General Category > Yeast and Fermentation

Don't make yeast starters from dry yeast? WTF?

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dimik:
I didn't see anyone bring up the main issue (in my opinion). Which is if you make starter with dry yeast, you'll kill about 50-60% of them right off the bat. It is better to rehydrate dry yeast in warm water (35-40*C - 95-104*F) for 15-20 min and then gradually cool and add to wort or starter. This has to do with the fact that dried cells have damaged membranes and need time to rebuild them, "patch the holes", resume membrane transport control, etc. Otherwise they have no control as to what goes in or out of cells. That happens fairly quickly, but still takes a few minutes. Temperature also plays a role. Rehydrating in cool water ~60*F will usually kill about a half of them. Now if you put dry yeast into a starter, the relatively high sugar concentration (yes, even 1.030 is high relative to dry yeast) and hops (if any) will destroy a lot of cells so essentially you'll be raising the starter to get back up to the number of cells that was there to begin with.
Another thing is that dry yeast packets contain approx 200 billion cells, and if you put directly into wort and kill half of them in doing so, there will still be enough cells left to normally ferment your average beer.

dimik:

--- Quote from: mtnrockhopper on January 28, 2013, 07:53:03 AM ---
--- Quote from: weithman5 on January 28, 2013, 07:47:31 AM ---when you sprinkle it into your wort, you really aren't re-hydrating in alcohol though

--- End quote ---
No, but from what I hear (I haven't asked the yeast personally) is that their cell walls are inactive and some will die from the rush of sugars entering their cells. Once rehydrated in water they can fight the osmotic pressure.

--- End quote ---

Hehe. You posted this while I was writing the reply above. :)

Jimmy K:

--- Quote from: dimik on January 28, 2013, 07:55:07 AM ---
--- Quote from: mtnrockhopper on January 28, 2013, 07:53:03 AM ---
--- Quote from: weithman5 on January 28, 2013, 07:47:31 AM ---when you sprinkle it into your wort, you really aren't re-hydrating in alcohol though

--- End quote ---
No, but from what I hear (I haven't asked the yeast personally) is that their cell walls are inactive and some will die from the rush of sugars entering their cells. Once rehydrated in water they can fight the osmotic pressure.

--- End quote ---

Hehe. You posted this while I was writing the reply above. :)

--- End quote ---
I'm a ninja.

suprchunk:

--- Quote from: weithman5 on January 28, 2013, 07:47:31 AM ---when you sprinkle it into your wort, you really aren't re-hydrating in alcohol though

--- End quote ---
I think Kai was responding to the person saying that trying to pitch on a stuck fermentation never worked for him/her. Actually, I don't think it, I know. Since he quoted him and all.

industrialpunk:
Here a Danstar yeast expert explains why you rehydrate but DO NOT make a starter:
http://koehlerbeer.com/2008/06/07/rehydrating-dry-yeast-with-dr-clayton-cone/

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