GB2298651A - Propagation of brewing yeast under aerobic conditions - Google Patents

Description

IMPROVEMENTS IN AND RELATING TO BREWING/YEAST PROPAGATION This invention relates to the propagation of yeast and to brewing. It is primarily, but not exclusively concerned with the propagation of yeast for use in brewing, wine production and other processes, and to brewing using specially propagated yeast.

In brewing raw materials are placed in a fermentation vessel to be fermented into an alcoholic product such as beer. Yeast which is initially added to the fermentation vessel multiplies by a factor of approximately 3 to 5-fold in mass. Yeast produced in one fermentation is recovered at the end of that fermentation and is used to pitch one or more subsequent fermentations. Excess yeast is disposed of. In principle, this cycle can be continued indefinitely and in some traditional breweries this is the case. However, in modern breweries it is usual to place a limit on the number of serial fermentations in which individual yeast lines are used.

The reasons for the limitation of serial fermentations are mainly related to microbiological purity. With each serial fermentation there is a risk that the yeast crop will become contaminated with other microorganisms. Of particular concern is the potential for cross-contamination where several different yeast strains are used within a single brewery. In addition, it is possible that the properties of individual strains may change during the course of several fermentations. For this reason it is usual to replenish yeast with new lines of guaranteed purity and identity.

Propagation of yeast for supply to a brewery fermentation vessel begins in a laboratory and involves small-scale cultivation of pure yeast taken from laboratory stock cultures. Sequential sub-culturing into progressively larger volumes of growth medium produces sufficient yeast to transfer from the laboratory into a brewery for further propagation to occur. In the brewery, wort is used as a growth medium and a regime is usually employed of sequential cultivation of yeast in progressively increasing batch sizes. In the majority of breweries a two stage propagation system is used. A first vessel, a seed propagator, is typically of approximately l.0m3 capacity. A second vessel, the propagator, is usually 5-10 fold bigger than the seed propagator (say 4 to 8m3).

In design and operation, traditional brewery propagators are little more than under-sized fermenting vessels. There is a strong view amongst brewers and those skilled in the art of brewing that the new yeast should be grown in a manner in which the physiological state of the yeast at the end of propagation should be similar to that of yeast cropped at the end of fermentation. To this end growth during propagation is limited in two ways.

Firstly, wort is traditionally used as the growth medium for propagation. The high sugar concentration present in wort results in the yeast having what is termed "catabolite repressed" or "fermentative" physiology. One of the consequences of this is that the yield of new yeast mass as a ratio of the sugar utilised is always low and most of the supplied sugar is converted into ethanol.

This contrasts with Bakers yeast propagation where the sugar is fed into the growth vessel over a period of time and at a rate at which it is immediately utilised by the yeast. In this case, the actual sugar concentration in the propagator is always very low and such yeast has a physiology which is termed "catabolite derepressed" or "respiratory". Yields from Bakers yeast propagations are very high and little or no ethanol is generated.

Secondly, in a traditional brewery propagator, yeast growth is limited by restricting available oxygen. Brewery fermentation is traditionally considered to be an anaerobic process. However, this is a misconception. During fermentation brewing yeast does require some oxygen for new growth of yeast and this is supplied in a single initial dose with the wort in the fermenter. Propagations are operated under "semi-aerobic" conditions by the intermittent supply of air. This stimulates growth to the extent that typical yields from a traditional propagator are in the order 6 of 60 - 80 x 10 cells/ml. This compares with a yield from a traditional fermenter of approximately 40 - 60 x 106 cells/ml.

Since there is a prejudice amongst those skilled in the art that propagation should be carried out under conditions which mimic those of fermentation, propagation is, as discussed above, carried out as a semi-aerobic process with severely restricted oxygen supply.

