Author Topic: Rehydrating Dry Yeast  (Read 6274 times)

Offline Pi

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Re: Rehydrating Dry Yeast
« Reply #30 on: February 14, 2013, 09:20:30 AM »
when rehydrating dry yeast, using cooled boiled water, the fact that the O2 has been cooked off any concern?
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Offline denny

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Re: Rehydrating Dry Yeast
« Reply #31 on: February 14, 2013, 09:36:53 AM »
when rehydrating dry yeast, using cooled boiled water, the fact that the O2 has been cooked off any concern?

I don't think so.  You need O2 for cell growth, and when you rehydrate dry yeast you're not going for cell growth.
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Offline tom

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Re: Rehydrating Dry Yeast
« Reply #32 on: February 14, 2013, 10:01:18 AM »
And it is all set up with lots of sterols.  Dry yeast may need less O2 than liquid.
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Offline CASK1

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Re: Rehydrating Dry Yeast
« Reply #33 on: February 14, 2013, 08:37:19 PM »
Here's a nice article on the topic from Northern Brewer:

http://www.northernbrewer.com/connect/2010/06/the-importance-of-being-hydrated/

Offline bazowie

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Re: Rehydrating Dry Yeast
« Reply #34 on: February 18, 2013, 04:03:19 PM »
The yeast book I bought from AHA recommends to rehydrate at 105 deg, wait, stir, cool to pitch temp, and pitch.
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Offline dimik

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Re: Rehydrating Dry Yeast
« Reply #35 on: March 13, 2013, 07:43:10 PM »
Actually I don't think you need oxygen for rehydration for two reasons:
1 - Dry yeast should have whatever they need to get started in the preservative.
2 - Oxygen is actually a very toxic thing. Just because we evolved to use it doesn't mean that it's good for life all the time. So I'd imagine high oxygen concentration in water/wort would result in even more cell death while their membranes are still fragile and not rebuilt. Afterwards, pitching into a well oxygenated wort would be good because it would help in growing and forming stronger membranes, which would prolong and improve their activity and viability.

Here is a little experiment I did to follow up on the original topic
http://bkyeast.wordpress.com/2013/03/13/more-on-yeast-rehydration/
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Offline davidgzach

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Re: Rehydrating Dry Yeast
« Reply #36 on: March 14, 2013, 04:28:36 AM »
when rehydrating dry yeast, using cooled boiled water, the fact that the O2 has been cooked off any concern?

I don't think so.  You need O2 for cell growth, and when you rehydrate dry yeast you're not going for cell growth.

+1.  Or in it's absence for cell growth, sterols and fatty acids.  Hence the olive oil experiment.
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