GB2138021A

GB2138021A - Yeast fermentation

Info

Publication number: GB2138021A
Application number: GB08308566A
Authority: GB
Inventors: Stanley Kimber
Original assignee: POLYTHENE DRUMS
Current assignee: POLYTHENE DRUMS
Priority date: 1983-03-29
Filing date: 1983-03-29
Publication date: 1984-10-17
Also published as: GB2138021B; GB8308566D0

Abstract

The present invention provides an improvement in fermentation methods and fermentation vessels wherein the fermentation liquid is separated from the yeast residuum without substantially disturbing the liquid in the fermentation vessel. This is achieved by providing a fermenter (1) with inclined walls (3) terminating in a lower outlet (4) valved at (6) by which the lees (12) may be regularly removed by operation of the valve (6) during the course of fermentation, The fermenter may be a closed vessel fermenter provided with an opening closed by an air-lock, the air-lock passage may be provided with an obturating valve, thereby to increase the carbon dioxide pressure to super atmospheric pressure at any desired point during the fermentation. <IMAGE>

Description

SPECIFICATION Fermenting vessel and method The present invention relates to a method for controlled fermentation, particularly of alco holic beverages, and to a suitable fermenta tion vessel for use therewith.

Fermentation methods and apparatus, parti cularly on the small scale, are well known. In one such method for the production of wines and beers, an open topped jar is provided with a closure means comprising an air-trap.

The jar is filled with a wort or must and fermented with a suitable yeast until the fer mented liquid has cleared and the yeast resi duum has fallen to the bottom of the jar, The liquid is then syphoned out of the jar into a second similar jar and the process repeated until the end of fermentation.

Alternatively, such a jar may be provided on its vertical side wall at a distance of 2 or 3cm.

ffrom the bottom of the jar with a tap which can draw off the liquid while leaving the yeast residuum (lees) undisturbed.

In order to obtain an acceptable alcoholic beverage it is often necessary to "rack" the fermenting liquid at least twice in order to remove decomposing yeast residuum and to prevent its secondary reaction with the fermenting liquid. The secondary reaction tends to cause poor flavours in the eventual product.

The use of a syphoning tube to syphon the liquid from the fermenting jar is a messy and time-consuming procedure and requires some skill to avoid portions of the yeast residuum being transferred to the new vessel. In common with the arrangement wherein a tap is used for drawing the liquid from above the yeast residuum, the transfer of the partially or fully fermented liquid in fact must result in partial oxygenation of the fluid which is microbiologically undesirable since it encourages growth of microbiological organisms other than yeast at a time when the yeast population is being purposely diminished.

For the above reasons, the racking of alcoholic beverages is kept to a minimum, not only because it is time consuming but also because of possible infections of the partially or fully fermented beverage.

The present invention seeks to overcome these problems by providing in the first aspect a fermentation method which comprises adding yeast to a suitable fermentable substrate in a fermentation vessel, causing or allowing fermentation to proceed toward completion, and separating the fermented liquid from yeast residuum, characterised in that the yeast residuum is removed from the fermenting vessel while the liquid remains substantially undisturbed therein. The yeast residuum may be removed at frequent intervals during the course of the fermentation, thereby improving taste by avoiding secondary reactions between the yeast decomposition products and the substrate, and avoiding oxygenation.

The suitable fermentable substrate may be a wort or must, or apple extract, or indeed any extract of a suitable plant, for example those used in "country wines" and derive from blackberries, wortleberries etc.

The yeast is most preferably removed by providing the fermenting vessel with inwardly and downwardly inclined wall or walls having an angle to the vertical such that the yeast residuum cannot adhere thereto in any substantial amount, and therefore falls to an apex formed adjacent a valved bottom outlet. The inwardly and downwardly inclined wall may be a frusto-cone. Accordingly, opening the valved bottom outlet will allow the yeast residuum to flow from the fermenter without without substantially disturbing the fermenting or fermented liquid therein.

A suitable angle for the inclined walls may be 25-40' from the vertical. It will be appreciated that the bottom outlet allows the residuum and the clear fermented liquid to flow from the same valve in sequence, and accordingly, the processes of yeast residuum separation by racking and where desired, final dispense can be achieved through the same valve with the minimum of effort.

It is most preferred that the fermenter is a closed fermenter, and in which case it is usual to provide as in the prior arts, an upper outlet incorporating an air-lock in standard form.

In the present invention, the air-lock may also be provided with a obturating valve which may be used during fermentation to raise the internal pressure of the fermenter by carbondioxide evolution. This has the effect, when correctly used, in assisting the yeast residuum's settlement, and in its expulsion from the bottom outlet should the yeast residuum become compacted, (as can happen when racking is delayed for a good period).

This arrangement has a further advantage in that the CO2 evolved can be used initially to purge oxygen from the closed vessel, and subsequently with the obturating valve closed, can be utilized as "top pressure", ie: as an inert pressurising gas which prevents oxygenation of the fermented liquid. In such an arrangement it is usual to provide a separate safety valve which prevents closed vessels from being subjected to too great a pressure.

Fermenters of the present invention may be made of a clear or semi-transparent plastics material of food-grade quality, or out of glass, and may be wall mounted or free standing as desired.

Thus, in accordance with the second embodiment of the present invention, there is provided a fermenting vessel, comprising inwardly and downwardly inclined wall or walls, having an angle to the vertical such that yeast residuum cannot readily adhere thereto, said wall terminating in an apex provided with a valved outlet, whereby fermented products and yeast re-siduum can be removed sequentially.

