CA1083986A - Accelerated fermentation of lager-type beer - Google Patents

Abstract

ACCELERATED FERMENTATION OF LAGER BEER
Abstract A method of reducing the fermentation time required to produce a lager beer comprises conducting the fermentation at an elevated temperature of 60° to about 85°F with or without exogenous agitation while maintaining the dissolved carbon dioxide concentration in the fermentation liquor at about 1.5 to about 2.0 cc per cc of fermentation liquor by use of an overpressure of 2-20 psig of carbon dioxide.

Description

Specification :
The present invention relates to a method of reducing the fermentation time required to produce a lager beer -which comprises conduc~ing the fermentation at an elevated temperature of 60 to about 85F with or without exogenous agitation while maintaining the dissolved carbon dioxide concentration in the fermentation liquor at about 1.5 to about 2.0 cc per cc of fermentation liquor by use of an overpressure of 2-20 psig of carbon dioxide.
In the specification that follows, attention is directed to various references by number. A list of the references is included at the end of the specification.
Historically, there are two general methods of ferment-ing malt beverages. For the production of ale-type beers, ~ 15 a top-fermentation process is used which utilizes a species - of yeast whichtends to rise to the top surace of the fer-menting wort. The temperature during top-fermentation is con~entionally regulated at abou-t 15-20C (58-68F) through-out the most active period of fermentation. For the pro-duction of lager-type beers, a bottom-fermentation process is used which utilizes a species of yeast that remains more or less uniformly suspended, throughout the fermenting wort during active Eermentation, by natural agitation created by ascending CO2 bubbles (25), then settles to a more or less compact layer on the bottom of the fermentation vessel as fermentation reaches completion. The temperature during a ~`
; bottom-fermentation is conventionally regulated at about 10-15C (50-58F) during active fermentation (1, 2).
It is well known that if the temperature during bottom-fermentation is increased, the fermentation can be accelerated 1 .,~ .

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and the fermentation time substantially shortened. However, "-:
the beer so obtained has an undesirable winey flavor which is not typical of a lager beer (3-5). This winey off-flavor in high-temperature lager fermentations is related to in-- 5 creased amounts of beer volatile compounds. Vigorous exo- ;
genous agitation also can substantially reduce the fermenta- .
tion time of lager beer (4-6, 8, 16). However, this means of accelerating fermentation also has a detrimental effect : on the beer flavor which is related to an increased level of volatile compounds such as fusel alcohols (4-6, 8, 10, 15-17).
Furthermore, it is well documented that the use of higher temperatures (13, 18, 19) or exogenous agitation (16, 18) during bottom-fermentation results in excessive : .
yeast growth. Thus, the aforementioned techniques for shortening fermentation time, do so with the disadvantages of excessive yeast growth- and increased volatiles formation which is deleterious to lager beer flavor.
, It is an object of the present invention to disclose a method of reducing the length of time required for a bottom fer-mentation to produce a lager beer whi.ch comprises placing beer ~l wort in a fermentation vessel and fermenting the wort in said ;. vessel with yeast for about 50 to about 175 hours at an elevated temperature of 60F to about 85F while maintaining the dis-solved CO2 concentration in the fermenting wort at about 1.5 ., .
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3~86 "'~' ~' to about 2.0 cc per cc of the fermenting wort by use of a C2 overpressure in the vessel of about 2 to about 20 pslg.
It is known that fermenting beer is supersaturated -~
with CO2 uniformly throughout the body of fermenting beer during the active phase of conventional lager fermentations (24-26). It is also known that vigorous exogenous agitation eliminates this CO2 supersaturation (24). We have dis- ;:
covered that this supersaturation is maintained quite con-stant throughout the active period of fermentation (22).
There also is a direct relationship between the level of exogenous agitation and the degree of CO2 supersaturation maintained during lager fermentations (22). While there ;
are references in the literature (20, 21) that CO2 over-pressure represses yeast growth, we have discovered that it is not the CO2 pressure as such, but the dissolved CO
concentration in the fermenting liquid which determines `
the extent of growth repression (22).
We have discovered that if we maintain the concentration of the dissolved CO2 in the fermentation liquid at a level ~: .
approximating that found in a normal fermentation for a lager beer, we can employ temperatures higher than normal for a bottom ; fermentation to obtain a lager beer without an undesirable ,, j ~winey flavor. In order to maintain the desired level of dis-~- solved CO2, it is necessary as the temperature is increased to employ an increased overpressure of carbon dioxide. Pre-. .:

