CA2171650A1 - Method of producing a malt beverage having improved flavor and improved flavor stability - Google Patents

Abstract

A method of producing a non-alcoholic malt beverage having improved flavor and long-term flavor stability. A non-alcoholic malt beverage is contacted with yeast, either in a batch process in which the yeast is admixed with the non-alcoholic malt beverage, or by passing the non-alcoholic malt beverage through a column of immobilized yeast, to reduce the stale flavor carbon-yls to flavor inactive alcohols. The yeast is then removed from the non-alcoholic malt beverage and the beverage is then processed and packaged using conven-tional techniques.

Description

~ 2t71~50 -METHOD OF PRODUCING A MALT BEVERAGE HAVING

Background of the Invention All malt beverages are subject to flavor changes over a period of time. Some of the flavor changes are advantageous. For example, the reduction during the first week after packaging of certain sulfur flavors associated with a freshly fermented malt beverage is generally considered to improve flavor. However, the development over time of objectionable flavors, such as "papery", "stale", "cardboard" or "oxidized" flavors is an oxidation problem associated with all categories of malt-based beverages, especially low alcohol and non-alcoholic beers. `~
It is widely believed that carbonyl compounds, i.e. vinyl ketones and aldehydes, cause the objectionable flavors in malt beverages. In particular, volatile, unsaturated aldehydes are associated with undesirable flavors in beer, with the severity of these off-flavors increasing with increasing carbon chain length. Similar-ly, vinyl ketones can lend a stale metallic flavor to beer. While virtually all carbonyls are present in beer at concentrations below their flavor threshold, their ability to synergistically contribute to oxidized beer flavor has led to the conclusion that the oxidized beer flavor is the net result of a complex mixture of many volatile carbonyls.
There are a number of different mechanisms involved in the production of off-flavor carbonyls in malt beverages or beer. Oxidation reactions are cumulat-ive throughout the brewing process and in some cases begin even before raw materials reach the brewery. As an example, during malting, the sequential action of barley lipase, lipoxygenase, and hydroperoxide isomerase enzymes produce hydroperoxides and ketols, which, in a series of non-enzymatic steps, degrade into stale flavor aldehydes.
While some aldehydes formed prior to the brewhouse will `~ 2171650 _, be driven off during the kettle boil, many of the inter-mediates of the degradation process are carried through into the wort and ultimately into the beer.
A second type of malt derived precursor potentially involved in the development of stale flavor carbonyls is malt amino acids. During malt kilning and wort boiling, non-enzymatic browning reactions between sugars and amino acids, besides producing browning pigments, also ultimately lead to the production of carbonyls.
In addition to malt, a second raw material used in brewing, i.e. hops, has also been implicated in pro-viding precursors for oxidized beer flavor. During the kettle boil, hop alpha acids are isomerized into iso-alpha acids. It has been shown that isohumulones candegrade through oxidation into alkenals and alkadienals in the presence of melanoidins and higher alcohols.
Aldehydes which are formed in this manner begin to appear during the kettle boil and continue evolving throughout the brewing process.
In addition, yeast produced metabolites, i.e.
higher alcohols, have also been implicated as precursors for stale flavor carbonyls. Formed during the fermenta-tion stage of brewing, it is believed that iron and copper catalyzed oxidation of higher alcohols directly leads to the production of the corresponding aldehydes.
Lastly, it has also been suggested that long chain aldehydes can be produced in beer via aldol condensation of shorter chain aldehydes regardless if they are formed via oxidation or higher alcohols.
Therefore, it is apparent that the stale flavor carbonyls can arise in the malt beverage from a combina-tion of various precursors, such as malt fatty acids, hop iso-alpha acids, malt amino acids, and yeast produced higher alcohols through a variety of different oxidative mechanisms. In some cases these oxidation reactions begin with the raw materials even before they reach the -brewhouse, while others either occur first in the brew-house, continue in the brewhouse, or are initiated during fermentation.