Traditional propagators aim to generate yeast which has similar physiology to pitching yeast such that the profile of the first fermentation and resultant beer are standard. Hence the provision of limited quantities of oxygen. It is common for the first fermentation to be slow and for the beer to be non-standard. This non-standard beer is often blended away. It is common practice when using newly propagated yeast for 2 or 3 fermentation cycles to be required before standard behaviour is observed. Since any yeast line is used typically for only 15-20 cycles in total, the ratio of "good" fermentation runs of a fermentation vessel to "poor" runs, with beverage that needs to be blended, is about 5 or 6 to 1. Up until now brewers have thought that this is fine. However, we do not accept this traditional thought.We believe that having so many brews which cannot be used directly is wasteful of the operational capacity of the fermenter. It would be better if there were fewer, or no, poor quality brews at the start of a fermention run cycle of a fermenter.

We believe that the yeast propagated by the traditional methods discussed above is of poor quality: the yeast does not ferment wort in a fermentation vessel with the vitality which it might have.

Process times in traditional propagators are in the region of four to seven days.

A further development has been the increase in volume of fermenters. In traditional breweries these are usually in the range 100 - 500 brl (16-60m3).

These quite small fermenters can be serviced adequately by relatively unproductive propagators. In modern breweries, fermenter volumes have been increased to 1000-3000 brl (160-490m3). Conventional propagators cannot supply sufficient yeast to pitch these large vessels. For example, a 50 brl propagator may produce 6 a terminal yeast count of 70 x 106 cell/ml which may be pitched into 1000 brl or wort. The scale up factor is 1:20 and therefore, the predicted pitching rate in 6 fermenter would be 3.5 x 106 cells/ml. This pitching rate is very low, possibly only 20-30% of the desired rate, and it would be predicted to give a slow and non-standard fermentation. It is usual to undertake a special regime with the first F.E. in order to remedy this.Effectively this means that the first fermentation in a F.E. is still part of the yeast propagation cycle.

It is possible to use more than one propagator to pitch into the initial fermenter. This will obviously increase the amount of yeast present, and increase the pitching rate.

However, the problem of underpitching in the first fermentation is usually dealt with in a number of other ways. In some cases it is ignored and it is simply accepted that the first fermentation will be atypical.

Alternatively the first pitch can use a small or underfilled fermenter. However, in these solutions the first fermentation simply represents a further stage in propagation, and therefore, both options are wasteful, and the second may not be practical. Although, as a third option, it is also possible to use larger propagators this is impractical since it is wasteful in terms of wort and would represent an unacceptable level of dilution when pitching into the first fermentation.

It is an aim of the invention to address, and alleviate at least in part, some of the problems discussed in the foregoing.

According to a first aspect the invention consists in a method of propagating brewing yeast in substantially aerobic conditions.

Preferably the conditions are such that the yeast propagates with catabolite repressed (or fermentative) physiology.

The yeast is propagated on a feedstock that has an excess of sugar. Preferably wort is used as the feedstock.

Preferably the method is particularly applicable to brewing yeast for brewing beer.

Preferably oxygen is available to, or supplied to, the yeast at all times, or substantially all times.

The oxygen may be provided in air.

Preferably the yeast is propagated in a propagating vessel. The vessel may be aerobic. The vessel may be constantly aerobic through propagation.

Preferably the propagator is fed continuously with oxygen, or an oxygen containing gas mixture such as air.

By propagating in aerobic conditions, we have found that we can obtain yeast that is less stressed than the yeast which issues from conventional propagators. Yeast which is less stressed should produce a more vigorous and consistent first fermentation. This will reduce the number of "poor" initial fermentations that need blending. Our second, or even first, fermentation following inoculation of yeast into a fermenter may be within permissible standards of the desired beverage.

This increases the efficiency of the fermenter by perhaps 10, 15, or even 20%.

Preferably propagation occurs at relatively high temperatures. Preferably propagation occurs between 100C and 300C. Most preferably the range is between 200C and 25C or 300C.

Preferably oxygen is supplied to the yeast or a yeast-containing media or both. The oxygen may be stirred in, shaken in, agitated with, or bubbled through the yeast and/or media.

