The Do’s and Don’ts of Yeast Handling
By Moritz Kallmeyer
Chief Brewer Drayman’s Craftbrewery, Silverton, Pretoria, November 2003
The aim of this article is to discuss improved methods of yeast handling in a brewery to ensure good yeast health and optimum fermentation performance.
The reality in most craftbreweries is that brewers don’t handle their yeast correctly ultimately impacting negatively on beer flavour. Conventional methods by old timers rarely involved much more than collecting yeast from a previous batch and unceremoniously dumping it into a new batch.
- The first step in ensuring that the next batch of yeast collected will be of good health is: daily trub removal from the fermentation vessel (FV).
- As soon as the yeast has dropped out of suspension (before chillback) The yeast must be warm cropped. Early warm cropping has significant benefits on yeast vitality.
- Yeast to be stored must be chilled down immediately to 0-2ºC. The thin early crop contains enough beer that will form a hydrative layer on top of the yeast in the storage vessel. No CO² pressure build up is allowed – due to the risk of CO² poisoning.
- Collected yeast should not be cold stored (before repitching) for longer than three days(optimum) or seven days (worst case scenario)
- Removing a batch of yeast from cold storage , critical inspection of the yeast, and timely acid washing of the yeast are some of the first routines on a brewing day. Principals of acid washing includes beer layer removal, dilution with sterile acidified water, pH lowering to 2.1-2.2; straining to remove protein trub; sedimentation to remove dead cells and regular uniform mixing.
- After a period of settling (+/- 3 hours) the excess acid water forming a layer on top of the yeast is removed and the yeast roused with fresh sterile wort from the kettle (5% of yeast volume) and sterile cold water.
- After rousing, the yeast is allowed to gradually atemperate to close to pitching temperature to avoid any temperature shock.
- One of the guiding principles in yeast handling prior to pitching is the adequate mixing of yeast until a uniform, decarbonated suspension has developed.
The key words in yeast handling are keep it cold (KIC), keep it short (KIS), keep it simple (KIS)