aging in step (e) is for a period of from about 1 to about 120 minutes. In many cases the third reaction mixture is aged for a period of from about 15 to about 120 minutes. A period of from about 15 to about 30 minutes is preferred.

The temperature of the reaction mixture during the addition of additive aqueous alkali metal silicate solution in step (f) is from about 80^βC to about 95°C. From about 90°C to about 95°C is preferred. The pH of the fourth reaction mixture formed in step (f) is from about 7.5 to about 9. A pH of from about 8 to about 9 is preferred.

Acid is added in step (g) as necessary to maintain the pH 5 of the reaction mixture at from about 7.5 to about 9 during the addition of the further quantity of additive aqueous alkali metal silicate solution. A pH of from about 8 to about 9 is preferred.

The amount of additive aqueous alkali metal silicate solution added in steps (f) and (g) is such that the amount of SiU2 10 added in steps (f) and (g) is from about 0.05 to about 0.75 times the amount of Siθ2 present in the third reaction mixture. Preferably the amount of additive aqueous alkali metal silicate solution added in steps (f) and (g) is such that the amount of Siθ2 added in steps (f) and (g) is from about 0.25 to about 0.45 times 15 the amount of Siθ2 present in the third reaction mixture.

The additive alkali metal silicate solution is added in steps (f) and (g) over a collective period of at least about 40 minutes. A collective period of from about 40 to about 240 minutes is often employed. A collective period of from about 70 to about 20 100 minutes is preferred.

The temperature of the fifth reaction mixture during the aging of step (h) is from about 80°C to about 95°C. From about 90°C to about 95°C is preferred.

In step (h), the fifth reaction mixture is aged for a 25 period of from about 5 to about 60 minutes. A period of from about 30 to about 60 minutes is preferred.

The temperature of the reaction mixture during the acid addition of step (i) is from about 80°C to about 95°C. From about 90°C to about 95°C is preferred. 30 In step (i), the acid is added such that the pH of the sixth reaction mixture is below 7. Often the pH is from about 2.5 to below 7. A pH of from about 4 to about 5 is preferred.

The sixth reaction mixture is aged in step (j) at a pH below 7. In many cases the pH is from about 2.5 to below 7. A pH 35 of from about 4 to about 5 is preferred. The temperature of the sixth reaction mixture during the aging of step (j) is from about 80°C to about 95°C. From about 90°C to about 95°C is preferred.

In step (j), the sixth reaction mixture is aged for a 5 period of at least about 1 minute. Often the aging period is at least about 30 minutes. An aging period of at least about 50 minutes is preferred.

The separation of step (k) may be accomplished by one or more techniques for separating solids from liquid such as, for 10 example, filtration, centrifugation, decantation, and the like.

The washing of step (1) may be accomplished by any of the procedures known to the art for washing solids. Examples of such procedures include passing water through a filter cake, and reslurring the precipitated silica in water followed by separating 15 the solids from the liquid. One washing cycle or a succession of washing cycles may be employed as desired. The primary purpose of washing is to remove salt formed by the various neutralizations to desirably low levels. Usually the precipitated silica is washed until the concentration of salt in the dried precipitated silica is 20 less than or equal to about 2 percent by weight. Preferably the precipitated silica is washed until the concentration of salt is less than or equal to about 0.2 percent by weight.

The drying of step (m) may also be accomplished by one or more known techniques. For example, the precipitated silica may be 25 dried in an air oven or in a vacuum oven. Preferably the precipitated silica is dispersed in water and spray dried in a column of hot air. The temperature at which drying is accomplished is not critical, but the usual practice is to employ temperatures of at least 70°C. Generally the drying temperature is less than about 30 700°C. In most cases drying is continued until the precipitated silica has the characteristics of a powder. Ordinarily the dried precipitated silica is not absolutely anhydrous but contains bound water (from about 2 to about 5 weight percent) and adsorbed water (from about 1 to about 7 weight percent) in varying amounts, the 5 latter depending partly upon the prevailing relative humidity. Adsorbed water is that water which is removed from the silica by heating at 105°C for 24 hours at atmospheric pressure in a laboratory oven. Bound water is that water which is removed by additionally heating the silica at calcination temperatures, for example, from about 1000°C to about 1200°C.

Another optional step which may be employed is size reduction. Size reduction techniques are themselves well known and may be exemplified by grinding and pulverising. Particularly preferred is fluid energy milling using air or superheated steam as the working fluid.

