GB2074006A - Process for preparing microporous dry soluble coffee product - Google Patents

Abstract

A dry soluble coffee product in the form of particles or granules and having a microporous structure is prepared by spraying an aqueous extract or solution of autoclave coffee solids into an anhydrous organic solvent e.g. ethanol so as to dehydrate the extract and form microporous particles. The microporous particles are removed from the solvent and subsequently the product so prepared has a unique microporosity and is capable of sorbing, retaining and releasing volatile aromatic compounds.

Description

SPECIFICATION Process for preparing microporous dry soluble coffee product Technical field The present invention relates to soluble coffee.

More particularly, it relates to a process for preparing a dry soluble coffee product in the form of particles or granules which have a unique microporosity capable of sorbing and retaining volatile aromatic compounds and releasing these volatile aromatic compounds in a controlled manner.

Background art Many commercial soluble coffee products are enhanced with volatile aromatic compounds by combining the soluble coffee product with pure coffee oil or aroma-enriched coffee oil so as to provide the soluble coffee product with an aromatic quality more like that of roasted and ground coffee.

However, aromatizing a soluble coffee product with coffee oil presents plant processing problems in recovery of the oil from the roasted coffee beans in handling the resulting presscake, and in storage of the oil.

Generally, headspace aromatization of soluble coffee products without the use of coffee oil as an aroma source or aroma carrier has not met with marked commercial success. It is known that conventionally produced soluble coffee solids lack the capacity or property of sorbing, retaining and releasing volatile aromatic compounds such as are contained in, or added to, coffee oil.

The prior art also discloses porous soluble coffee particles having the capacity to sorb large quantities of volatile aromatics, to retain the aromatics for extended periods of time, and subsequently, to release the aromatics under repeated in-use conditions such as may be encountered in opening and closing a container in which the particles are packaged are described and claimed. The aromatized soluble coffee particles may be added in small amounts and uniformly admixed with unaromatized soluble coffee solids to provide a soluble coffee product with a desirable coffee aroma such as the aroma of freshly roasted and ground coffee.

The porous soluble coffee particles are characterized by having an average diameter of less than 200 microns and a microporous structure wherein the most probable radius of the pores is 150 A or less and the pore volume per gram of dry soluble coffee solids is from 3 to 30 microliters per gram. These microporous structured soluble coffee particles are prepared by instantaneously freezing an aqueous extract or solution of coffee solids as by spraying the extract solution into a cryogenic fluid and subsequently freeze-drying the frozen particles, spheres or granules.

While the methods described and claimed in the hereinbefore mentioned patent applications are capable of producing microporous structured soluble coffee, there would be advantages to a method or process whereby microporosity, pore volume and surface area might be increased.

Disclosure ofthe invention It has now been discovered that a microporous dry soluble coffee product may be obtained by (a) spraying an aqueous extract or solution of autoclave coffee solids into an an hydros organic solvent so as to dehydrate the extract and form microporous particles or granules of soluble coffee solids; (b) recovering the dehydrated extract in the form of microporous particles from the solvent; and (c) removing residual solvent, under vacuum, from microporous particles.

The resulting dry soluble coffee paticles are found to have a microporous structure which makes them suitable for sorbing, retaining and releasing aromatic volatile compounds.

Soluble coffee particles prepared by the process are found to possess a micropore volume (radii of 6150 ) of from about 5 to 560 microliters per gram and a surface area of from about 7 to 210 m2/g.

The invention offers an improved method for the preparation of discrete microporous structured particles in that expensive and costly freeze-drying equipment is not required.

By spraying an extract or solution of autoclave coffee solids into an anhydrous organic solvent, a specific microporous structure of extremely high surface area may be formed which structure may also be further controlled by modifications of spraying pressures, extract makeup, extract concentration, solventtype and solvent temperature and the like.

The resulting microporous dry product exhibits the ability to "fix" various aromas.

Best mode for carrying out the invention The starting extract may be a water solution of autoclave coffee solids at 10 to 60% soluble solids, formed by any one or a combination of various techniques including percolationlextraction of roasted and ground coffees, followed by autoclave steaming of the columns, usually at 180"C, dissolving previously dried soluble autoclave coffee solids in water, and the like. Evaporation may be used to achieve desired concentration with any of the foregoing. Generally, the extract temperature is maintained between about 32 to 30"C.

Any anhydrous organic solvent such as ethanol, methanol, isopropyl alcohol acetone and the like may be employed provided it serves as a dehydrating medium and it is a solvent in which coffee is relatively insoluble. Preferably, ethanol is employed.

Aqueous solutions of soluble autoclave coffee solids (25 to 35%) are sprayed into a vessel containing pure alcohol (ethanol or methanol) preferably using high pressure nozzles (600 to 1100 psig). The alcohol is maintained at ambient temperature but preferably it is cooled with addition of liquid nitrogen to drop its temperature down to about -1 00 C. The ratio of aqueous extract to alcohol is kept around or below 1:20 to obtain a fairly dry solid.

At the end of the spraying period, usually a few minutes, the alcoholic suspension is allowed to settle for about one hour (and to bring the tempera ture to above 0 C if it was lowered before spraying).

This is followed buy a quick filtering of the dehydrated solid and finally an overnight vacuum solvent drying in a vacuum oven. The temperature of the oven is kept between ambient temperature and 90"C.

