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Author Topic: Yeast harvest  (Read 4854 times)

Offline hopfenundmalz

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Re: Yeast harvest
« Reply #30 on: December 11, 2015, 06:19:24 am »

Why did you refrigerate so soon?  I typically leave my starters on the stir plate until they ferment out.


I was hoping to realize some of the supposed benefits of pitching the starter at high krausen without pitching the entire volume of the starter.

I've been experimenting with pitching an entire 1 liter starter at high krausen into ales, but I like to pitch more cells for lagers and couldn't bring myself to pitch a full 2 liters.

For more info, search this forum for the term "ergosterol" by user "s. cerevisiae."

I'm getting ready to do a series of lagers (hope it cools off here - did I say that?). My thinking is that I will pitch the full shaken not stirred starter. The recipe will be bumped up in OG and hops to compensate for the dilution.
Jeff Rankert
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Re: Yeast harvest
« Reply #31 on: December 13, 2015, 11:07:25 am »
Why did you refrigerate so soon?  I typically leave my starters on the stir plate until they ferment out.

I have posted this information many times, but allowing a starter to ferment out before pitching it is not a good practice because it places the cells in a state known as quiescence.  Yeast cell undergo survival-related morphological changes in preparation for quiescence that have be reversed after being pitched.  The need to reverse these changes coupled with less complete ergosterol and unsaturated fatty acid reserves results in increased lag time and O2 demand. 

High krausen marks the end of the exponential phase.  All reproduction past this point is for replacement only .   As the mother cells share the ergosterol and UFA reserves that were synthesized during the lag phase with their daughter cells and their daughters share their ergosterol and UFA reserves with their daughters and so on, allowing a starter to proceed past high krausen wastes ergosterol and UFAs.  Pitching at high krausen preserves these compounds and shortens the lag phase.  It also reduces the O2 demand upon pitching.