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ferably the overpressure is such that the dissolved CO2 level is maintained at about 1.5 to about 2.0 cc per cc of fermentation liquid. In the practice of the invention we have found that the combination of temperatures of 6C-85F, and appropriate carbon dioxide overpressures of 2-20 psig will maintain the dissolved carbon dioxide at the desired level and permit the fermentation to be completed in 50 to 175 hours. Especially preferred is the combination of temperatures of 60-75F and appropriate CO2 overpressures of 2~12 psig which maintains the dissolved CO2 concentration at the desired level and permits the fermentation to be completed in about 100 hours.
The proper choice of CO2 overpressure requires knowledge of the influence of both temperature and CO2 overpressure upon the degree of CO2 supersaturation which prevails during the active phase of lager fermentations. We have discovered the quantitative relationships of these fermentation parameters of temperature and CO2 overpressure upon the level of CO2 supersaturation, and thus we can calculate the CO2 overpressure necessary to establish the desired ; dissolved CO2 concentration during a fermentation at any temperature within the range of at least 57 to 72F.
We have further related the influence of the fermen-tation parameters of CO2 overpressure, temperature, and exogenous agitation level upon the dissolved CO2 concen-tration in lager fermentations.
We have found that, while the dissolved CO2 concentra-tion during active fermentation is influenced by both CO2 overpressure and fermentation temperature, the supersatura-tion is constant, regardless of the fermentation temperature ~0~398~

or C02 overpressure ~at least ~ithin the xange examined; 57-72F, and 0-16 ~;
psig respectively~. The dissolved C02 concentration is, of course, influenced inversely by temperature and directly by pressure. The d~ssolved C02 concen- -tration at saturation for a wide range of temperature and C02 pressure condi-tions is available in the literature (27). The dissolved CO2 level actually present in the fermentation is proportionately greater because of supersat-uration, and it is this degree of supersaturation which is constant regardless of temperature or C02 pressure. This is shown graphically in Fig. 1. ;~
~e have discovered that the degree of agitation controls the level of supersaturation and that there is a direct linear re~ationship between the degree of supersaturation and agitation as shown in Fig. 2.
Figure 3 graphically lllustrates the effect of dissolved C0 concentration on maximum yeast growth and volatiles concentration.
Thus, using the quantitative relationships we have discovered, it is possible to accurately predict the efect of altering any of three fermentation parameters--C02 overpressure, temperature, and agitation upon the dissolved C02 concentration prevailing during fermentation. For example, ~, if it is desired to shorten fermentation time by use of exogenous agitation, ... .
we can predit the effect of the selected level of agitation upon supersat-~1 20 uration, and thus we are able to ~alculate the C02 overpressure required to adjust the dissolved C02 concentration during the fermentation to the level which normally exists in a conventional lager ~ermentation.
There i5 increasing use o large, very deep f0rmenting tanks in : the brewing industry. The volatiles concentration is frequently less in the ` beer from these tanks than occurs , ~`

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in a conventionally fermented lager beer (7). This is a ;-result of excessive dissol~ed CO2 due to the much greater tank depth--often five times as deep as conventional lager ;~
fermentors. This increased dissolved CO2 concentration overrepresses yeast growth and concomitantly volatiles formation. Utilizing the quantitative relationships we have developed, the normal level of dissolved CO2 can be established by applying either the proper degree of exo-genous agitation or temperature increase, or both. This, as we have demonstrated will result in the proper amount o~ yeast growth and volatiles concentration. A further benefit will be shortened fermentation time, due to the accelerating effects of both agitation and increased temper-ature. ;
The necessary CO2 overpressure required to maintain the dissolved CO2 level in the fermentation liquid at the desired level can be calculated by the following formula in which the rate of agitation approximates agitation -;~ caused by the natural evolution of carbon dioxide:
Dissolved CO2 during fermentation = 1.5 x dissolved C2 at saturation.
Thus, by dividing the desired dissolved CO2 ~oncentration during fermentation b~ 1.5, the saturation level of dissolved C2 is determined. With both the fermentation temperature and the saturation level of dissolved CO2 known, the required C2 overpressure is obtained from either the literature (27) or Fig. 1, at 33 rpm. Since the effect of the level of agitation upon supersaturation is known, these conditions of temperature and CO2 overpressure will result in the desired CO2 level.

