Like everyone else, I really do appreciate your help and understanding and I hope my questions won't be too silly for you.

We're told yeast will adapt to the medium, at least for scale. But does it also adapt to other characteristics of the medium? If so, would it be possible to lead a yeast strain to adopt different characteristics for further batches?

If the adaptation is simply based on selective pressure and random mutations, one would imagine there's little that can be done.

-Alexandre Enkerli

RESPONSE:

I am not sure that I understand your comment 'at least for scale'. Yeast do have the ability to adapt, with limitations, to stresses in the media such as osmotic pressure, alcohol levels, upper temperature range.

This adaptation is usually done by an increase in the production trehalose. The adaption is usually temporary for a specific stress. Yeast adapt to nitrogen deficiency by stopping fermentation (stuck fermentation). Yeast that goes through several nitrogen deficiency pitchings will end up with its cell wall surface hydrophobicity altered, adversely effecting the flocculating properties.

Sometimes an adaption to a stress can become permanent after many, many transfers, sometimes hundreds of transfers. These adaptions do not always remain stable, they may resort back to the original after several generations. It is asking a lot to get a yeast to change its genetic make up in a single exposure to a wort, must or mash. It has taken eons of time for that particular strain to develope its genetic profile. Man can step in and make a change by breeding through mating and fusion.

Random mutation can be speeded up by exposing the yeast to radiation or certain chemicals then screen to look for positive improvements. Genetic engineering is the straight forward way of tailoring a new yeast for your desired purpose, however, it is generally not accepted by the public.

All is not lost. There are still untold thousands of yeast strains out in nature awaiting to be isolated and discovered. Each with particular properities that the beer and wine maker are looking for.

Dr. Clayton Cone