Fluid energy mills are themselves well known. See, for example, Perry's Chemical Engineers' Handbook. 4th Edition McGraw-Hill Book Company, New York, (1963), Library of Congress Catalog Card Number 6113168, pages 8-42 and 8-43; McCabe and Smith, Unit Operations of Chemical Engineering,, 3rd Edition, McGraw-Hill Book Company, New York (1976), ISBN 0-07-044825-6, pages 844 and 845; F. E. Albus, "The Modern Fluid Energy Mill", Chemical Engineering Progress. Volume 60, No. 6 (June 1964), pages 102-106, the entire disclosures of which are incorporated herein by reference. In fluid energy mills the solid particles are suspended in a gas stream and conveyed at high velocity in a circular or elliptical path. Some reduction occurs when the particles strike or rub against the walls of the confining chamber, but most of the reduction is believed to be caused by interparticle attrition. The degrees of agitation used in the various steps of the invention may vary considerably. The agitation employed during the addition of one or more reactants should be at least sufficient to provide a thorough dispersion of the reactants and reaction mixture so as to avoid more than trivial locally high concentrations of reactants and to ensure that silica deposition occurs substantially uniformly thereby avoiding gellation on the macro scale. The agitation employed during aging should be at least sufficient to avoid settling of solids to ensure that silica deposition occurs substantially uniformly throughout the mass of silica particles rather than preferentially on those particles at or near the top of a settled layer of particles. The degrees of agitation may, and preferably are, greater than these minimums. In general, vigorous agitation is preferred.

A preferred process for producing amorphous precipitated silica 5 having, on a coating-free and impregnant-free basis, a surface area of from about 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 13 to about 18 nanometers, and a total intruded volume of from about 3 to about 4.4 cubic centimeters per 10 gram, is the process comprising: (a) establishing an initial aqueous alkali metal silicate solution containing from about 0.5 to about 4 weight percent Siθ2 and having an Siθ2:M2^υ mol r ratio of from about 1.6 to about 3.9; (b) over a period of at least about 20 minutes and with agitation, adding acid to the initial aqueous 15 alkali metal silicate solution at a temperature of from about 30°C to about 40°C to neutralize from about 75 to about 85 percent of the M2O present in the initial aqueous alkali metal solution and to form a first reaction mixture; (c) over a period of from about 115 to about 125 minutes, with agitation, and at a temperature of from 20 about 90°C to about 95^βC, substantially simultaneously adding to the first reaction mixture: (1) additive aqueous alkali metal silicate solution, and (2) acid, to form a second reaction mixture wherein the amount of the additive aqueous alkali metal silicate solution added is such that the amount of Siθ2 added is from about 0.9 to 25 about 1.1 times the amount of Siθ2 present in the initial aqueous alkali metal silicate solution established in step (a) and wherein the amount of the acid added is such that from about 75 to about 85 percent of the M2O contained in the additive aqueous alkali metal silicate solution added during the simultaneous addition is 30 neutralized; (d) adding acid to the second reaction mixture with agitation at a temperature of from about 90°C to about 95°C to form a third reaction mixture having a pH of from about 4 to about 5; (e) aging the third reaction mixture with agitation at a temperature of from about 90^βC to about 95°C for a period of from about 15 to about 35 30 minutes; (f) With agitation and at a temperature of from about 90°C to about 95°C, adding to the aged third reaction mixture additive aqueous alkali metal silicate solution to form a fourth reaction mixture having a pH of from about 8 to about 9; (g) forming a fifth reaction mixture by adding to the fourth reaction mixture with agitation and at a temperature of from about 90^βC to about 95°C, a further quantity of additive aqueous alkali metal silicate solution and adding acid as necessary to maintain the pH at from about 8 to about 9 during the addition of the further quantity of the additive aqueous alkali metal silicate solution, wherein: (1) the amount of the additive aqueous alkali metal silicate solution added in steps (f) and (g) is such that the amount of SiU2 added in steps (f) and (g) is from about 0.25 to about 0.45 times the amount of Siθ2 present in the third reaction mixture, and (2) the additive aqueous alkali metal silicate solution is added in steps (f) and (g) over a collective period of from about 70 to about 100 minutes; (h) aging the fifth reaction mixture with agitation at a temperature of from about 90°C to about 95^βC for a period of from about 30 to about 60 minutes; (i) adding acid to the aged fifth reaction mixture with agitation at a temperature of from about 90^CC to about 95°C to form a sixth reaction mixture having a pH of from about 4 to about 5; (j) aging the sixth reaction mixture with agitation at a temperature of from about 90°C to about 95°C for a period of at least about 50 minutes; (k) separating precipitated silica from most of the liquid of the aged sixth reaction mixture; (1) washing the separated precipitated silica with water; and (m) drying the washed precipitated silica, wherein: (n) the alkali metal silicate is lithium silicate, sodium silicate, potassium silicate, or a mixture thereof; and (o) M is lithium, sodium, potassium, or a mixture thereof. It is understood that one or more ranges in the preferred process may be used in lieu of the corresponding broader range or ranges in the broader process.

