Method of Storing Yeast

General Considerations

• 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

• 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.
• 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.

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