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We boil DME and water to make a solution with an OG of 1.040, pitch the yeast and place it on a stir plate for a couple of days to make our yeast starters. After this, it is commonly suggested to place the flask in the refrigerator for 12 or more hours to flocculate the yeast, thereby allowing us to pour off the DME wort so our real wort does not get cut with the yeast-starter/DME wort.

Why does this not inactivate or cold crash the yeast?

My fridge measures roughly 30F.

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marked as duplicate by Graham, mdma Jul 11 '13 at 21:42

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up vote 4 down vote accepted

It does cold crash them, reducing activity to force them to flocculate and sediment out of solution. It does passivate them, generally shutting down their metabolism. It does not inactivate or destroy them, however; the yeast are still alive, just dormant. Bring them back up to pitching temperature and introduce them to fresh wort, and they will reproduce and ferment as appropriate.

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