There are several commercially available amorphous precipitated silicas which may be used in the present invention. Included among these are Flo-Gard® SP precipitated silica (PPG Industries, Inc.) for which the surface area is from about 200 to about 220 m /g, the pore diameter at the maximum of the volume pore size distribution function is from about 26 to about 27 nm, and the total intruded volume is from about 2.9 to about 3.5 cc/g; Hi-Sil® 5 132 precipitated silica (PPG Industries, Inc.) for which the surface r, area is from about 190 to about 193 m /g, the pore diameter at the maximum of the volume pore size distribution function is from about 22 to about 24 nm, and the total intruded volume is approximately 2.4 cc/g; Sipernat® 50 precipitated silica (Degussa Aktiengesellschaft; see United States Patent No. 4,495,167) for which the surface area is from about 490 to about 600 m /g, the pore diameter at the maximum of the volume pore size distribution function is less than 7 nm by mercury porosimetry but the average pore diameter by nitrogen adsorption is about 13 nm, and the total intruded volume is from about 2.5 to about 3.1 cc/g. The disclosure of United States Patent No. 4,495,167 is, in its entirety, incorporated herein by reference.

As used in the present specification and claims, the surface area of the amorphous precipitated silica used in the present invention is the surface area determined by the Brunauer, Emmett, Teller (BET) method according to ASTM C 819-77 using nitrogen as the adsorbate but modified by outgassing the system and the sample for one hour at 180°C. The surface area is from about 190 to about 600 square meters per gram. In many cases the surface area is from about 190 to about 340 square meters per gram. From about 220 to about 340 square meters per gram iε preferred. ASTM C 819-77 is, in its entirety, incorporated herein by reference.

The volume average pore size distribution function of the amorphous precipitated silica is determined by mercury porosimetry using an Autoscan mercury porosimeter (Quantachrome Corp.) in accordance with the accompanying operating manual. In operating the porosimeter, a scan is made in the high pressure range (from about 103 kilopascals absolute to about 227 megapascals absolute). The volume pore size distribution function is given by the following equation: d dP where:

D_v(d) is the volume pore size distribution function, usually expressed in cm /(um^*g); d is the pore diameter, usually expressed in μm; P is the pressure, usually expressed in pounds per square inch, absolute; and

V is the pore volume per unit mass, usually expressed in cm³/g.

Dv(d) is determined by taking ΔV/ΔP for small values of ΔP from either a plot of V versus P or preferably from the raw data. Each value of ΔV/ΔP is multiplied by the pressure at the upper end of the interval and divided by the corresponding pore diameter. The resulting value is plotted versus the pore diameter. The value of the pore diameter at the maximum of the volume pore size distribution function is then taken from the plotted graph. Numerical procedures may be used rather than graphical when desired. For one class of reinforced amorphous precipitated silica used in the present invention the pore diameter at the maximum of the volume pore size distribution function is from about 7 to about 30 nanometers. Often the pore diameter at the maximum of the volume pore'size distribution function is from about 13 to about 30 nanometers. In many cases the pore diameter at the maximum of the volume pore size distribution function is from about 9 to about 20 nanometers. Preferably the pore diameter at the maximum of the volume pore size distribution function is from about 13 to about 18 nanometers.

In the course of determining the volume average pore diameter by the above mercury porosimetry procedure, the maximum pore radius detected is sometimes noted. The maximum pore diameter is twice the maximum pore radius.

Pore diameters at the maxima of volume pore size distribution functions smaller than about 6-6 nanometers are not accurately determined by mercury porosimetry. Therefore, average pore diameters for amorphous precipitated silica having on average small but still useful pores are determined by nitrogen adsorption. As used herein and in the claims, average pore diameter by nitrogen adsorption means determining the average pore diameter using a Micromeritics Model 2400 Accelerated Surface Area and Porosimetry Instrument (Micromeritics Instrument Corporation) in accordance with the accompanying operating manual in which the following choices and modifications are followed: (a) samples are prepared by drying for 45 minutes at 180°C, (b) a five point BET Surface Area is selected, (c) a dried sample weight of 0.5 gram is used, (d) a degas temperature of 180^βC is used, (e) total degassing time is 45 ± 5 minutes, (f) the default value in which five partial pressures between 0.05 and 0.2 are selected by the instrument software is chosen, and (g) 15 micropore points and total pore size are selected. The average pore diameter is reported by the instrument. For another class of reinforced amorphous precipitated silica used in the present invention the average pore diameter by nitrogen adsorption is from about 3 to about 19 nanometers. Often the average pore diameter by nitrogen adsorption is from about 6 to about 17 nanometers. Preferably the average pore diameter by nitrogen adsorption is from about 9 to about 14 nanometers.

It should be pointed out that in those regions where the scales of pore diameter of the two methods overlap, the pore diameter determined by the nitrogen adsorption method tends to be larger than that determined by mercury porosimetry.

