From the HBD Archive
From: (John DeCarlo)
Subject: Rehydrating Dried Yeast
Date: 1992-04-01 14:43:32 GMT

Jack S. said:
>I had routinely rehydrated yeast with a small amount of wort for
>years but recently switched to water on the advice of "experts".
>Not one to take advice without a pinch of salt, I tried it and
>was so impressed with the vigorous foaming of EDME in water that
>I assumed that the dryed product must contain a nutrient and
>henceforth, rehydrated in water.

>In my current life as a yeast culturing microbiologist, I noted
>that when I started a culture of EDME in water, the cells in a
>water solution showed no signs of reproduction even 24 hours
>later, in spite of the successful growth on the petri medium and

OK, Jack, let me add my two cents worth. Of course water is not
a good medium for yeast growth. The only reason I know of for
rehydrating dried yeast cells in water is that the difference in
osmotic pressure on the yeast cell walls is kept down, allowing
more of the cells to rehydrate without bursting (than if you
rehydrated them in wort). This process may take about 5 or 10
minutes. Then you immediately put them in a growth medium, such
as wort.

It is sort of like eating some food and taking some aspirin and
vitamins before going to the bachelor party. <grin>

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