Preferably the propagator is provided with mixing means. This may be provided to ensure that oxygen is transferred to the yeast to maintain aerobic conditions. The mixing means may be an impeller.

Alternatively mixing could be provided by bubbling oxygen (or air) through the contents of the propagator.

The invention usually produces more yeast than would be produced in an equivalent system operated under the traditional method. There may be an increase of in production of yeast of two, three, four, five or more times over traditional methods.

The method may produce yeast of better quality.

For example yeast so produced may be less stressed. It may confer other advantages such as shorter propagation times for an equivalent mass or quantity of yeast. In one example we achieved a process time for propagation of about 48 hours and found a yield of about 150-200 x 106 cell/ml. This is a yield of 2-3 times more than traditional propagators. Furthermore, a traditional propagator takes about 4-7 days to complete the propagation process. We have therefore halved that time.

Alternatively, yeast propagated produced by the method may simply be better. It may be more robust; more physiologically suited for producing beer or other alcoholic beverages. Other quality improvements in the yeast which may result from the method are better membrane competency, better vitality and better fermentation performance. For example, as discussed earlier, the time taken for propagation of a quantity of yeast may be two-thirds, a half, a third or a quarter of the time taken for propagation according to traditional methods. This could cut down the propagation time from about five days to two days.

A further advantage of the invention is that in producing yeast which is more suitable for pitching into wort, we can pitch with the first brew.

According to the second aspect of the invention we provide a propagator vessel for propagating yeast in substantially aerobic conditions.

Preferably the propagator has oxygen supply means adapted in use positively to supply oxygen to a yeast growth medium in the propagator. A flow meter may be provided to monitor the amount of oxygen being provided.

Preferably the propagator has agitator means or mixing means adapted in use to mix a yeast growth medium in the propagator. The agitator or mixing means may comprise a rotatable member, for example a paddle.

Preferably the propagator has a temperature sensor.

Preferably the propagator has an oxygen level sensor.

Preferably a controller is associated with the propagator and controls its operation in response to signals received from sensors.

Preferably the vessel has oxygen supply means.

The oxygen supply means may be adapted to supply oxygen or an oxygen containing gas mixture such as air.

According to a thid aspect the invention comprises the use of a propagator according to the second aspect of the invention by a brewer to grow yeast for the production of beer, or wine.

Preferably the use of the propagator according to the third aspect of the invention is done in combination with yeast that is a brewers yeast. A brewer will know perfectly well what yeasts he is using, and has used to brew his own beer. Furthermore, the National Collection of Yeast Cultures, in Norwich, produces a publication, the Catalogue of Cultures, which, identifies a large list of yeast strains that are used for brewing beer and other alcoholic beverages.

According to a fourth aspect of the invention we provide yeast that has been propagated under substantially aerobic conditions in accordance with the first aspect of the invention.

Preferably yeast is produced in catabolite repressive or fermentative mode. Alternatively we may grow the yeast in its oxidative or derepressed mode.

According to a fifth aspect the invention consists in a method of making a fermentation product using yeast according to the third aspect of the invention.

The fermentation product may be beer, lager, ale, wine or the like.

The present invention may be particularly applicable to the large-scale production of beer and other beverages in a brewery.

According to a sixth aspect of the invention we provide a method of brewing beer comprising propagating yeast in a propagator, inoculating a fermentation feedstock (wort) provided in a fermentation vessel with yeast from the propagator, and fermenting wort in the fermentation vessel to produce beer; the method further comprising the step of producing the inoculated yeast in the propagator in conditions that are aerobic and that are arranged such that the yeast is propagated with catabolite repressed activity.

It will be appreciated that "beer" means beer, lager, ale, porter, cider, stout and the like, or indeed any alcoholic beverage.

Preferably the method comprises continuous or substantially continuously supplying oxygen to the propagating yeast during the propagation process.