The total intruded volume is the total volume of mercury which is intruded into the amorphous precipitated silica during the high pressure scan described above divided by the mass of the amorphous precipitated silica constituting the sample under test. The total intruded volume of the amorphous precipitated silica is from about 2.3 to about 5 cubic centimeters per gram. Frequently the total intruded volume of the amorphous precipitated silica is from about 2.6 to about 4.4 cubic centimeters per gram. Preferably the total intruded volume is from about 3 to about 4.4 cubic centimeters per gram. The amorphous precipitated silica may be in the form of aggregates of ultimate particles, agglomerates of aggregates, or a combination of both. The gross particle sizes of the amorphous precipitated silica used in the present invention may vary widely but ordinarily at least about 90 percent by weight of the amorphous precipitated silica has gross particle sizes in the range of from about 1 to about 80 micrometers as determined by use of a Model TAII Coulter counter (Coulter Electronics, Inc.) according to ASTM C 690-80 but modified by stirring the precipitated silica for 10 minutes in Isoton II electrolyte (Curtin Matheson Scientific, Inc.) using a four-blade, 4.5 centimeter diameter propeller stirrer. In many cases at least about 90 percent by weight of the amorphous precipitated silica has gross particle sizes in the range of from about 1 to about 40 micrometers. Often at least about 90 percent by weight of the amorphous precipitated silica has gross particle sizes in the range of from about 5 to about 30 micrometers. Preferably at least about 90 percent by weight of the amorphous precipitated silica has gross particle sizes in the range of from about 10 to about 20 micrometers. Size reduction and/or classification may be used to adjust gross particle sizes as necessary or as desired.

ASTM C 690-80 is, in its entirety, incorporated herein by reference.

The neutralization of alkali metal silicate with acid to produce the amorphous precipitated silica also produces alkali metal salt of the acid(s) used for neutralization as by-product. It is preferred that the amount of such salt associated with the amorphous precipitated silica product be low. When the amorphous precipitated silica is separated from the liquid of the aged sixth reaction mixture, most of the salt is removed with the liquid. Further amounts of salt may conveniently be removed by washing the separated precipitated silica with water. In general, the greater the amount of water used for washing, the lower will be the salt content of the final dried product. It is usually preferred that the amorphous precipitated silica contain less than about 2 percent by weight alkali metal salt. It is preferred that the amorphous precipitated silica contain less than about 1.5 percent by weight alkali metal salt. In order to use the amorphous precipitated silica having the characteristics described above, it is brought into direct contact with the liquid medium. This may be done batchwise or continuously. When the liquid medium is beer, the amorphous precipitated silica is sometimes brought into direct contact with the liquid medium at some point prior to step (7) in the general method for making beer, but usually the amorphous precipitated silica is brought into direct contact with the beer in or between the above-described steps (7) and (8) of the general method for making beer. The contacting operation may be effected, for example, by feeding the precipitated silica into the beer in a storage tank; by feeding the precipitated silica into the beer during the filtration step; by forming a suspension of the precipitated silica in water or beer and feeding the suspension into the beer in a storage tank or during the filtration step or by pumping the beer through a bed of the precipitated silica. When the amorphous precipitated silica is brought into contact with the beer, components causing haze and/or their precursors are adsorbed and removed by the precipitated silica. After the beer or other liquid medium containing proteins has been contacted with the precipitated silica, the precipitated silica is separated from the most of the liquid by any convenient solid-liquid separation procedure known to the art, as for example, decantation, filtration, or centrifugation. The relative proportions of amorphous precipitated silica and the liquid medium which are brought into mutual contact may be widely varied. In general, the relative proportions do not depend upon theory, but on practical considerations such as, for example, the nature and concentration of the proteins to be removed, and the degree of removal desired. There is ordinarily no harm in using amounts of the precipitated silica above that needed to achieve the desired results, except that the use of excessive amounts of precipitated silica usually leads to the loss of excessive amounts of entrained liquid when the precipitated silica and liquid are substantially separated. In the case of beer, the amount of amorphous precipitated silica brought into contact with the beer is ordinarily in the range of from about 50 to about 2000 parts of the precipitated silica per million parts of beer, by weight. From about 50 to about 600 parts of the precipitated silica per million parts of beer by weight is preferred.

The temperatures at which the amorphous precipitated silica and liquid medium are in mutual contact may also be widely varied. The temperatures used do not ordinarily depend on theory, but on practical considerations. In the case of beer, the temperature is usually in the range of from about -2°C to about +30°C. Often the temperature is in the range of from about -2°C to about +20°C. From about -2^βC to about +5°C is preferred.

The contact time of the amorphous precipitated silica and the liquid medium is also susceptible to wide variation and is generally governed by practical considerations rather than theory. For beer, the contact time of the precipitated silica and the beer is usually in the range of from about 30 seconds to about 2 months. A contact time in the range of from about 5 minutes to about 90 minutes is often used. From about 5 minutes to about 30 minutes is preferred.

The invention is further described in conjunction with the following examples which are to be considered illustrative rather than limiting, and in which all parts are parts by weight and all percentages are percentages by weight unless otherwise specified.