The development of carbonyls is impacted by the redox state of wort and beer. There are at least four groups of substances which possess the ability to lower the redox potential, hydroxyflavin polyphenols, melanoidins, reductones, and yeast. The first three of these substances originate directly or indirectly from the raw materials used to produce beer. Each can exist in a reduced or oxidized state, possessing only finite abilities to resist redox changes. Hence, excessive oxygen uptake through abnormally high agitation or turbulence during mashing, kettle boiling or hot wort transfer can oxidize greater quantities of melanoidins, hydroxyflavin polyphenols, and reductones, ultimately resulting in poor resistance to the development of stale flavor carbonyls in the packaged product. Similarly, as air and dissolved oxygen levels increase in packaged beer, so does the rate and degree of development of the stale flavor carbonyls. For this reason, brewers have long focused on minimizing the introduction of oxygen into beer at any point during fermentation, aging, finishing, packaging and retail storage.
Equally important to oxygen control is the need to minimize the levels of transition metal ions in brew-ing, which play a role in activating oxygen into free radicals, particularly copper and iron ions. Cuprous ions catalyze the formation of oxygen free radicals from molecular oxygen in reactions, which are coupled with various reducing agents. These free radicals can then participate in the oxidation of unsaturated hydroxy fatty acids to produce stale flavor carbonyls.
Yeast also plays a critical role in maintaining a low redox state in the beer and control of the forma-tion of stale flavor carbonyls. Yeast is an efficient scavenger of dissolved oxygen in beer and wort. In spite -of the evidence concerning the harmful effects of oxygen and oxygen free radicals on the formation of stale flavor carbonyls, oxygen must be present in the wort at the start of fermentation, as it is an essential nutrient for yeast growth. Oxygen, as well as pre-formed, unsatur-ated, fatty acids and sterols in the wort, are normally the first nutrients to limit yeast growth during fermen-tation. As soon as these materials are exhausted the rate of attenuation slows dramatically. Yeast will effectively continue to scavenge any dissolved oxygen entering into the beer from whatever source. Once the yeast is removed from the beer after fermentation, this natural resistance to oxidation is lost and the product becomes sensitive to oxidation.
A second role yeast plays in maintaining a low redox state in beer is through its production of endogen-ous sulfur dioxide. Yeast forms sulfur dioxide as a by-product of the biosynthetic pathways leading to the production of sulfur containing amino acids. Once in the beer, sulfur dioxide is an efficient scavenger of oxygen free radicals, thereby inhibiting the free radical reactions in beer which produce the stale flavor aldehydes.
The third role yeast plays in regard to staling aldehydes relates to the strong reducing ability of yeast. The ability of yeast to regenerate oxidized nicotinamide adenine dinucleotide (NAD+) from reduced NADH is crucial for its ability to provide oxidized NAD+
as an essential co-factor in glycolysis (where it participates in the oxidation of glyceraldehyde-3-phosphate). This is primarily accomplished via the reduction of acetaldehyde into ethanol by alcohol dehydrogenase, where NADH acts as the co-factor providing the source of hydrogen atoms - regenerating oxidized NAD+
in the process. There are, however, other metabolic means by which yeast can regenerate oxidized NAD+, such as the consumption of reduced NADH in biosynthetic path--ways leading to the production of cell lipids, amino acids and nucleic acids, as well in the direct reduction of aldehyde and ketone carbonyls into alcohol (e.g., VDK
into acetoin and 2,3 butanediol, aldehydes into higher alcohols, dihydroxyacetone into glycerol, 2,3-pentanedi-one into 2,3-pentanediol).
Attempts have been made in the past to protect alcoholic and non-alcoholic malt beverages from the development of oxidized flavors by adding sulfur dioxide in the form of bisulfite, to thereby slow the development of stale flavors, as described in U.S. Patents 1,217,641, 1,234,255 and 2,892,718. Improvements to the use of sulfur dioxide alone are taught in U.S. Patents 2,658,829, 2,892,718, 3,095,3S8 and 3,770,454, which describe a combination of ascorbate salts and a source of bisulfite.
A more direct approach to the removal of stale flavor aldehydes from the brewing process has also been described in U.S. Patent 4,100,180, where solvent extrac-tion of long chain unsaturated aldehyde precursors produced via enzymatic oxidation of long chain fatty acids from malt is achieved.
The literature also suggests the scavenging of dissolved oxygen from packaged beer to prevent the forma-tion of stale flavor aldehydes. U.S. patents 5,105,633 and 5,298,264 describe the immobilization of yeast in food grade wax or paraffin to coat either the inside surface of the container, or the surface of the closure of the container, so that the yeast will remove any headspace oxygen from the packaged beer, thus achieving flavor stability.
It has also been proposed in the past to utilize immobilized yeast in the primary fermentation process. More particularly, U.S. Patents 4,350,765, 4,680,263, 4,698,224, and 4,659,662 show various types of inert particulate material being used as the support or carrier for the immobilized yeast.