The wall may include a frusto-cone which terminates at said apex. The vessel may be a closed fermenter including means for retaining carbon dioxide evolved during fermentation therein The invention will now be described, by way of illustration only, with reference to the accompanying drawing which shows in vertical section a closed vessel fermenter according to the invention.

A fermenting vessel (1) having a generally circular transverse cross section is provided in vertical section with an upper portion (2) generally in the form of a cylinder terminating at its lower edge in a frusto-cone (3) having its apex end downwardly directed. The apex end of the frustocone (3) terminates in outlet (4) disposed about the vertical axis of the vessel. The outlet (4) is closed by a stopper (5) provided axially with a tube valved at (6) whereby the yeast residuum (lees)(1 2) can pass through the tube via the valve (6) to the exterior.

The angle formed between the vertical and the inclined walls of the frusto-cone (3) is,in this instance, between 20 and 30 . However, angles of 45 from the vertical and in some cases even greater can be made to work, while angles more acute than 25 tend to restrict the size of the fermenting vessel by making it excessively tall.

The upper end of the fermenting vessel is conventionally provided with a top stopper (8) bored to receive an air-lock (9); said stopper(8) being adapted for close co-operation with a bore disposed in an upper wall (7) of the closed fermenter.

In use, the stopper (8) with the air-lock (9) is removed from the upper wall (7) and a wort or must is introduced via the aperture therein so as to fill about 80 or 85 of the volume of the closed fermenter. Suitable capacities for small scale operation are 1 and 5 gallons, but of course, much larger fermenters can be used if desired. A suitable yeast starter mixture is introduced, the wort or must stirred or otherwise admixed, the whole raised to a fermentation temperature and closed with the stopper (8). The fermentation will then proceed at a rate dependent on temperature until the initial fermentation has been substantially completed. During this period, the space above the fermentation liquid is purged of air by evolving carbon dioxide; the gases being forced through the air-lock to the exterior.At convenient moments, for example every day the drain tap (6) may be opened to release the lees and promptly closed again to retain the fermenting liquid. At the end of a period, for example, of three weeks, the liquid will have completely cleared without the necessity for separate racking operations. If the air-lock is maintained in situ the fermented liquid can be retained without separate racking or bottling operations until use is desired. At this point the air-lock assembly must be replaced, or at least removed during drawing off of the beverage for use.

Storage in this condition is possible because the carbon dioxide gas evolved from the fermentation seals the liquid against oxygenation, and hence prevents deterioration of the product. Should any yeast residuum occur during storage of the beverage it is, of course, readily possible to merely open the valve (6) and discard the small portion of residuum before utilizing the cleared liquid.

In an alternative, the air-lock (9) may be replaced by a safety valve which allows carbon dioxide to escape to the exterior only after exceeding a predetermined pressure within the vessel. This has the effect of partial carbonation of the contents which can itself be desirable while assisting in prevention of oxygenation by maintaining the contents of the vessel at super atmospheric pressures.

It will be appreciated that by use of the fermenter and methods as described, not only is racking avoided, but also the product can be fermented, stored and dispensed from the same vessel without the necessity of purchasing further vessels for fermentation and storage. Further, because the lees are regularly removed, undesirable taste defects caused by secondary action of yeast residuum with the fermenting liquid are avoided. Self-carbonation . can also be achieved in the same vessel to any desired degree without the inconvenience of racking operations.

The present device is particularly useful for small scale fermentations, but the advantages of the fermentation method may be achieved with fermenters of any scale.

Claims

1. A fermentation method which comprises adding yeast to a suitable fermentable substrate in a fermentation vessel, causing or allowing fermentation to proceed to completion, and separating the fermented liquid from the yeast residuum, characterised in that the yeast residuum is removed from the fermenting vessel while the liquid remains substantially undisturbed therein.

2. A method as claimed in claim 1 wherein the yeast residuum is removed at frequent intervals during the course of fermentation.

3. A method according to either of claims 1 or 2 wherein the fermentable substrate is a wort, must or apple extract.

4. A method according to any preceding claim wherein the yeast residuum is removed by providing the fermentation vessel with an inwardly convergent wall or walls, terminating in a lower apex outlet, said wall or walls having an angle to the axis of the vessel such that participating yeast residuum cam ot substantially adhere to the wall or walls.

5. A method according to claim 4 wherein the vessel is part cylindrical and the convergent wall is a frusto-cone.

6. A method according to either of claims 4 or 5 wherein the angle of the convergent wall or walls to the axis of the vessel is 25 to 40 .

7. A method according to any preceding claim wherein the vessel is adapted for closed fermentation, and is provided in addition to an air-lock with an obturating valve, thereby to retain carbon dioxide within the vessel at super atmospheric pressure.

8. A method substantially as hereinbefore set forth with reference to, and/or as illustrated in the accompanying drawing.

9. A fermenting vessel for alcoholic beverages comprising a convergent wall or walls; said convergent walls having an angle to the axis of the vessel such that yeast residuum does not substantially adhere thereto.

10. A vessel according to claim 9 wherein said angle is up to 45 from the axis of the vessel.

11. A vessel according to claim 9 wherein said angle is 25 to 40 from the axis of the vessel.

1 2. A vessel according to any of claims 9 to 11, wherein the vessel is formed of an upper cylindrical portion and a lower frustoconical portion, said lower portion terminating at its lower extremity in a valved outlet.

1 3. A vessel according to any one of claims 9 to 1 2 wherein the vessel is adapted for closed fermentation and includes second valve means adapted to obturate a passage to a closed fermentation air-lock, thereby in use to provide means for raising the carbon-dioxide evolved during fermentation to super atmospheric pressures.

1 4. A vessel substantially as hereinbefore set forth with reference to and/or as illustrated in the accompanying drawings.