Preferably the supply of oxygen to the propagating yeast is an active supply, rather than a passive supply.

According to a seventh aspect of the invention we provide a method of reducing the process time for propagation of brewing yeast comprising propagating the yeast under aerobic conditions, and ensuring that the conditions are such that the yeast has catabolite repressed, fermentative phsyiology during propagation.

Preferably the method comprises propagating the yeast in wort.

According to an eighth aspect of the invention comprises the use of yeast propagated in aerobic conditions with catabolite repressed activity in the inoculation of wort for brewing beer.

According to a ninth aspect the invention comprises the use of yeast propagated in aerobic conditions, with catabolite repressed physiology, in inoculating wort for the preparation of a fermentation brew in a fermentation vessel in order to increase the efficiency of use of the fermentation vessel.

According to a tenth aspect the invention comprises an improvement in a method of brewing beer where an initial propagation yeast supply is introduced to a first fermentation vessel and a first beer is brewed in the fermentation vessel and yeast produced during the brewing of the first brew of beer is used to pitch a second brew of beer in a fermentation vessel, and yeast grown during that brew is used to pitch a further brew of beer, and so on; the improvement comprising reducing or minimising the need to blend sub-standard beer produced by the first brew, and possibly the second brew, by the use of yeast that has been propagated in aerobic conditions in the preparation of the initial propagation yeast supply for inoculation into the first fermentation vessel.

Preferably oxygen us supplied to the propagating yeast substantially continually during its propagation.

Preferably the conditions during propagation are such that the yeast has catabolite repressed, or fermentative, activity during propagation.

The same fermentation vessel may be used for successive brews, or another may be used.

According to an eleventh aspect of the invention we provided a method of reducing the time to brew a batch of beer comprising used yeast that has either: (a) come from a propagator which has propagated the yeast in aerobic conditions; or (b) has a propagator source in accordance with (a) at some point in its past reproduction cycle.

The yeast of condition (a) is preferably supplied with oxygen, for example in the form of air, continuously, or substantially continuously, when it was being propagated.

The conditions in the propagator of condition (a) are preferably such that the yeast has catabolite repressed, or fermentative, activity, preferably for the majority of, or substantially whole of, its propagation in the propagator.

According to a twelfth aspect of the invention we provide beer or alcoholic other beverage that has been made by a method which uses any of the foregoing inventions.

An example of the present invention will now be described with reference to the following drawings of which: - Figure 1 shows a schematic representation of an aerobic propagator vessel; and Figure 2 shows a graph showing the growth of yeast in the aerobic propagator of Figure 1.

Figure 1 shows an aerobic propagator vessel 10 comprising a cylindrical stainless steel tank 12 of about 800 litres volume. The tank is surrounded by a stainless steel jacket 14 which defines a cylindrical space 16 surrounding the tank 12. A heat transfer medium, for example ethylene gylocol, can be caused to flow in the space 16, for example by a pump 18.

A temperature sensor 19 is provided (or several temperature sensors), and appropriate valves in the flow passageway of the coolant liquid in the attemperation circuit. When yeast grows in the vessel it gives off heat and this is extracted by the heat transfer medium so as to control the temperature of the liquid in the tank 12. A controller C, such as a computer, controls the operation of the pump 18 and associated valves.

A stirrer, or agitator, 20 is provided in the tank, towards its bottom end. The agitator 20 comprises blades or paddles 22 mounted on a central axle member 24 and rotated angularly. An external motor 26 is provided to operate the agitator. The controller C controls the operation of the agitator.

An oxygen pipeline 28 extends into the tank 12, towards the bottom of the tank and supplies an oxygen release head 30. The oxygen release head is a sparger. Oxygen is, in use, released from the sparger 30 and dissolved in the liquid that is in the tank 12. The supply of oxygen to the sparger 30 is controlled by a suitable pump (not shown) which is in turn controlled by the controller C. A dissolved oxygen tension sensor (DOT sensor) 32 is also provided to monitor the oxygen in the liquid in the tank. The sensor 32 sends its signals to the controller C. Again suitable valves under the control of the controller are provided.