-The use of immobilized yeast has also been suggested in the secondary fermentation or maturation of beer. As described in U.S. Patent 4,915,959, a column of immobilized yeast is used in a continuous secondary fermentation of beer to reduce the concentration of diacetyl to acceptable levels.
Summary of the Invention The invention is directed to a method of producing a malt beverage having improved flavor, as well as improved long term flavor stability.
In a preferred form of the invention, a fully fermented alcoholic beer is initially produced by conven-tional techniques. The beer is then filtered to remove yeast and dealcoholized by conventional processes, such as centrifugal evaporation, reverse osmosis, membrane dialysis, vacuum evaporation, or the like, to produce a non-alcoholic beer typically having less than 0.5% by volume of alcohol.
Normally a dealcoholized beer is then finished and packaged without any additional contact with yeast.
However, in accordance with the invention, the de-alcoholized beer is contacted with yeast, either in the form of a high solids yeast cake containing at least 20%
yeast solids by weight to produce a cell count of at least 50,000,000 yeast cells per ml of dealcoholized beer, or alternately, passing the dealcoholized beer through an immobilized yeast column containing 1o8 to 109 cells per ml of carrier. During the contact period, the dealcoholized beer is maintained at a temperature of about 33F to 65F, for a period of about 0.5 to 24 hours. During this contact period, the yeast acts to reduce the stale flavor carbonyls to flavor inactive alcohols, thus improving the flavor of the beer, as well as improving the long-term flavor stability.
The invention differs from traditional techniques, in that the yeast is not utilized for fermentation or maturation (i.e. diacetyl reduction).

2~71650 -Instead the yeast is added to an already produced non-alcoholic beer which does not undergo further fermentation, but only uses the reducing power of yeast to reduce stale carbonyls into flavor inactive alcohols.
DescriPtion of the Preferred Embodiment There are certain terms that are recognized in the brewing industry, and are used in the description and claims of the present application. For example, "alcoholic beer", means a malt-based beverage with an alcohol content in the range of 3.0% to 5.5% (v/v), a "high alcohol beer", means a malt-based beverage with an alcohol content of over 5.5% (v/v), a "low alcohol beer", means a malt-based beverage with an alcohol content of 0.5% to 3.0% (v/v), and a "non-alcoholic beer", means a malt-based beverage with an alcohol content of less than 0.5% (v/v).
In a preferred form of the invention, a non-alcoholic malt beverage or beer is produced by dealcohol-izing an alcoholic beer which has undergone complete fermentation, as well as chill-proofing and processing to remove the yeast. The dealcoholization can be achieved by conventional techniques, such as using an Alfa-Laval Centritherm, which is a low temperature centrifugal vacuum distillation, in which the beer is spread as a thin layer, less than 0.1 mm thick, and indirectly steam heated to 100F, and separated under -0.95 bars pressure to produce a dealcoholized concentrate and a condensate -containing approximately 97% of the original ethanol, as well as other beer volatiles.
Other conventional methods of dealcoholizing a malt beverage can be utilized, such as reverse osmosis, membrane dialysis, or vacuum evaporation.
Normally, the dealcoholized concentrate is then finished by adjusting with carbonated dilution water, possibly adding a carbohydrate priming solution, and/or a post-fermentation hop addition, and then packaging.