The microporosity of the soluble coffee product is characterized by determining the nitrogen adsorption isotherm at liquid nitrogen temperature. From the isotherm the following parameters are calculated: i) Surface area (m2lg); ii) pore volume (lli/9); iii) pore volume distribution (AVIAr, in IlA); and iv) pore surface area distributions (m2lg for a given pore range).

All the above parameters are printed out by a Micromeritic 2500 Digisorb, available from Micromeritics Instrument Corporation. However, the pore volume distribution may be recalculated to be AV/Ar rather than AV as given by the Digisorb.

Details of the pore size analysis are given in hereinbefore referred to Application Serial No.

086,367. The pore surface area distribution (ASp) is related to pore volume distribution (AVp of that particular group of pores) by the following equation Sp = 2 asp rc where rc is the average pore radius of that group of pores.

Upon analysis the microporous structured pro ducts are found to have pore volumes of from about 5 to 560 microliters per gram and micropores whose radius is 150 r4 and surface areas of from about 7 to 210 m2/g.

The volatile aromatic compounds associated with coffee, whether natural or synthetic, to be sorbed on the microporous structured product may be derived from many sources well-known to those skilled in the art. Depending on the method of contact to be employed, the compounds may be present as a component of a gas, a liquid condensate or a condensed frost.

The method of contacting the microporous parti cles with the volatile aromatic compounds for the purpose of sorbing aroma within the particles can also be many and varied. The use of high pressure and/or low particle temperatures may be employed in order to maximize the quantity of aroma sorbed or to shorten the period of time required to achieve a desired level of aromatization.

The microporous structured soluble coffee pro duct prepared by the process of the invention has the capability of sorbing as much as 2% by weight of volatile aromatic compounds. This is, in general, in excess of that which is required and, depending on how the aromatized soluble coffee solids are utilized, the aromatized particles will contain volatile aroma tic compounds at a level of from 0.05 to 20 milli grams per gram of solids, 0.2 to 0.5% by weight.

Example I One hundred miililiters of a coffee extract containing 33% by weight soluble autoclave coffee solids is sprayed by means of a glass chromatographic nozzle into a largevessel containing 3.8 liters of pure ethanol. The ethanol was at room temperature and was stirred during the spraying operation. Thereafter particles of soluble coffee were filtered from the ethanol and these particles were put in a vacuum oven (25 inches Hg. vacuum and about 90"C) overnight to remove residual ethanol. The resulting particles were found to have a microporous structure, a pore volume of 66.2 microliters per gram (ras150 Â) and a surface area of 42.2 m2/g.The particles were kept out of contact with moisture and contacted with grinder gas frost at a level by weight of 2 parts frost to 1 part of particles in a Parr bomb heated to about 20"C. The resulting aromatized particles were combined and packaged with unplated and un-aromatized spray dried coffee agglomerate at a level of about 0.5% by weight. The jar aroma possessed by this sample after one week storage at room temperature was found to be comparable to week-old, grinder gas-enriched, oilplated agglomerate.

Example 2 In this Example only high purity autoclave coffee solids are used. This material is practically insoluble in pure ethanol. The process is thus essentially a dehydration process with no or very little etching (since caffeine and chlorogenic acid are relatively soluble in ethanol).

Using a high pressure (600 to 1100 psig) a 33% coffee autoclave solids solution is sprayed into ethanol at ambient temperature. Microporous particles having a surface area of 40 m2/g are produced.

Significantly higher surface areas (over 200 m2ig) are obtained by spraying these autoclave coffee solids into cold ethanol (about 8000).

The dry particles were found to have a microporous structure pore volume ranging from 5 to 560 microliters per gram (r < 150 A) and a surface area ranging from 7 to 210 m2/g.

The solvent-free dry particles were subsequently chilled in dry ice under a dry atmosphere and mixed with coffee grinder gas frost. The chilled particles, were then packaged in glass jars with unplated, agglomerated spray-dried coffee solids at the level of 0.75% by weight of spray-dried solids. Upon storage initial opening and during a standard sevenday, in-use cycle, a pleasing headspace aroma was noted.

Industrial applicability The microporous structured soluble coffee product prepared by the process of this invention is utilized as a sorbent for volatile aromatic compounds. The process offers an improved method for the preparation of discrete particles of the microporous structured soluble coffee products.

Claims (8)

1. A process for preparing a microporous dry soluble coffee product comprising: (a) spraying an aqueous extract or solution of autoclave coffee solids into an anhydrous organic solvent so as to dehydrate the extract and form microporous particles or granules of soluble coffee solids; (b) recovering the dehydrated extract in the form of microporous particles from the solvent; and (c) removing residual solvent, under vacuum, from the microporous particles.

2. A process as in Claim 1 in which the microporous particles have a micropore volume (radii of s;1 50 ) of from about 5 to 560 microliters per gram, a surface area of from about 7 to 210 m2/g.

3. A process as in either of Claims 1 and 2 in which the anhydrous orgaic solvent is ethanol.

4. A process as in Claim 3 in which the ethanol is maintained at a temperature of +25"C to -100"C.

5. A process as in either of Claims 3 and 4 in which ratio of aqueous extract to ethanol is 1:20.

6. A process as in any one of Claims 1 to 5 in which the aqueous extract of autoclave coffee solids has a soluble solids content of 25 to 35% and spraying is carried out at a pressure of 600 to 1100 psig.

7. A process as claimed in Claim 1 for preparing a dry soluble coffee product substantially as hereinbefore described.

8. A dry soluble coffee product when prepared by a process as claimed in any one of Claims 1 to 7.