A wort introduction pipeline 34 is provided. This is, in this example, at the base of the vessel 12. A valve 36 controls the addition and removal of liquid from the tank 12. A heat exchanger 38 is provided associated with the pipeline 34 and, in use, can sterilise wort as it is introduced into the tank 12.

In addition to supplying oxygen to the fermenting wort the sparger 30 can in this example be used to spray cleaning liquid into the tank after a yeast propagating operation so as to clean the tank.

In use the controller C controls the introduction of a volume of wort into the tank 12. A seed supply of yeast is either separately introduced into the tank, or introduced with the wort. The controller C then monitors the temperature of the wort/yeast mixture and the dissolved oxygen content of the mixture. The controller C controls the supply of oxygen (in this example we prefer to supply substantially pure oxygen gas) to the tank to keep the dissolved oxygen at the required level, the rate of stirring of the agitator, and the flow of the heat transfer fluid in the space 16 so as to keep the temperature at the desired level.

It will be appreciated that the vessel 10 is not air tight. The yeast grows and replicates itself in aerobic conditions with catabolite repressed activity.

The temperature in this example is maintained at 200C.

When sufficient yeast has been grown, for example after a predetermined time (eg 24 hours), or when the yeast count, PG, or ethanol level have reached a desired value (sensors to detect this may be provided) the controller operates, or is operated by a user, so as to remove the wort/yeast mixture via the pipeline 34. Clearly the heat exchanger will not be operating at this stage to sterilise the liquid since the yeast is needed alive to pitch into a brewing vessel. The yeast/wort mixture may be fed directly to a brewing vessel or it may be fed to a storage vessel first. The yeast may be filtered from the used wort before it is pitched, or it may not. The yeast may be washed before it is pitched into a brewing vessel, or it may not.

Some yeast may be left behind in the vessel 10 during the yeast extraction operation, and this yeast may seed the next propagation of yeast. Alternatively the vessel 10 may be cleaned out and new yeast used to seed propagation.

Figure 2 shows the growth of a lager yeast strain in the 800 litre propagator of Figure 1. The medium was a high gravity (OG 1060) all malt lager wort. The temperature was maintained at 200C during the propagation.

Conventional brewery propagators are effectively nothing other than scaled down fermenters. Thus, they are not designed to provide highly aerobic conditions and consist of little more than attemperated stainless steel vessels capable of hygienic operation.

In this embodiment our propagator differs in that it is provided with a heavy duty agitator, a supply of oxygen, and a sparger. These features ensure that the oxygen transfer characteristics of the vessel are highly efficient. The actual dissolved oxygen tension may be controlled, if desired, by taking the output from a dissolved oxygen meter and using this in a feedback loop to control either the rate of oxygen inflow and/or the rate of agitation. DOT sensors and this feedback control are, as previously mentioned, not essential to the invention.

We have performed trials with the pilot scale (800 litre) propagator shown in Figure 1. The results that we obtained are given in Figure 2. As shown the viable yeast count after 22 hours was ca. 200 x 106 cells/ml. This compares with traditional propagators which achieve terminal cell counts in the region of 6 50 - 100 x 106 cells/ml in 2 - 4 days.

Conditions within the propagator were aerobic at all times as shown by the positive dissolved oxygen tension. However, growth remained catabolite repressed as judged by the fact that ethanol accumulated in the spent medium. This is a potentially important distinction in that it indicates that the physiological condition of the yeast remained similar to that which is found in conventional pitching yeast. In the example shown the dissolved oxygen tension (DOT) was controlled automatically, at approximately 20% which is roughly equivalent to air saturation. The actual oxygen tension is believed not to be critical. It is commercially important to ensure that some oxygen is always present otherwise the yeast growth rate will reduce (as in fact happens in traditional propagators). From the point of view of economy of oxygen usage it is desirable to maintain a low oxygen tension. Thus we prefer to use a DOT of 30% or less, and most preferably about 20%.

