Yeast recovery and preservation

Yeast is commonly known as the soul of beer production. It achieves different styles and flavors of beer, and directly affects the normal progress of fermentation production and the quality of beer. Therefore, the quality, performance and living environment of yeast itself are the decisive factors for beer flavor. , so yeast management is a very important task.

Today I would like to share with you the content of yeast recovery and preservation commonly used in beer production.

In order to ensure that the activity of yeast is not affected by the outside world, or to minimize harmful effects, the principle of "short-term storage, low-temperature storage, single-strain storage, and timely access" should be followed for yeast recovery and storage.

Yeast Recovery Time:

When the main fermentation is completed, a large amount of yeast settles at the bottom of the fermenter cone. At this time, the yeast basically loses the ability to re-ferment and reduce the diacetyl of the original fermentation liquid. At this time, it should be recovered in time. If the recovery time is too early, the earliest dead yeast or senescent yeast, as well as the residues such as cold coagulation and hops, will be recovered; if the recovery time is too late, the yeast that settles at the bottom of the fermenter cone will accumulate for a long time. High temperature (5°C and above), high pressure, alcohol influence will accelerate aging, degeneration, death and autolysis, so the quality of the recovered yeast is poor.

Yeast recovery quality requirements:

1. The recovered yeast mud must be white, viscous, free of sour taste and peculiar smell; the cells should be uniform in size, neat in shape, thick in cell wall, and uniform in cytoplasm without abnormality when examined under a microscope.

2. The mortality rate of recycled yeast mud should be less than 3%, and should not exceed 10% at most.

3. In order to ensure the strong and good activity of the yeast and reduce the chance of being contaminated by miscellaneous bacteria, the generation of the recovered yeast should be controlled within 3 generations.

4. When recovering yeast, according to the law of yeast sedimentation, follow the principle of "pinch the head and remove the tail, and take the middle".

Yeast recovery method:

1. Manual recycling

The yeast that settles at the bottom of the cone of the fermenter is roughly divided into three layers. The bottom layer of yeast discharged first is weak cells and dead cells, mixed with a large amount of sediment impurities, which can be used as feed or discarded; the middle layer is new cells with strong fermentative power, accounting for about 75%, which should be taken out separately and reserved for future use. ; The upper layer is multi-light cells, mixed with residues such as protein and hops. After separation, it can be used as feed or discarded.

2. Centrifuge recycling

Using the different relative densities of yeast and fermentation liquid, centrifuge is used to separate wine liquid and yeast. This method is easy to operate, but the disadvantage is that the centrifuge equipment is not easy to sterilize and the centrifugation process is easy to absorb contact with oxygen, resulting in an increase in yeast mortality.

Yeast preservation

For the yeast recovered in time, if there is no storage condition, it should be inoculated into the cold wort as soon as possible; if there is a storage condition, it should be treated: that is, it should be fully, quickly and evenly cooled to the temperature where its metabolic activity is slow to the lowest limit ( Usually controlled at 2~4℃) storage. Recovered yeast cooling method: plate heat exchanger or yeast storage tank jacket cooling; plate heat exchanger cooling can make the yeast cool fully, quickly and evenly, and the yeast cools gently; jacket cooling will cause uneven cooling; yeast storage time after cooling Shorter is better.

Yeast recovery

The total amount of yeast recovered is related to the original wort concentration, wort oxygen content and yeast proliferation; it is not proportional to the yeast inoculum. The higher the concentration of the original wort, the more assimilable nitrogen it contains, which is more conducive to the proliferation of yeast; the higher the oxygen content, the stronger the proliferation of yeast, and the greater the recovery. The higher the yeast inoculation amount, the less the proliferation of newborn yeast under the limited wort nutrition condition, and the relative reduction of the yeast recovery rate.

Yeast Recycling Considerations

1. In the process of recycling and storage, sanitation must be done well, and it is strictly forbidden to contaminate miscellaneous bacteria.

2. Try to avoid contact with oxygen, because oxygen contact will accelerate the yeast's aerobic respiration, thereby accelerating the consumption of the yeast's own glycogen reserves