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A series of fermentations were run to demonstrate the utility and effectiveness of the invention. The fermenta-tion vessel used in the experiments was a 130-liter stain-less steel vessel with a working capacity of 100 liters, cylindrical, about 33 inches high and 17 inches inside diameter. It was equipped in conventional fashion, i.e.
with pressure cap, temperature and pressure gauges, vapor ; inlet and exit lines, and liquid discharge spigot at the bottom. It was provided with an external cooling/heating jacket and with turbine-type impellers and baffles. The arrangement permitted precise control of agitation, tempera-ture, and headspace pressure over a wide range.
The concentration of volatile components of fermented beers was determined by conventional gas chromatographic , 15 techniques, either by analyzing headspace gas above an enclosed sample (see "Gas Liquid Chromatography (GLC) Tests", infra) or by analyzing a carbon disulfide extract o the beer. The yeast concentration was determined both ; by cell count with a haemocytomer and by dry weight ;
determination of the centrifuged yeast. The completion o a fermentation was determined by two widely accepted criteria: the decrease of diacetyl concentration to 0.10 ppm, estimated by U.V. spectrophotometry, and by the disappearance of ermentable sugars, estimated by high pressure liquid chromatography.
A series of Eermentations, Examples 1-7, were run in the aforesaid 100-liter fermentor employing a conventional commercial wort, i.e. a 14.1 Plato wort which was prepared using a 55/45 malt-adjunct ratio, with the adjunct being 65% commercial corn grits and 35% commercial brewers' syrup.

General Procedure Used in ~xamples The conventional commercial wort, both aerated and pitched with lager yeast in production equipment in the conventional manner, was aseptically transferred from a 1000-barrel commercial fermentor to the CO2-packed, 100-liter fermentor 20 hours after pitching. This assured that the procedures prior to ~ermentation did not deviate from conventional comm~ercial practice. The 20-hour residence in the commercial fermentor prior to transfer corresponds ~-~
approximately to the yeast lag phase, during which little yeast growth takes place, but during which the oxygen, added during aeration, is absorbed, preparatory to growth. If . . , this delay in transfer had not been used, CO2 pressurizing in the 100-liter ermentor would have had to be delayed to assure this oxygen absorption.
Agitation was maintained at 33 rpm in the 2-foot deep, 100-liter fermentor, since it has been previously established ... .
that this mixing speed duplicated the agitation conditions .:, , normally occurring as a result of CO2 evolution by yeast during fermentation in our 8-oot deep commercial fermentors.
Fermentation was judged completed when both carbohydrate ` assimilation ceased (at an acceptably low residual level) and diacetyl concentration decreased to 0.10 parts per million. Both of these conditions are conventional criteria of the final completion o lager fermentation.
At the completion of fermentation, the raw beer was withdrawn, clarified, and bottled, and analyzed as described elsewhere.
The following e~amples illustrate without limiting the invention.

XS~3~6 Example 1 This example is a control. In it, conventional fer-mentation conditions are used. These conditions give an acceptable raw beer. Note that a total of 196 hours were required to complete the fermentation.
One hundred liters o~ the conventional wort, aerated and pitched at about 10 million cells/cc, were fermented at a constant 57F with low level agitation (33 rpm) and no CO2 overpressure. ~he yeast concentration reached a ; 10 maximum of 5.77 grams/liter (dry weight basis) and 60 million cells/cc. About 160 hours were required to erment : ~ .
the available carbohydrates and an additional 36 hours ,,?, (approximately) were required to reduce diacetyl to 0.10 ppm. The volatiles concentration expressed as the total , 15 area of the component peaks from the gas-liquid-chromato- ,-', graphic (GLC) analyses, relative to the peak area of an internal standard taken as 100, was 904 tby analyzing CS
extract of the beer) and 648 (by analyzing headspace ., ~. .
;.~ vapors over the beer).
, 20 Example 2 This example is another control. It is like Example 1, except that the temperature was increased to 72F, to determine whether the increased temperature would shorten fermentation time while giving an acceptable product. As shown, the time was decreased, but the product was unaccept-able.
One hundred liters of the conventional wor*, aerated and pitched at about 10 million cells/cc, were fermented at a constant 72F with low level agitation (33 rpm) and no CO2 overpressure. The maximum yeast concentration - _g_ ~3~

