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Date: Thu, 7 Oct 93 16:10:28 -0400
From: (Joyce Miller)
Subject: Re: Yeast + Nutrient = Death?

>Hi. I made a small mead this weekend, but something funny happened to
>the yeast. I hydrated it in a glass of warm water, with a half
>teaspoon of "yeast nutrient" (no specifics on the label) in the glass.
>The yeast wound up sitting there in the kitchen for at least an hour,
>because there were complications in chilling the must. I pitched it
>and waited for something to happen for about 36 hours. Since there was
>no sign of activity, I just dumped another packet of yeast straight
>into the fermentor. The mead took off a few hours later.
>So I’m wondering, did the yeast nutrient somehow kill the yeast? The
>phrase "osmotic pressure" comes back to me from high school biology. . . .

No, I’ll bet the water killed the yeast. And osmotic shock was probably
the cause. Most yeast packets I’ve seen instruct you to hydrate the yeast
in water briefly (like a few minutes), then add the starter solution
(wort/must). When a single-celled organism is placed in pure water, the
water rushes through the cell wall & membrane in an effort to equalize the
osmotic pressure — basically, to dilute out the relatively high
concentration of "stuff" on the other side (inside the cell). It’s one of
those laws of nature & chemistry. Now, most cell membranes contain "pumps"
to keep that water out, but they can’t withstand pure water for long. The
yeast nutrient probably allowed them to die less slowly (by somewhat
equalizing the pressure by being dissolved "stuff" outside the cell), but
couldn’t save them. All of your single-celled friends probably exploded.

I just rehydrate mine in cooled wort.

– — Joyce

End of Mead Lover’s Digest