QUESTION:
Cold Pitching, Why does it seem to work? In certain brewing forums there has been much discussion related to cold pitching yeast into ale worts. Basically, about a pint of yeast is harvested from the primary of a brew batch and stored in a sealed container at refrigerator temperatures (about 45F). At some later time (perhaps as long as 1-2 months), that yeast is pitched directly from the refrigerated container into a new batch of sweet wort @ 70-75F. Based on my experience (and observations) this method works quite well, and appears to reduce lag times (from 1.5 to 4 hours). Can you help us understand why the cold pitching process works? Or have we just been lucky?
-Mike Zapolski
RESPONSE:
I have not seen any studies done using this protocol. If I had to take a guess it would be centered around the Trehalose content in the yeast cell. Trehalose seems to be an all around stress related factor. Almost immediately upon the cold storage of the yeast, trehalose begins to build up to help the yeast to adapt to its new environment. Upon pitching this stress factor assists the yeast to adapt to its new environment; warmer temperature and higher osmotic pressure. If the pitching yeast is allowed to warm up for any appreciable time before pitching the carbohydrate reserve, trehalose being one of them will be quickly used up as an energy source. The yeast would then take a longer time adapting to its new environment in the wort thus increasing the lag phase.
Something similar happens when using Active Dry Yeast. The factory builds into each yeast cell an abundance of the stress factor; trehalose. Our recommendations is to rehydrate the yeast in warm water and pitch into the wort (or must) within 30 minutes, because the yeast will begin to metabolize its carbohydrate reserve including trehalose immediately upon reactivation and weaken the yeast if it is not in the presence of a new supply of energy. It will have also used up the stress factor that would have assisted it in adapting to the new osmotic environment. I am sure that there is more to the explanation than I have given.
Dr. Clayton Cone