Cropping your yeast is a traditional and well-established approach to maintaining the character of your beer – and reducing production costs. Fermentation growth produces twice as much yeast per brew so giving a good stock for future use if hygienically collected.
However, ensuring consistency of yeast cultures is critical for routine production and to avoid an incomplete fermentation. Repitching your yeast saves the cost of regular purchase but genetic drift can occur with repeated stressing causing changes in viability, flocculation and flavour (Kalyu review 2019). This is accelerated if oxygenation is insufficient before pitching and can show changes within 3 to 5 generations. However, effects appear to be strain dependent and can differ with different worts being particularly affected by high gravity brewing. To check this Brewlab can test your strain for the effects of repatching using small scale laboratory cultures and provide advice on optimal handling for long term management.
Here is an example showing the effects of common stresses, high gravity 1080 wort, acid washing and oxygen radicals on the growth of eight different yeasts. Each pair of curves show the kinetics of growth (delay, rate or growth and productivity) under each condition. Different yeast show variable responses to each stress allowing specific advice in handling to be provided.