I have read repeatedly that yeast will mutate after several reuses in the homebrew environment. If the yeast mutate at this high of a rate, how do breweries maintain consistent yeast characteristics, and how are pure cultures maintained without mutations?
If yeast mutate at such a rapid rate, how are yeast characteristics maintained over the period of many years as we have seen. It seems to me that the culprit is not mutation, but more likely contamination.
- Sven Pfitt
Mutation does occur. Sometimes naturally and sometimes from abuse such as excessive or abusive acid wash. There is no real handle on how much of a problem it is. Sometimes it takes sophisticated equipment to detect the mutation plus a DNA fingerprint on the original strain. Sometimes mutation occurs on a portion of the gene that does not effect the beer making ability of the yeast and go undetected because it does not effect the beer.
The big commercial breweries minimize the mutation problem by repitching only 3 to 5 times (this minimizes infection problems also). They also draw from a master source or culture on an infrequent bases (yearly?) and prepare enough slants or tubes from that source to last an extended production period. They frequently DNA fingerprint inoculums to be certain that no mutation has occurred. You are right. Infection is much more of a problem.
Dr. Clayton Cone