reached 6.03 grams/liter (dry weight basis) and 69 million cells/cc. About 90 hours were required to decrease the diacetyl to 0.10 ppm and another 10 hours were required to complete fermentation of the available carbohydrates, ~or a total of 100 hours. Volatiles contentt as total relative GLC peak area, was 956 (CS2 extract) and 752 (headspace) compared to the internal standard of 100. The data in the table show that the high temperature of Example 2 decreased the fermentation time but increased the volatiles content, relative to Example 1.
Example 3 One hundred liters of the conventional wort, aerated and pitched at about 10 million cells/cc, were ermented at a constant 72F, 33 rpm agitation, and 14.9 psiy CO2 overpressure. The yeast concentration reached a maximum of 5.37 grams/liter (dry weight basis) and 53 million cells/
cc. Ninety hours were required to assimilate all ferment-able sugars and another 5 hours (for a -total of 95 hours) to reduce diacetyl to 0.10 ppm. Volatiles content, as total relative GLC peak area, was 820 (CS2 extract) and 298 (headspace). Example 3 demonstrates that in the presence of about 15 psig CO2 overpressure the volatiles formation normally accompanying a fermentation run at this temperature has been overrepressed without altering the accelerated fermentation rate.
Example 4 This example is another control and the conditions of this fermentation were designed to duplicate conventional commercial lager fermentation characteristics and the characteristics of the resultant raw beer.

~3g86 One-hundred liters of the aforementioned commercial wort, handled in the manner previously described, were fermented at a constant 59F, with no CO2 o~erpressure.
A constant low level (33 rpm~ of agitation was applied to duplicate natural agitation conditions in the commercial fermentor. The dissolved Co2 concentration in the fermen-tation liquid was 1.52 cc of CO2 per cc of liquid.
; About 172 hours were required to decrease diacetyl to 0.10 ppm and an additional 6 hours were required to complete fermentation of available carbohydrates. Thus a total of 178 hours (7.4 days~ was required to reach the , end of fermentation using the criteria previously described.
~east concentration reached a maximum of 5 9 grams/
liter (dry wei~ht basis) and 58 million cells/cc. The total volatiles concentration, as determined by gas-liquid ~il chromatography, was 872, relative to the reference standard ; used in the analytical method.
The fermentation time required and yeast growth and volatiles concentration are typical of our raw lager beer.
Example 5 The conditions of this fermentation were designed to demonstrate the influence of fermenting at a temperature greatly in excess of normal lager practice.
One-hundred liters of the aforementioned commercial wort, handled in a manner previously described, were fer- ;~
mented at 72F with no CO2 overpressure. A constant agitation of 33 rpm was applied to duplicate agitation conditions occurring naturally in the commercial fermentor.
The dissolved CO2 concentration in the fermentation liquid was 1.30 cc of CO2 per cc of liquid.