217i6~0 However, in the invention, the dealcoholized concentrate, before any of these adjustments, is contact-ed with a high concentration of yeast to effect a reduction of the stale flavor carbonyls to thereby improve the flavor characteristics of the beer and improve the long term flavor stability.
The yeast to be used in the process of the invention can be an ale or lager culture normally employed in the brewing industry, or any commercially available isolate of yeast belonging to the genus Saccharomyces, including species of S. cerevisiae employed in the baking industry.
The dealcoholized beer is contacted with the yeast either through a batch process, or by passing the beer through a column of immobilized yeast. In the case of a batch process, a high solids yeast cake containing at least 20% yeast solids by weight is added to the beer to provide a concentration of 50,000,000 to 400,000,000 cells per ml. The mixture is maintained at a temperature in the range of 33F (0.6C) to 65F (18.3C) for a period of about 0.5 to 24 hours, with slow agitation.
During this period, the yeast will effect the reduction of the stale flavor carbonyls to flavor inactive alcohols.
With the use of an immobilized yeast column, the supporting medium or carrier can be particles of an inert material such as glass beads, fossil infusoria, polysaccharide gels, semi-permeable alginate gels, photo-crosslinkable resins, or the like. A static or fluidized bed can be employed. In a preferred form of the invention, the immobilized support consists of sintered glass beads having a double-pore structure, including both micro and macro pores, which permits high density yeast colonization by adsorption within the pores as well as on the bead surfaces. The immobilized yeast will typically have a concentration of between 108 to 109 cells per ml of carrier. The beer is normally flowed 2~71~50 -g through the immobilized yeast column at a rate of about 0.5 to 4 bed volumes per hour and the beer has a temperature in the range of 33F (0.6C) to 65F
(18.3C). Again, the contact between the non-alcoholic beer and the immobilized yeast will reduce the stale flavor carbonyls in the beer to flavor inactive alcohols, thereby improving the flavor characteristics of the beer.
No fermentation will occur during the contact of the beer with yeast, due to the fact that the dealcoh-olized product is prepared from fully fermented alcoholicbeer, and the dealcoholized beer contains no significant amounts of residual fermentable carbohydrates. In addi-tion, as the VDK (vicinyl diketone) levels are already below commonly acceptable flavor threshold values (50 ppb), any reduction of VDK during this process is incidental to the overall objective of reducing stale favor carbonyls.
After the contact with yeast has been completed, the yeast is separated from the beer by any commonly used separation technique. When batch condi-tions are employed, it may be necessary to first remove yeast by centrifugation prior to pre-filtration, whereas when an immobilized yeast column is utilized, only a pre-filtration may be required.
After the yeast has been separated, the non-alcoholic concentrate is finished in a manner typically practiced in the brewing art, including the addition of add-back beer, dilution water, carbohydrate priming, and post-fermentation hop additions, to produce a finished non-alcoholic beverage containing less than 0.5% alcohol (v/v) .
The ability of yeast to reduce aldehydes into flavor inactive alcohols through yeast reducing power is shown in the following Table:

-TABLE I

Aldehyde or Alcohol Concentration (ppm) Zero TimeControlYeast Treated Aldehyde SampleSample Sample Propanol 79.2 79.3 2.7 Butanol 78.2 84.3 3.6 Pentanal 78.1 85.4 5.9 ~x~n;:~1 75.9 78.6 7.2 Octanal 78.4 70.0 4.5 Nonanal 74.0 63.5 21.7 Total Aldehydes 463.8 461.1 45.7 Alcohols 2 5 Propanol 0.7 2.5 47.5 Butanol 1.3 0.8 46.3 Pentanal 5.2 5.6 6.2 Hexanol 0.4 1.2 42.1 Octanol 0.3 0.8 30.4 3 5 Total Alcohols 8.0 10.9 172.4 In the above Table I, the Zero Time Sample was the original aqueous matrix containing the listed aldehy-des and alcohols. The concentration of aldehydes in the aqueous matrix was considerably higher than the aldehyde concentration found in a normal beer. A portion of the Zero Time Sample was used as the control sample and main-tained at a temperature of 56F (13.3C) for one hour without any yeast addition. The second portion of the Zero Time Sample was treated with brewer's yeast to provide a yeast concentration of 200,000,000 cells/ml and held at a temperature of 56F (13.3C) for a period of one hour.
The test results shown in the above Table I
shows that the aldehyde content was reduced from 461.1 ppm to 45. 7 ppm by the yeast treatment, while the concentration of higher alcohols increased from 10.9 ppm to 172. 4 ppm. These test data show the strong reducing " 2171~;50 power capability of yeast to reduce off-flavor aldehydes to flavor inactive alcohols.
The following examples illustrate the method of the invention:
EXAMPLE I
A 9.4 liter glass column was filled with 5.0 liters of washed SIRAN porous glass beads and sterilized with steam for 30 minutes at 250F (121C). After cool-ing, the bioreactor column was inoculated with a mixture of a yeast suspension of the genus Saccharomyces and wort, and maintained for 12 hours at 56F (13.3C).
Fresh unhopped wort was then pumped through the column in a closed loop system at 56F (13.3C) for a period of 7 days to promote yeast growth and increase selection pressure in favor of yeast cells with better adherence properties. A non-alcoholic beer concentrate was then fed through the immobilized yeast column at a flow rate of 3.0 bed volumes per hour, and at a temperature of 56F
(13.3C). The first 3.0 bed volumes were not collected in order to rinse out any residual beer solids remaining in the column after the colonization phase. Non-alcoholic beer concentrate eluting through the column over the next 12 hour period was then recovered and processed in the traditional manner. A control non-alcoholic malt beverage was prepared from the same batchof concentrate used to produce the test beverage, except that it was not passed through the immobilized yeast column before processing and finishing in the traditional manner. Both the yeast treated beverage and the control beverage were tested for flavor evaluation by a trained flavor test panel.
The flavor test results of the beer produced in Example I are shown in the following Table:

21 71 ~50 -TABLE II
Preference Preference Beverage No. of Correct For Control For Yeast Age Tasters Identification Beverage Treated Beverage Fresh 32 21 11 21 Abused32 21 9 23 30 Days 28 19 10 18 60 Days 28 20 14 14 Totals120 81 44 76 In the above Table II, the "abused" sample was stored for four days at 100F (37.8C), while the "30 days" and "60 days" samples were stored at room tempera-ture for 30 days and 60 days, respectively.
In the duo-trio difference test, the tester was required to correctly identify which sample was different from the reference sample.
As shown in Table II, in the duo-trio differ-ence test evaluations, the panel reported a significant difference and preference for the immobilized yeast treated beverage (at the 908 confidence level or greater).
The analytical parameters of the control and yeast treated non-alcoholic malt beverages from Example I
are shown in the following Table:

21 71 b50 TABLE III
Attribute ControlYeast Treated Original Gravity, % w/w 5.25 5.19 Real Extract, % w/w 4.66 4.62 Alcohol, % v/v 0.29 0.28 Alcohol, % w/w 0.37 0.37 Color 2.3 2.3 pH 4.05 4.07 Bitterness United, mg/L 11.3 11.2 Ethyl Acetate, mg/L 1.13 0.70 Isoamyl amyl acetate, mg/L 0.10 0.09 Ethyl hexanoate (ppm) 0.01 0.01 Ethyl octanoate (ppm) 0.03 0.02 Total Esters (ppm) 1.26 0.82 Propanol (ppm) 0.43 0.35 Isobutanol (ppm) 0.99 0.54 n-Butanol (ppm) 0.24 0.31 Isoamyl Alcohol (ppm) 6.85 3.51 Phenylethyl Alcohol (ppm) 7.50 5.30 Total Alcohols (ppm) 16.01 10.01 From the above data in Table III it can be seen that the control and yeast treated malt beverage had similar attributes although the yeast treated beverage actually had lower levels of both ester and higher alcohols than the control beverage while the alcohol (ethanol) content remained virtually unchanged, showing that the improved flavor was not the result of any active yeast fermentation.
EXAMPLE II
In a 10 gallon fermenting vessel, 37 liters of dealcoholized beer concentrate, which had been dealcohol-ized using an Alfa-Laval Centritherm, was combined with centrifuged brewer's yeast containing 25~ yeast solids to achieve a density of 400,000,000 yeast cells per ml. The mixture was stirred for 4 hours at 56F (13.3C), and the yeast was subsequently removed by centrifugation.
Following yeast removal the non-alcoholic concentrate was 2171~50 ~ -14-pre-filtered and finished in a conventional manner by the addition of dilution water, carbohydrate priming and a post fermentation hop addition.
A control non-alcoholic malt beverage was prepared from the same concentrate used in the yeast treated beverage and was finished in the identical manner. Both the yeast treated malt beverage and the control were tested for flavor evaluation by a trained flavor test panel.
The following Table shows the results of the flavor panel test:
TABLE IV

