Yeast storage

If a cropped yeast culture is not stored properly, cell consistency will suffer, and it will adversely affect fermentation and beer quality. After cropping, the yeast is stored in a room that is conveniently sanitized and contains a plentiful supply of sterile water and a separate filtered air supply with positive pressure to prevent the entry of contaminants at a temperature of 0°C. Alternatively, insulated tanks in a dehumidified room can be used. In addition, off the shelf yeast storage facilities are available at various working capacities. 

The number of times that a yeast crop (generations or cycles) is used for wort fermentations is usually standard practice in a particular brewery. Typically today, a lager yeast culture is currently used 6-10 times before reverting to a fresh culture of the same strain 

These days, some breweries have adopted a larger yeast reuse specification as few as four to six cycles. 

The reason why mnltiple yeast generations can have a negative effect on a culture s fermentation performance is nnclear. However, multiple generations will result in reduced levels of intracellular glycogen and an increase in trehalose, indicating additional stress conditions as the cycles progress (Table 2.3) (Boulton Qnain, 2001). 

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A convenient source of trehalase is bakers yeast. It is an a-n-glu-cosidase distinguishable from maltase by the damage suffered by the maltase on yeast storage. a,a-Trehalose added to bakers yeast is fermented (in aqueous suspension), but the a,a-trehalose stored within the yeast remains unaffected. Evidently, there is a spatial separation between yeast trehalase and its stored trehalose. The enzyme may be at the cell... 

Figure 2.5 Effect of yeast storage temperature on intracellular glycogen concentration.

The dry yeasts have excellent storage stabiUty, up to a year or more if packaged under an inert atmosphere (N2, CO2, or vacuum). First introduced into the United States and then AustraUa, they are now being introduced into European winemaking as well. A number of strains of S. cerevisiae S. bayanus and S. fermentati are available. 

Self-initiated reaetions, e.g. pymvie aeid on storage ean beeome oxidized by air (or airborne yeasts) to form suffieient gaseous earbon dioxide to overpressurize the eontainer ... 

Brewing Austenitic steels are used in fermentation vessels, storage tanks and attemperators, in yeast processing, and for transport tanks and barrels. 

The production of heers and ciders requires the fermentation of sugary fluids hy the action of yeasts, and the cooling, filtration, clarification and storage of the resulting alcohol-water mixture. 

Many medicines contain a wide variety of ingredients, often in quite complex physicochemical states, included to create formulations which are efficacious, stable and sufficiently elegant to be acceptable to patients. Should microbial contaminants survive manufacture, or enter during storage or use they are likely to meet conditions which are often conducive to survival and even replication of an appreciable assortment of non-fastidious bacteria, ftingi and yeasts, and microbial spoilage may ensue unless steps are taken to control it. Microbial spoilage may include ... 

In yeasts and other fungi, the vacuole is an important organelle sharing some properties with the mammalian lysosome (an acidic compartment containing a variety of hydrolytic enzymes) and with the plant cell vacuole (responsible for metabolite storage and for cytosolic ion and pH homeostasis) [18,19]. 

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