EXAMPLE 1 An initial aqueous sodium silicate solution in the amount of 58.881 liters was established in a reactor. The initial aqueous sodium silicate solution contained about 2 weight percent SiO-, anl had an Siθ2:Na2θ molar ratio of about 3.3. The initial aqueous sodium silicate solution was heated to 34^βC and over a period of 28 minutes and with agitation, 26.708 liters of about 2 weight percent aqueous sulfuric acid was added to the initial aqueous alkali metal silicate solution thereby to neutralize about 80 percent of the Na2θ and to form a first reaction mixture. Over a period of 121 minutes, with agitation, and at a temperature of 80°C, a stream of 9.059 liters of additive aqueous sodium silicate solution containing about 13 weight percent Si0₂ and having an Si0₂ Na2θ molar ratio of about 3.3, and a stream of 15.321 liters of about 4 weight percent aqueous sulfuric acid were added simultaneously to the first reaction mixture to form a second reaction mixture. The pH of the second reaction mixture was 9.1. A stream of about 8 liters of about 4 weight percent aqueous sulfuric acid was added to the second reaction mixture with agitation at a temperature of 80^βC to form a third reaction mixture having a pH of 4.5. The third reaction mixture was aged with agitation at 80°C for 30 minutes. The aged third reaction mixture was split into two approximately equal portions. With agitation, 0.45 liter of additive aqueous sodium silicate solution containing about 13 weight percent Siθ2 and having an SiU2:Na2θ molar ratio of about 3.3 was added to one portion of the aged third reaction mixture at 80°C to form a fourth reaction mixture having a pH of 8.5. A fifth reaction mixture was formed by adding to the fourth reaction mixture with agitation and at a temperature of 80^βC, 2.271 liters of additive aqueous sodium silicate solution containing about 13 weight percent Siθ2 and having an SiU2 Na2θ molar ratio of about 3.3 and by adding 5.5 liters of about 4 weight percent aqueous sulfuric acid simultaneously to maintain the pH at about 8.5. The sequential additions to form the fourth and fifth reaction mixtures were made over a collective time period of 43 minutes. The fifth reaction mixture was aged with agitation at 80°C for 45 minutes. With agitation, 1.5 liters of about 4 weight percent aqueous sulfuric acid was added to the aged fifth reaction mixture to form a sixth reaction mixture having a pH of 4.5. The sixth reaction mixture was aged with agitation at 80°C for 60 minutes. The aged sixth reaction mixture was vacuum filtered using a series of Buchner funnels. Just before air could be pulled through each filter cake, the addition of 16 liters of water to the funnel was begun for the purpose of washing the filter cake. Air was briefly pulled through the washed filter^' cake. The wet filter cake contained 9.9 percent solids by weight. After being removed from the funnels, the wet filter cakes were stirred with a propeller type agitator to form a solid in liquid suspension. The suspension was dried in a Niro spray drier (inlet temperature about 360°C; outlet temperature about 128°C) to form a batch of dried reinforced precipitated silica. The product had a surface area of 333 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of 9 nanometers, and a total intruded volume of 3.21 cubic centimeters per gram.

EXAMPLE 2 An initial aqueous sodium silicate solution in the amount of 340.7 liters was established in a reactor. The initial aqueous sodium silicate solution contained about 2 weight percent Si0₂ and had an Si0₂:Na₂0 molar ratio of about 3.3. The initial aqueous sodium silicate solution was heated to 37°C and over a period of 30 minutes and with agitation, 2.449 liters of about 30 weight percent aqueous sulfuric acid and 137.426 liters of water were added as separate streams to the initial aqueous alkali metal silicate solution to neutralize about 80 percent of the N 2θ and to form a first reaction mixture. The first reaction mixture was heated with agitation to 95°C. During the heat-up 74.8 liters of water was added. The diluted first reaction mixture was then aged with agitation at 95^βC for 60 minutes. Over a period of 120 minutes, with agitation, and at a temperature of 95°C, a stream of 52.41 liters of additive aqueous sodium silicate solution containing about 13 weight percent Siθ2 and having an Siθ2 Na2θ molar ratio of about 3.3 and a stream of 9.449 liters of about 30 weight percent aqueous sulfuric acid were added to the aged diluted first reaction mixture to form a second reaction mixture. The pH of the second reaction mixture was 9.1. A stream of about 8 liters of about 30 weight percent aqueous sulfuric acid was added to the second reaction mixture with agitation at a temperature of 95°C to form a third reaction mixture having a pH of 4.5. The third reaction mixture was aged with agitation at 95°C for 30 minutes. With agitation, 6.57 liters of additive aqueous sodium silicate solution containing about 13 weight percent Si0₂ and having an Siθ2 Na2θ molar ratio of about 3.3 was added to the aged third reaction mixture at 95°C to form a fourth reaction mixture having a pH of 8.7. A fifth reaction mixture was formed by adding to the fourth reaction mixture with agitation and at a temperature of 95°C, 30.18 liters of additive aqueous sodium silicate solution containing about 13 weight percent Siθ2 and having an Si0₂:Na2θ molar ratio of about 3.3, and by adding 6 liters of about 30 weight percent aqueous sulfuric acid as necessary to maintain the pH at about 8.7. The sequential additions to form the fourth and fifth reaction mixtures were made over a collective time period of 84 minutes. The fifth reaction mixture was aged with agitation at 95°C for 45 minutes. With agitation, 3.5 liters of about.30 weight percent aqueous sulfuric acid was added to the aged fifth reaction mixture to form a sixth reaction mixture having a pH of 4.5. The sixth reaction mixture was aged with agitation for 60 minutes maintaining 95^βC and thereafter for about 900 minutes without temperature maintenance. The temperature at the conclusion of the 900 minute period was 66°C. The aged sixth reaction mixture was filtered in a filter press. The filter cake was washed with water until the conductivity of the filtrate had dropped to 90 micromhos/cm. The wet filter cake and added water were mixed with a Cowles blade to form a solid in liquid suspension containing 9.7 percent solids by weight. The suspension was dried in a Niro spray drier (inlet temperature about 360^βC; outlet temperature about 128^CC) to form the reinforced precipitated silica product. The product had a surface area of 232 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of 14 nanometers, and a total intruded volume of 3.09 cubic centimeters per gram.