With regard to scale, assuming the requirement was for a pitching rate in a 1000 brl fermenter of 15 x 106 15 yeast cells/ml: Total cells required = (15 x 106 x 1000 x 163 x 1000) = 2.445 x 1015 Assuming the yield from the propagator is 200 x 106 cells/ml; this is equivalent to: 106 13 (200 x 106 x 1000 x 163) = 3.26 x 1013/brl.

Therefore, the working volume of the propagator would need to be: 15 2.445 x 1015 = 75 barrels 13 3.26 x 10 For a working volume of 75 brl, the total volume of the propagator would need to be in the region of 100 brl (because some head space needs to be left).

Traditional propagators tend to be 50 barrels or smaller.

Claims (47)

1. A method of propagating brewing yeast comprising conducting the propagation of the yeast in a yeast containing propagation medium under substantially aerobic conditions.

2. A method according to claim 1 in which the conditions are such that the yeast propagates with catabolite repressed (or fermentative) physiology.

3. A method according to claim 1 or claim 2 in which the yeast is propagated on a feedstock that has an excess of sugar.

4. A method according to any preceding claim in which wort is used as the feedstock.

5. A method according to any preceding claim in which oxygen is available to the yeast at all times, or substantially all times.

6. A method according to any preceding claim in which oxygen is positively supplied to the feedstock containing the yeast.

7. A method according to any preceding claim in which the oxygen is provided in air.

8. A method according to any one of claims 1 to 7 in which the oxygen is provided as pure oxygen, or as a mixture that is not air.

9. A method according to any preceding claim in which the yeast is propagated in a propagating vessel.

10. A method according to any preceding claim in which oxygen is available to, or supplied to, the yeast, substantially throughout propagation.

11. A method according to any preceding claim in which propagation occurs in a propagator that is fed continuously with oxygen, or an oxygen containing gas mixture.

12. A method according to any preceding claim in which propagation occurs at relatively high temperatures.

13. A method according to any preceding claim in which propagation occurs at a temperature between 100C and 300C.

14. A method according to claim 13 in which propagation occurs at a temperature between 200C and 300C.

15. A method according to any preceding claim in which oxygen is stirred in, shaken in, agitated with, or bubbled through the yeast - containing propagation medium.

16. A method according to any preceding claim which includes mixing the yeast - containing medium in a propagator using mixing means.

17. A method according to claim 16 in which mixing of the propagation medium is provided by bubbling oxygen (or air) through the contents of the propagator.

18. A method according to claim 16 or claim 17 in which the mixing means comprises an agitator or impeller.

19. A method according to any preceding claim which further comprises controlling the temperature of the yeast - containing propagation medium in response to a temperature signal provided by a temperature sensor.

20. A method according to any preceding claim which further comprises controlling the amount of oxygen positively supplied to the yeast - containing propagation medium in response to signals representative of a characteristic of the propagation medium.

21. A method according to claim 20 in which a sensor provides signals indicative of the amount of oxygen in the propagation medium and the supply of oxygen to the medium is controlled at least in part in response to those oxygen level signals.

22. A method according to any preceding claim in which the propagation medium is mixed by mixing means at a mixing rate that is dependent upon one or more measured characteristics of the propagation medium.

23. A method according to any preceding claim in which the dissolved oxygen tension of the propagation medium is kept at between 10 and 40% during propagation.

24. A method according to claim 23 in which the dissolved oxygen tension is maintained at between 15 and 30% during propagation.

