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Old 01-01-2013, 12:01 AM   #1
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Default Re-hydrating yeast kills?

I have read mixed reviews about re-hydrating dry yeast and pitching yeast in cool temps. So, if pitching yeast in high temperature wort kills the yeast then how does re-hydrating yeast not kill, considering the water temp for hydrating yeast is 90-110 degrees? Sorry for the noob question

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Old 01-01-2013, 12:12 AM   #2
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Wort in that temp range doesn't kill yeast, it does cause the yeast to produce off flavors during fermentation.
I rehydrate at the lower end of that, about 90 deg.
I always rehydrate when using dry yeast.

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Old 01-01-2013, 12:14 AM   #3
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It doesn't necesarily kill the yeast; if you pitch that high the beer won't have time to cool enough before fermentation begins and off flavors will be produced. That being said, this situation may be favorable for some Belgian yeasts.


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Old 01-01-2013, 12:15 AM   #4
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Originally Posted by menerdari View Post
Wort in that temp range doesn't kill yeast, it does cause the yeast to produce off flavors during fermentation.
I rehydrate at the lower end of that, about 90 deg.
I always rehydrate when using dry yeast.
I plan on doing that with my next batch, just wanted to make sure the high temps won't harm the yeast. I pitched dry yeast in my first batch and it was fermenting like crazy in under 8 hours.
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Old 01-01-2013, 12:18 AM   #5
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Rehydrating dry yeast is different than pitching it into HOT wort/must.

From the Lalvin Labs web site (applies to their strains, other strains can have different temperatures to rehydrate at)...

REHYDRATION
Dissolve the dry yeast in 50 mL (2 oz) of warm NOT HOT water (40°- 43°C / 104°-109°F).
Let stand 15 minutes without stirring, then stir well to suspend all the yeast.
Add to previously sulfited must. (The yeast should not be kept in the rehydration medium longer than recommended.)


The temperature delta between the prepared yeast and what it's going into is the same for both liquid and rehydrated yeast.

Most of us chill out wort/must at least to (if not below) the fermenting temperature before pitching the yeast so that things don't go ape-sheet right or give us nasty flavors. A small amount of higher temperature solution (~10C) will quickly be cooled to the same temperature of what it's going into. That's also why you don't want more than a 10C delta. You can easily shock/stress the yeast if they're suddenly put into a much cooler environment.

With dry yeast, the higher temperatures help with the rehydration process. Which is very different from the fermenting process.

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Old 01-01-2013, 12:18 AM   #6
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Yeast are fine in warm water but there is a limit to how warm. I think that limit is about 140F. beyond which the yeast die.

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Old 01-01-2013, 12:19 AM   #7
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Quote:
Originally Posted by BansheeRider View Post
I plan on doing that with my next batch, just wanted to make sure the high temps won't harm the yeast. I pitched dry yeast in my first batch and it was fermenting like crazy in under 8 hours.
Um, aren't you "re-hydrating" when you pitch the dry yeast onto the wet wort?

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Old 01-01-2013, 12:20 AM   #8
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Quote:
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Awesome graphic, should just sticky that..
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Old 01-01-2013, 12:21 AM   #9
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Quote:
Originally Posted by RM-MN View Post
Yeast are fine in warm water but there is a limit to how warm. I think that limit is about 140F. beyond which the yeast die.
Pretty sure that really only applies to dry yeast. I wouldn't want to put liquid yeast into anything even close to that. I have pitched a liquid yeast slurry into a wort that was about 10F lower than it's listed range. Fermented within a couple of degrees of the low end temperature for the duration. Batch came out great too.
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Old 01-01-2013, 12:22 AM   #10
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Quote:
Originally Posted by Satisfaction View Post
Awesome graphic, should just sticky that..
Found it here: http://www.lalvinyeast.com/strains.asp
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