EXAMPLE 3 An initial aqueous sodium silicate solution in the amount of 41314 liters was established in a reactor. The initial aqueous sodium silicate solution contained about 2 weight percent Siθ2 and had an Si0₂:Na₂0 molar ratio of about 3.2. The initial aqueous sodium silicate solution was heated to 34°C and over a period of 33 minutes and with agitation, 1086 liters of about 30 weight percent aqueous sulfuric acid and 11356 liters of water were added to the initial aqueous alkali metal silicate solution to neutralize about 80 percent of the Na2θ and to form a first reaction mixture. The first reaction mixture was heated with agitation to 95°C over a period of about 2 hours. The first reaction mixture was then aged with agitation at 95°C for 65 minutes. A total of 2557 liters of water were added during the heating and aging periods. Over a period of 119 minutes, with agitation, and at a temperature of 95°C, a stream of 6314 liters of additive aqueous sodium silicate solution containing about 12.6 weight percent Siθ2 and having an SiU2 Na2θ molar ratio of about 3.2, a stream of 1124 liters of about 30 weight percent aqueous sulfuric acid, and a stream of 549 liters of water were added simultaneously to the first reaction mixture to form a second reaction mixture. The pH of the second reaction mixture was 9.6. A stream of about 777 liters of about 30 weight percent aqueous sulfuric acid and a stream of 117 liters of water were added to the second reaction mixture with agitation at a temperature of 95°C'to form a third reaction mixture having a pH of 4.5. The third reaction mixture was aged with agitation at 95^βC for 30 minutes during which period 46 liters of water was added. With agitation, water and 890 liters of additive aqueous sodium silicate solution containing about 12.6 weight percent Siθ2 and having an Siθ2:Na2θ molar ratio of about 3.2 was added to the aged third reaction mixture at 95°C to form a fourth reaction mixture having a pH of 8.5. A fifth reaction mixture was formed by adding to the fourth reaction mixture with agitation and at a temperature of 95°C, water and 3528 liters of additive aqueous sodium silicate solution containing about 12.6 weight percent Siθ2 and having an SiU2: a2θ molar ratio of about 3.2 and by adding 846 liters of about 30 weight percent aqueous sulfuric acid as necessary to maintain the pH at about 8.5. The sequential additions to form the fourth and fifth reaction mixtures were made over a collective time period of 80 minutes. The fifth reaction mixture was aged with agitation at 95°C for 45 minutes. With agitation, water and 259 liters of about 30 5 weight percent aqueous sulfuric acid were added to the aged fifth reaction mixture to form a sixth reaction mixture having a pH of 4.5. A total of 568 liters of water was added during formation of the fourth through the sixth reaction mixtures. The sixth reaction mixture was aged with agitation and without temperature maintenance 10 for 653 minutes. The final temperature was 82^βC. The aged sixth reaction mixture was divided into two batches of about 40504 liters and 39747 liters, respectively. Each batch was filtered in a filter press. The filter cakes were washed with water until the conductivity of the filtrate had dropped to about 5 micromohs/cm. A 15 portion of the washed filter cakes from the first filter press batch was removed and set aside. The remainder of the washed filter cakes and added water were mixed with a Cowles blade to form a solid in liquid suspension containing 12 percent solids by weight. The suspension was dried in a Bowen spray drier (inlet temperature about 20 620°C; outlet temperature about 130°C) to form the reinforced precipitated silica product. The product had a surface area of 236 square meters per gram, a pore diameter at the maximum of the volume pore"size distribution function of 15 nanometers, and a total intruded volume of 3.2 cubic centimeters per gram. 25

GENERAL PROCEDURE FOR EXAMPLES 4-7 Unchillproofed lager beers were obtained from various breweries. These beers differed in brewing conditions resulting in a di ference in haze forming potential. Each beer was taken from 0 processing at the stage where it would normally be chillproofed according to the practice of that particular brewery.