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About 85 hours were required to ferment the available carbohydrates and another 4 hours to decrease diacetyl to 0.10 ppm~ Thus the total fermentation time, based on the ;
pxeviously described criteria, was 89 hours (3.7 days).
Yeast growth reached a maximum of 6.45 grams/liter dry weight and 77 million cells/cc. Total volatiles con-centration, relative to the GLC reference standard, was 950.
Thus while the increased fermentation temperature .~:
shortened the time required for fermentation by 50%, the yeast growth and the volatiles concentration were increased ; to a level substantially in excess of our raw lager beer.
Example 6 The conditions of this fermentation embody our inven-tion. It is designed to demonstrate that with the use of the proper level of CO2 overpressure, the desired dissolved C2 concentration can be maintained and a fermentation can be run at a temperature far in axcess of accepted lager fermentation practice, without the usual deleterious effects of excessive yeast growth and volatiles formation of a high-temperature fermentation, while still achieving the shortened fermentation time resulting from the increased temperature.
One-hundred liters of the aforementioned commercial wort, handled as previousl~ described, were fermented at a constant 72F, and a constant CO2 overpressure of 8 psig.
A constant agitation level of 33 rpm was used to duplicate the agitation conditions occurring naturally through CO2 evolution in the commercial fermentors. The dissolved CO2 concentration of the liquid was 1.88 cc of CO2 per cc of ~t)83~86 fermentation liquid.
About 93 hours were required to decrease diacetyl to ~ ~-0.10 ppm and another 2 hours were required to complete fermentation of available carbohydrates. Thus a total of 95 hours (4.0 days) was required to reach the end of fer-mentation, based upon the criteria previously described.
Yeast growth reached a maximum of 5.9 grams/liter, ~
dry weight and 59 million cells/cc. The total volatiles ~ ;
concentration, relative to the GLC reference standard, was 820.
Thus the application of the proper CO2 overpressure .. ~ .
at this elevated temperature repressed both yeast growth ` and volatiles formation such that they were typical of our conventional raw lager beer as found in Example 4, while maintaining the decreased fermentation time of the high-temperature fermentation of Example 5.
Example 7 The conditions of this fermentation were designed to demonstrate our discovery that the repression of both yeast growth and volatiles formation are directly related to the dissolved CO2 concentration which is effected by the amount of CO2 overpressure applied.
One-hundred liters of the aforementioned commercial wort, handled in the manner previously described, were fermented at a constant 72F with a constant CO2 over-pressure of 14. A constant agitation level of 33 rpm was maintained, as previously described. The dissolved CO2 concentration of the liquid was 2.35 cc of CO2 per cc of beer. !
A total of 102 hours (4.25 days) was required to reach 3~6 '', the end of fermentation, based upon the criteria previously described. ;
Yeast growth reached a maximum of 5.5 grams/liter, dry weight, while total volatiles concentration, relative to the GLC reference standard, was ~67. As a result of the low volatile concentration the flavor was unacceptably bland for a typical lager beer.
Thus, the application of excessive CO2 overpressure at this elevated temperature overly repressed both yeast growth ; 10 and volatiles formation, as compared to Example ~, which exemplifies a conventional lager fermentation and raw beer.
The decreased ~ermentation time was typical of this temperature.
The pertinent data for the fermentations described in Examples 4-7 i5 shown in Table I.
Note that in all examples run at the elevated tempera-ture of 72F, the total fermentation time (the longest time taken for satisfying the two criteria of end of fermentation) was far less than in Example 4, run at the lager ~ermentation temperature of 59F.
Note the inverse relationship between the dissolved C2 concentration and both the maximum yeast growth and the volatiles concentration. The data is graphically presented in Fig~ 3. Thus, the greater the dissolved CO2 concentration, the less the maximum yeast growth and the volatiles concen-tration. Note that this relationship is true of dissolved C2 concentration in all cases and not of the level of CO2 overpressure. This demonstrates the validity of our discovery that it is the level of dissolved CO2 which is paramount in controlling yeast growth and volatiles concentration; CO2 ~3g~
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overpressure is -the means of adjusting the dissolved CO2 concentration to the requisite level. `
Knowledge of the influence of fermentation temperature, agitation, and CO2 overpressure upon dissolved CO2 levels -~
under supersaturated conditions is important for determininy the level of CO2 overpressure necessary for properly repress-ing yeast growth and volatiles formation to the amounts prevailing in the conventional lager fermentation.
TABLE I ~ ;
~xamples _ 4 5 6 7 ~
Temperature (F) 59 72 72 72 ;
Agitation (rpm) 33 33 33 33 C2 Pressure (psig) 0 0 8 14 Yeast Dry Weight (g/l) 5.9 6.45 5.9 5.52 Dissolved CO2 Concentration 1.52 1.30 1.88 2.35 (cc/cc beer)*

End of Sugar Assimilation 178 85 95 80 Fermentation Time (hours) to 0.10 ppm Diacetyl 172 89 93 102 ;
Total Volatiles (Relative GLC Peak Area**) 872 950 820 667 :
* Value prevailing during active ermentation.
** Area relative to internal standard as 100.
A CO2 overpressure as low as 2 psig used in conjunction with an appropriately elevated temperature (within the scope of this invention) will have the beneficial result of pro-ducing an acceptable beer, while reducing fermentation time.

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C2 overpressures in excess of this lower limit are likewise ~ ;
suitable, and will depend upon the temperature being employed assurning the rate of agitation is constant. Generally over-pressures in the range of 2-20 psig are preferred.
The CO2 overpressure is preferably added at the end of the yeast lag phase. Additionally, and/or as a partial alternate, the CO2 overpressure used can suitably be in -part that normally and autogenously developed during the fermentation. It is retained within the vessel and in the overhead space/ but may be vented continuously or from time to time if desired, while retaining the desired overpressure.
The CO2 overpressure on the face of the fermenting liquid, of course, results in an increase in dissolved CO2 concentration in the body of the liquid, and it is this dissolved CO2 which provides the beneicial effects.
Conventional fermentation temperatures for lager-type beers in the United States run typically in the range of 54-57F. We know from our work that an increase in CO2 concentration or the use of CO2 overpressures will not reduce fermentation times when used with such temperatures.
Thus, we recommend temperatures at least as high as 60F.
Temperatures as high as 85F can be used. Thus, our broad operative temperature range is 60-85F. We prefer, however, to use a temperature within the narrower range of 60-7SF.
These higher temperatures must be accompanied by CO2 overpressures to maintain the dissolved CO2 concentration at the desired levels of 1.5 to 2.0 cc of CO2 per cc of ~, beer. Otherwise, the beer will have a winey and/or estery taste and flavor.
; 30 The fermentation process is exothermic, and the fer-A ~

