Yeast from fermentations should be carefully selected and stored so as to maintain a continual supply of pitching yeast
Temperature and time of storage should be controlled to produce pitching yeast of consistent quality (viability, homogeneity and composition).
Requirements for pitching yeast may vary according to brewery operations, production targets and whether pitching yeast is supplied to other breweries.
Range of Values
Ideally yeast is reused within 48 – 72 hr Some yeasts need to be stored for a minimum of 24 hr. Storage time should not exceed 7 days.
Storage temperature is 1° – 4°C (34° – 39° F) It should be noted that the temperature of the yeast room and that of the yeast itself can differ markedly particularly with compacted pressed yeast or concentrated slurries.
Yeast is stored as pressed yeast (20 – 27% dry matter) or as a slurry (ca. 10% dry matter)
Operational Protocols
The yeast press or receiving vessel should be cooled to 1°C (34° F) to maintain yeast at low temperature and/or reduce temperature as quickly as possible.
Handling plant must be adequately cleaned and sterilised. Where possible siting of yeast presses should be carefully chosen to minimise pick-up of air-borne contaminants.
There are several methods of operation depending on the type and size of fermenters and the method of cropping used. Some examples are:
Yeast from the fermenler is passed via a filler press to a mixing vessel, reslurried with water and stored at 2° C (36° F) with stirring
Yeast from the filter press is stored as filter ‘cake’ on trays in a cold room at 1° – 4° C (34° – 39° F).
Yeast from the fermenter is stored as yeast slurry under beer at 2°C (36° F).
With cylindroconical vessels yeast is often transferred directly from one vessel to another.
Measurement Protocols
The temperature of the yeast during storage should be checked.
Viability, composition, percentage dry matter and contamination of yeasts are measured as described in The State of Yeast at Pitching