The test materials were weighed in appropriate doses for addition to the beer. The weighed samples were placed in storage vessels and thoroughly flushed with carbon dioxide to eliminate all 5 air; then the beer was pumped in. After adding the beer, the system was mixed thoroughly by shaking, then allowed to stand for 90 minutes before filtration. A 3-liter sample of beer was used for each treatment, and a temperature of 1-2°C was maintained throughout the testing. Filtration included the use of diatomaceous earth filter aid with Celite® 512 diatomaceous earth as body feed (approximately 1.07 grams per liter) and also as a filter precoat (approximately 488 grams per square meter of filter area). The laboratory filter used in the tests had a diameter of 5.08 centimeters, and was sensitive to beer filtration characteristics that would be noted in a brewery. Carbon dioxide under pressure was used to push the beer through the filter. After filtration the beer was carbonated, bottled, and pasteurized before further evaluation.

Chillproofing effectiveness was determined by a haze-forcing test. This test was performed by storing samples of the bottled beer at 60^βC for five days, then chilling to l^βC and holding for two more days. The samples were then warmed to 10°C and haze measurements were made. Haze levels are expressed in formazin turbidity units (FTU). Higher numbers indicate higher levels of haze. The haze levels so obtained are reported in Tables 2-5 in the "5-Day" row. Haze measurements were also made on beer that had not been heat punished, and these haze levels are reported in Tables 2-5 in the "Initial" row. The differences between these two values are indices of the colloidal stability of beers and are reported in Tables 2-5 in the "Delta" row. As a rule, beers with a Delta FTU lower than 200 can be considered commercially acceptable.

Routine beer analytical properties were also determined for the heat punished samples and the results are shown in Tables 2-6. The analytical procedures employed are referenced in Table 1. Table 1

_PH pH is measured electrometrically.

Color Beer-10 Color from "Methods of Analysis of the American Society of Brewing Chemists". This is a Spectrographic Color Method (Standard Reference Method) and is determined by measuring absorbance at 430 nm.

Foam, sigma A. D. Rudin, Journal of the Institute of Brewing, Volume 63, Pages 506 et seq. (1957). This is a measure of foam collapse rate. Sigma values over 100 are acceptable.

Bitterness Units Beer-23 Beer Bitterness from "Methods of Analysis of the American Society of Brewing Chemists". This is the International Method.

Beer Protein, wt % T. S. Ma and G. Zuazaga, Industrial & Engineering Chemistry_t Analyst Edition, Volume 14 , Pages 280 et seq. (1942). This is a micro Kjeldahl technique.

Anthocyanogen, ppm Harris and Rickets, 1959 European Brewing Convention Proceedings_τ pages 299 et seq. (1959). This is a nylon powder technique.

The procedures cited in Table 1 are, in their entiretie incorporated herein by reference. EXAMPLE 4

Table 2 Chillproofing Normal Haze Potential Beer

EXAMPLE 5

Table 3 Chillproofing Normal Haze Potential Beer

Table 4 Chillproofing High Haze Potential Beer

EXAMPLE 6

Table 5 Chillproofing Normal Haze Potential Beer

The data of Examples 4-6 show that amorphous precipitated silica used in accordance with the principles of the present invention is an excellent chillproofing agent and is effective at dosages at least one-half that of a currently used commercial silica gel chillproofing agent. The data also show that none of the routine analytical properties were significantly changed by any of the chillproofing treatments using the amorphous precipitated silica. Further, the data show that the amorphous precipitated silica exhibits selectivity in respect of the proteins it adsorbs. EXAMPLE 7

Reinforced amorphous precipitated silica was produced according to the general procedure of Example 1 of United States Patent No. 4,495,167. This material had a surface area of 498 square meters per gram, a pore diameter at the estimated maximum of the volume pore size distribution function of less than 7 nanometers but an average pore diameter by nitrogen adsorption of 13 nanometers, and a total intruded volume of 2.85 cubic centimeters per gram.

Samples of two commercially available amorphous precipitated silicas were obtained and analyzed for physical properties. Hi-Sil® 132 amorphous precipitated silica was found to have a surface area of 193 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of 24 nanometers, and a total intruded volume of 2.36 cubic centimeters per gram. Flo-Gard® SP amorphous precipitated silica was found to have a surface area of 220 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of 26 nanometers, and a total intruded volume of 2.93 cubic centimeters per gram.

All three amorphous precipitated silicas and a commercially available silica gel chillproofer were tested for chillproofing effectiveness in accordance with the general procedure described above. The results are shown in Table 6.

Table 6 Chillproofing Normal Haze Potential Beer

Chillproofing Normal Haze Potential Beer

Product of Product of Commercial Flo-Gard® Example 1 of Example 1 of Silica Gel P US 4.495.167 US 4.495.167 ll r

The data of Example 7 show that amorphous precipitated silicas used in accordance with the principles of the present invention are excellent chillproofing agents. The data also show that none of the routine analytical properties were significantly changed by any of the chillproofing treatments using the amorphous precipitated silicas. Further, the data show that the amorphous precipitated silicas exhibit selectivity in respect of the proteins they adsorb.

Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except insofar as they are included in the accompanying claims.

Claims

CLAIMS :

1. In a process wherein a liquid medium in which protein is dissolved, suspended, or dispersed is contacted with amorphous precipitated silica and wherein at least a portion of said protein is adsorbed by said amorphous precipitated silica, the improvement wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 190 to about 600 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 7 to about 30 nanometers, and a total intruded volume of from about 2.3 to about 5 cubic centimeters per gram.