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menting liquor will warm up. In conventional fermentations, this heat is removed by refrigeration. In the instant inven-tion refrigeration may still be found desirable, but only for the purpose of keeping the ~ermenting wort within the higher temperature range. In other words, not as much heat is taken out in our process as in conventional fermentations. `
On the other hand, external heat may be applied if circum-stances require.
The upper temperature limit is the temperature at which the yeast metabolism is significantly altered.
Depending on conditions, this temperature may be around ;
85F.
It is an object of the invention to decrease fermen-tation time. In accomplishing this by increasing fermen-tation temperature and maintaining the dissolved CO2 con-centration at the desired level by CO2 overpressure, we do not aim so much at a specific time as at a reduction in the ; time that would ordinarily be required if our invention were not used. Thus, in a fermentation that might ordinarily ; 20 require 8 days to complete, the use of our invention could be expected to reduce fermentation time to 4-5 days. On '~
the other hand, a 10-day fermentation mi~ht be reduced to 5-6 days, and so on. The reason for the variation is, of course, the variation in fermentation equipment, wort characteristics, brewhouse schedules, and so on. Generally, however, the use of our invention will reduce fermentation time for a given set of conditions by 25-75%, more or less.
Normally a fermentation employing our invention will be complete in 50 to 175 hours. This time saving has the effect of multiplying the capacity of the equipment by the ; ~B3986 said percentage factor, obviously with a concomitant saving in the cost of capital equipment.
Completion of Fermentation, Product Examination Conventional techniques were used to determine com-pletion of fermentation, viz., disappearance of sugars and disappearance of diacetyl. Diacetyl is an undesirable buttery-tasting material which is initially formed by the fermentation process. It reaches a peak, then gradually disappears. Amounts in excess of 0.10 ppm are generally considered objectionable in most breweries, and, therefore, the fermentation is continued at least to approximately this end point. Thus, the fermentation is not considered complete until the last to occur of two events, (a) sugar disappearance and (b) diacetyl drops to about 0.10 ppm.
Comment~ the value of 0.10 ppm cannot by any means be con-sidered critical. It may be somewhat higher or lower, depend-ing on local brewing practice. The value is, however, typical, and we prefer it.
Completion of fermentation does not necessarily mean that the product is a good beer. Thus, in Example 2, com-pletion of fermentation gave a beer with an excessive amount of higher alcohols and higher esters. (Note volatiles of 956 in the CS2 extract.) Such beers usually have a winey character. And, as a matter of fact, we have been able to show in many cases that such alcohols and esters are present in runs like those of Example 2 in quantities higher than those of conventional fermentations and those af the instant invention. Such analyses have been made by techniques standardized in the laboratories of The Miller Brewing Company and involve extraction using CS2, and gas-liquid 1~3~6 chromatography, as described elsewhere herein~ The quantity extracted in a given fermentation product is compared with a norm previously established as a suitable standard. The runs made using ~his invention generally give values that do not exceed this norm. However, it is difficult i~ not impossible to state any given limits for volatiles (i.e., higher alcohols and esters, etc.) for any given run.
Although the ultimate test is taste, as determined by an experienced and competent taste panel, GLC data are known to correlate well with panel data, and are more readily accessible. Our conditions of temperature and CO2 over-pressure as above stated will inherently give a beer product that will provide suitable taste as determined by such a panel.
The higher alcohols and higher esters above referred to ("winey" or "estery" materials) are known by various names, e.g. volatiles, fusel oils, etc. They are tolerated or may even be useful in ales or wines, but in general, they are desirably minimized in lager beer. Among these materials we have identified n-propyl, iso-butyl, iso-amyl, and phenethyl alcohols; ethyl, iso-propyl, iso-amyl and phen-ethyl acetatesi acetaldehyde; and ethyl propanoate, hex-anoate, and octanoate. Additionally, there are several unknows that we have not identified. In the aggregate, the formation of these materials is suppressed in fermen-takions at the higher temperatures of this invention by maintaining the level of dissolved CO2 in the range herein described. Iso-amyl alcohol and ethyl acetate are apparently the major components of these volatiles. The quantities of both are strongly suppressed by use of CO2 overpressure, 3~36 although they both still remain the major components of the resulting volatiles.