25. A method according to claim 24 in which the dissolved oxygen tension is maintained at about 20% during propagation.

26. A method of propagating brewing yeast substantially as described herein with reference to the accompanying Figures.

27. A yeast propagator vessel adapted to propagate yeast in substantially aerobic conditions.

28. A propagator according to claim 27 which has oxygen supply means.

29. A propagator according to claim 27 or claim 28 in which oxygen supply means is provided adapted in use to supply oxygen to a propagation medium in the vessel, the oxygen supply means comprising a nozzle, spray, or sparging device adapted to be immersed in the propagation medium.

30. A propagator according to any one of claim 27 to 29 in which mixing means is provided adapted in use to mix a propagation medium held in the vessel.

31. A propagator according to any one of claims 27 to 30 in which heat transfer means is provided adapted to control the temperature of a propagation medium held in the vessel.

32. A propagator according to any one of claims 27 to 31 in which an oxygen sensor is provided adapted to detect the level of oxygen present in the propagation medium.

33. A propagator according according to claim 32 in which control means is provided and in use receives signals from the oxygen sensor and controls the supply of oxygen to oxygen supply means which releases oxygen to the propagation medium.

34. A propagator according to any one of claims 27 to 33 in which a temperature sensor is provided, an oxygen sensor is provided, oxygen supply means are provided, an agitator is provided, heat transfer means are provided, and a controller is provided; the controller receiving in use a signal from the temperature sensor indicative of the temperature of the propagation medium, and a signal from the oxygen sensor indicative of the amount of dissolved oxygen in the propagation medium, and the controller operating the heat transfer means, the agitator, and the oxygen supply means so as to ensure that the propagation medium has a substantially stable temperature and oxygen content throughout a propagation operation, and so that it is substantially uniformly mixed.

35. A propagator vessel substantially as described herein with reference to Figure 1 of the accompanying drawings.

36. Yeast that has been propagated under substantially aerobic conditions in accordance with any one of claims 1 to 26, or in a propagator vessel in accordance with any one of claims 27 to 35.

37. A method of making a fermentation product comprising using yeast in accordance with claim 36.

38. A method of brewing beer comprising propagating yeast in a propagator, inoculating a fermentation feedstock (wort) provided in a fermentation vessel with yeast from the propagator, and fermenting wort in the fermentation vessel to produce beer; the method further comprising the step of producing the inoculated yeast in the propagator in conditions that are aerobic and that are arranged such that the yeast is propagated with catabolite repressed activity.

39. A method according to claim 38 which further comprises the continuous or substantially continuous supply of oxygen to the propagating yeast during the propagation process.

40. A method of reducing the process time for propagation of brewing yeast comprising propagating the yeast under aerobic conditions, and ensuring that the conditions are such that the yeast has catabolite repressed, fermentative phsyiology during propagation.

41. A method according to claim 40 which further comprises propagating the yeast in wort.

42. The use of yeast propagated in aerobic conditions with catabolite repressed activity in the inoculation of wort for brewing beer.

43. An improvement in a method of brewing beer where an initial propagation yeast supply is introduced to a first fermentation vessel and a first beer is brewed in the fermentation vessel and yeast produced during the brewing of the first brew of beer is used to pitch a second brew of beer in a fermentation vessel, and yeast grown during that brew is used to pitch a further brew of beer, and so on; the improvement comprising reducing or minimising the need to blend sub-standard beer produced by the first brew, and possibly the second brew, by the use of yeast that has been propagated in aerobic conditions in the preparation of the initial propagation yeast supply for inoculation into the first fermentation vessel.

44. A method according to claim 43 in which further comprises supplying oxygen to the propagating yeast substantially continually during its propagation.

45. A method according to claim 43 or claim 44 which further comprises making the conditions during propagation such that the yeast has catabolite repressed, or fermentative, activity during propagation.

46. A method of reducing the time to brew a batch of beer comprising using yeast that has either: (a) come from a propagator which has propagated the yeast in aerobic conditions; or (b) has a propagator source in accordance with (a) at some point in its past reproduction cycle.

47. Beer or alcoholic other beverage that has been made by a method which uses any of the inventions of claims 1 to 46.