ATTRIBUTE Y C Y CY C Y C Y C Y C
FRUITY 2.01.8 1.81.6 2.31.92.42.12.62.42.22.0 HOPPY 3.23.0 3.43.2 3.63.53.63.13.23.03.53.2 BITTER 3.23.8 3.63.8 3.12.93.13.12.62.63.13.2 SWEET 2.42.2 2.42.6 2.01.92.52.62.02.02.32.3 BODY 3.83.8 4.04.0 2.92.63.03.02.02.03.13.0 AFTERBITTER 0.41.0 1.40.6 1.41.41.31.81.00.81.11.2 ASTRINGENT 0.80.8 0.81.0 2.11.91.81.31.00.81.41.2 OXIDIZED 0.60.8 0.80.2 0.81.90.51.50.22.00.61.4 GRAINY 0.60.8 2.22.4 2.43.32.53.42.83.02.22.9 SULFITIC 0.02.2 0.00.0 0.00.00.00.00.80.60.10.1 MUSTY 0.60.0 0.00.0 0.00.00.00.00.00.00.00.0 BURNT 0.00.0 0.00.0 0.00.00.00.10.00.00.00.0 MEDICINAL 0.00.4 0.00.0 0.00.00.00.00.00.00.00.1 OVERALL 4.43.0 4.03.6 4.63.34.63.65.03.64.53.4 In the above Table "Y" represents the yeast treated sample, while "C" represents the control. The "abused" sample was stored for four days at 100F
(37.8C), while the "1 month", "2 month", "3 month"
samples were stored at room temperature for one month, 2 1 7 1 hSO

two months, and three months, respectively. Each proper-ty of the two beverages was rated on a scale of 0 to 8.
The results of the flavor panel tests, as shown in Table IV were quite dramatic and showed a statistical-ly significant preference for the yeast treated beverage.
In terms of specific attributes, the yeast treated bever-age was rated as being significantly less grainy and oxidized, but significantly more fruity and hoppy.
A duo-trio flavor evaluation of the non-alcoholic beverages prepared in accordance with ExampleII, also demonstrated a significant difference between the control beverage and the yeast treated beverage, with 16 of 20 tasters correctly identifying which sample was different from the reference sample and an over-whelming preference, 17 to 3, for the yeast treated non-alcoholic beverage. This preference carried through to a tasting of three months old product where once again a significant difference was detected between the test and control beverages (with 16 of 20 tasters again correctly identifying which sample was different from the reference sample), with an even more overwhelming preference (19 to 1) for the yeast treated non-alcoholic beverage.
The analytical parameters of the control beverage and yeast treated beverage prepared in accord-ance with Example II and after finishing are shown in thefollowing table:

TABLE V
Yeast Treated Control Attribute BeverageBeverage Original Gravity (% w/w) 3.85 4.23 Real extract (% w/w) 3.23 3.61 Alcohol (% w/w) 0.31 0.31 Alcohol (% w/w) 0.31 0.31 Alcohol (% v/v) 0.40 0.40 10 Color (SRM) 1.7 2.0 BU (ppm) 8.9 10.4 VDK (ppm) 0.02 0.03 Calories 55 58 Foam Stand (Minutes) 1.78 2.54 15 Foam Cling (Minutes) 3.9 4.0 Original Haze (FTU) 67 43 Fructose (% w/w) 0.14 0.31 Glucose (% w/w) 0.16 0.25 Maltose % (w/w) 0.09 0.14 20 Acetaldehyde (ppm) <1.5 <1.5 Ethylacetate (ppm) 1.16 1.42 Isoamyl acetate (ppm) <1.5 >1.5 Ethyl octanoate (ppm) 1.54 1.57 Phenylethyl acetate (ppm) <1.5 <1.5 Total Esters (ppm) 2.70 2.98 1-propanol (ppm) 0.31 0.71 Isobutanol (pp) 1.48 1.34 1-butanol (ppm) <1.5 >1.5 Isoamyl alcohol (ppm) 7.01 6.83 Phenylethyl alcohol (ppm) 12.19 15.08 Total Alcohols (ppm) 20.98 24.01 It is evident from the above Table V that the improved flavor ratings in the yeast treated beverage is not the result of formation of additional aroma volatil-es, as both ester and higher alcohol contents were slightly lower in the yeast treated beverage, as compared to the control. Further, the alcohol (ethanol) contents of the two beers were identical, again indicating that the improved flavor was not achieved through active yeast fermentation.
While the above description shows the use of the invention as applied to a non-alcoholic malt bever-age, it is contemplated that improved flavor and flavorstability can also be achieved through use of the method of the invention with alcoholic beers (especially those destined for export markets). As the alcoholic beer is fully fermented and contains no residual fermentable carbohydrates, the contact with yeast will not produce further fermentation, but instead the yeast will act to reduce the stale flavor carbonyls to flavor inactive alcohols, to thereby improve the flavor and flavor stability of the alcoholic beer.

Claims (9)

1. A method of producing a non-alcoholic malt beverage having improved flavor characteristics and long-term flavor stability, comprising the steps of preparing a fully fermented alcoholic malt beverage, removing alcohol from the malt beverage to provide an alcohol content less than 0.5% by volume and thereby produce a non-alcoholic malt beverage, contacting the non-alcoholic malt beverage with yeast at a temperature in the range of 33°F to 65°F for a period of time of 0.5 to 24 hours to reduce the stale flavor carbonyls, removing the yeast from the non-alcoholic beverage, and finishing and packaging the non-alcoholic beverage.

2. The method of claim 1, wherein the step of contacting the non-alcoholic malt beverage with yeast comprises mixing the beverage with a quantity of yeast containing greater than 20% yeast solids.

3. The method of claim 1, wherein the step of contacting the non-alcoholic malt beverage with yeast comprises mixing the malt beverage with a quantity of yeast to provide 50,000,000 to 400,000,00 yeast cells per ml.

4. The method of claim 1, wherein the step of contacting the non-alcoholic malt beverage with yeast comprises passing the malt beverage through a bed of inert particles having yeast cells adsorbed thereon, with said yeast cells having a concentration of 108 to 109 cells per ml of bed.

5. The method of claim 1, wherein the mixture of non-alcoholic malt beverage and yeast is maintained at a temperature of 33°F to 65°F for a period of 0.5 to 24 hours.

6. A method of producing a malt beverage having improved flavor characteristics and long-term flavor stability, comprising the steps of preparing a fully fermented malt beverage, contacting the fully fermented malt beverage with yeast for a period of time sufficient to reduce stale flavor carbonyls in the beverage, and thereafter removing the yeast from the malt beverage.

7. The method of claim 6, wherein the step of contacting the malt beverage with yeast comprises mixing the malt beverage with a quantity of yeast to provide a concentration of 50,000,000 to 400,000,000 yeast cells per ml.

8. The method of claim 6, and including the step of inoculating a bed of finely divided inert particles with yeast cells, contacting the yeast cells with wort and maintaining the wort in contact with said yeast cells for a period of time sufficient to obtain a yeast concentration of 108 to 109 cells per ml of said bed, removing said wort from said bed, and thereafter passing the malt beverage through said bed.

9. The method of claim 4, and including the step of flowing the malt beverage through said bed at a rate of 0.5 to 4 bed volumes per hour.