After fermentation is complete, the green (raw) beer product is recovered and finished by conventional pro-cedures.
Gas Li uid Chromatogra h ~GLC) Tests q P Y
These tests (for "winey" higher esters and higher alcohols) are designed to establish that in the practice of this invention these substances approximate (or at least do not exceed) in kind and amount, like materials in beer brewed by standard processes.
The basic test technique is well known, and for our purposes certain modifications have been introduced in view of the particular compounds to be identified. For example, the identifying "artifact" must be selected so that it falls in a valley between peaks of known components.
For examination of headspace volatiles, for example, a suitable artifact is m-xylene, which falls between iso-amyl -alcohols and lso-amyl acetate. 3 The gas chromatograph used was a Hewlett-Packard, Series 7621A with dual flame ionization detectors. A temper-ature of 270C was used for both the detector and injeckor.
; A dualcolumn was used, 10 ft. by 1/8 inch stainless steel, packed with 80-100 mesh Porapak Q (a commercially available sorbent). Nitrogen was used as the carrier gas, at an inlet pressure of 78 psi and a flow rate of 55 ml/min.
~` Pre aration of Sam~le for Injection -P
After chilling for one hour at 0C 50 mls. of beer are gently measured and poured into a 7 oz. beer bottle containing 20 gm. of anhydrous sodium sulfate (to aid in ~L~3~3~86 "salting out" the vapors). A Neoprene crown insert is placed over the top and the bottle is crowned with a beer cap (insert removed) which has a small hole for sampling purposes. 10 ml of a standard m-xylene solution (1 ml.
diluted to 100 mls, with 95% ethanol) is added. The sample is warmed in a 50C water bath for 10 min., shaken 30 sec., and kept at 50C for 20 min. The bath is then cooled to 25C (10-15 min.). The sample is then kept in the dark -overnight at 25C to equilibrate. Two individual samples of the same beer comprise a replicate analysis. An 8 ml.
vapor sample is obtained in a 10 ml. gas tight syringe ~after gently pumping five times) by drawing in 9 ml. and expelling 1 ml. The sample is then injected into the ~ , chromatograph inlet.
The apparatus automatically prints out a chromatogram showing the individual components as peaks. The area under a given peak is proportional to the quantity of the component.
For a more exact estimation, the area can be compared to the area of the artifact, for that amount is, of course, ~ 20 exactly known.
; While in the foregoing description we have described examples utilizing specific conditions, it is to be under-stood that maintaining the dissolved CO2 concentration at the desired levels in the beer under accelerated fermentation conditions by varying the temperature, the agitation or the C2 overpressure during fermentation is within the spirit and scope of our invention.

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_

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14~ Kamiyama, S., and Nakagawa, A., Brewers Digest, Feb.
1968, p. 60.

15. Szlavko, C. M., _. Inst. Brew., 79, 283 (1973).

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~ 3~8~ ~

:::

21. Drews, B., et al., Brauerei, Wissensch. Beil., 7, 111, (1954). `

22. Rice, J. F., Helbert, J. R., and Garver, J. C., Amer. ~ `
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, ~
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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of reducing the length of time required for a bottom fermentation to produce a lager beer which com-prises placing beer wort in a fermentation vessel and fer-menting the wort in said vessel with yeast for about 50 to about 175 hours at an elevated temperature of 60° F to about 85° F while maintaining the dissolved CO2 concentration in the fermenting wort at about 1.5 to about 2.0 cc per cc of the fermenting wort by use of a CO2 overpressure in the vessel of about 2 to about 20 psig.

2. The method of claim 1 in which the temperature is 60° F
to about 75° F and the CO2 overpressure is about 2 to about 12 psig.

3. The method of claim 1 in which the temperature is about 72° F and the CO2 overpressure is about 8 psig.

4. The method of claim 1 in which as the temperature is increased, the overpressure of CO2 is also increased to maintain the dissolved CO2 concentration at the desired level.