2. The process of claim 1 wherein after said liquid medium has been contacted with said amorphous precipitated silica, said amorphous precipitated silica is separated from most of the liquid of said liquid medium.

3. The process of claim 2 wherein said liquid medium is a beverage.

4. The process of claim 3 wherein said beverage is beer, winei distilled spirits, fruit juice, or vegetable juice.

5. The process of claim 2 wherein said amorphous precipitated silica is reinforced amorphous precipitated silica.

6. The process of claim 2 wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 9 to about 20 nanometers, and a total intruded volume of from about 2.6 to about 4.4 cubic centimeters per gram.

7. The process of claim 2 wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 13 to about 30 nanometers, and a total intruded volume of from about 2.6 to about 4.4 cubic centimeters per gram.

8. The process of claim 2 wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 13 to about 18 nanometers, and a total intruded volume of from about 3 to about 4.4 cubic centimeters per gram.

9. The process of claim 2 wherein at least about 90 percent by weight of said amorphous precipitated silica has gross particle sizes in the range of from about 1 to about 80 micrometers.

10. The process of claim 2 wherein said amorphous precipitated silica contains less than about 2 percent by weight alkali metal salt.

11. In a process wherein beer is chillproofed by contacting said beer with amorphous precipitated silica, the improvement wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 190 to about 600 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 7 to about 30 nanometers, and a total intruded volume of from about 2.3 to about 5 cubic centimeters per gram.

12. The process of claim 11 wherein after said beer has been contacted with said amorphous precipitated silica, said amorphous precipitated silica is separated from most of said beer.

13. The process of claim 12 wherein said amorphous precipitated silica is reinforced amorphous precipitated silica.

14. The process of claim 12 wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 9 to about 20 nanometers, and a total intruded volume of from about 2.6 to about 4.4 cubic centimeters per gram.

15. The process of claim 12 wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 13 to about 30 nanometers, and a total intruded volume of from about 2.6 to about 4.4 cubic centimeters per gram.

16. The process of claim 12 wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 220 to about 340 square meters per gram, a pore diameter at the maximum of the volume pore size distribution function of from about 13 to about 18 nanometers, and a total intruded volume of from about 3 to about 4.4 cubic centimeters per gram.

17. The process of claim 12 wherein at least about 90 percent by weight of said amorphous precipitated silica has gross particle sizes in the range of from about 1 to about 80 micrometers.

18. The process of claim 12 wherein said amorphous precipitated silica contains less than about 2 percent by weight alkali metal salt.

19. The process of claim 12 wherein the amount of said amorphous precipitated silica brought into contact with said beer is in the range of from about 50 to about 2000 parts of said amorphous precipitated silica per million parts of said beer, by weight.

20. The process of claim 12 wherein the temperature at which said amorphous precipitated silica and said beer are in mutual contact is in the range of from about -2°C to about +30°C.

21. The process of claim 12 wherein the contact time of said amorphous precipitated silica and said beer is in the range of from about 30 seconds to about 2 months.

22. In a process wherein a liquid medium in which protein is dissolved, suspended, or dispersed is contacted with amorphous precipitated silica and wherein at least a portion of said protein is adsorbed by said amorphous precipitated silica, the improvement wherein said amorphous precipitated silica has, on a coating-free and impregnant-free basis, a surface area of from about 190 to about 600 square meters per gram, an average pore diameter by nitrogen adsorption of from about 3 to about 19 nanometers, and a total intruded volume of from about 2.3 to about 5 cubic centimeters per gram.

23. The process of claim 22 wherein after said liquid medium has been contacted with said amorphous precipitated silica. said amorphous precipitated silica is separated from most of the liquid of said liquid medium.

24. The process of claim 23 wherein said liquid medium is a beverage.

25. The process of claim 24 wherein said beverage is beer, wine, distilled spirits, fruit juice, or vegetable juice.

26. The process of claim 24 wherein said beverage is beer.

27. The process of claim 26 wherein said average pore diameter by nitrogen adsorption is from about 6 to about 17 nanometers.

28. The process of claim 26 wherein said average pore diameter by nitrogen adsorption is from about 9 to about 14 nanometers.

29. The process of claim 26 wherein at least about 90 percent by weight of said amorphous precipitated silica has gross particle sizes in the range of from about 1 to about 80 micrometers.

30. The process of claim 26 wherein said amorphous precipitated silica contains less than about 2 percent by weight alkali metal salt.

31. The process of claim 26 wherein the amount of said amorphous precipitated silica brought into contact with said beer is in the range of from about 50 to about 2000 parts of said amorphous precipitated silica per million parts of said beer, by weight.

32. The process of claim 26 wherein the temperature at which said amorphous precipitated silica and said beer are in mutual contact is in the range of from about -2°C to about +30°C.

33. The process of claim 26 wherein the contact time of said amorphous precipitated silica and said beer is in the range of from about 30 seconds to about 2 months.