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Old 12-30-2010, 04:05 AM   #1
martinworswick
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Default is oxygen necessary when using slurry?

i brewed a belgian pale a couple of days ago and used yeast slurry i took from a previous batch that i bottled whilst cooling the new batch.i checked mr malty for the required amount,measured it,dumped it in the new fermenter,added a gallon or so of wort,gave a good old shake and swirl,another gallon,repeat until its to heavy to bother and let the rest of the wort splash into the fermenter,whilst doing this i was idly wondering,is the main use of oxygen reproduction? if so then when adding the correct amount of slurry does the yeast need to reproduce?if it doesn't then have i actually overpitched?

enlightenment welcomed

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Old 12-30-2010, 07:17 AM   #2
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Yeah, about as much as if you were pitching a properly-sized starter. You want yeast reproduction and growth to provide some esters and flavors to beer (this is true even in the cleanest lagers).

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Old 12-30-2010, 02:07 PM   #3
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interesting question. i've always towed the party line that aerating wort should be standard practice. but i just saw a post in another thread that said oxygen deprivation can lead to more ester production. i wonder if there could be an instance where you would want to skip aeration to encourage more ester production. more questions, no answers

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Old 12-30-2010, 02:29 PM   #4
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I'm fairly certain that both indigi and Powers are correct. The oxygen helps the yeast reproduce by helping the lipids in the cell stay pliable. Under oxygenation does lead to to more esters, but I believe that is at the expense of alcohol production.

In my opinion, the best way to get more esters out of a beer is to underpitch a little bit.

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Old 12-30-2010, 02:49 PM   #5
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the only time i actually focused on getting some esters produced was on a belgian saison i made last summer. i fermented it at 80 degrees and it was quite fruity, without adding fruit. i did aerate and pitched a very adequate amount of yeast, so my guess is the higher temps allowed some esters. but then again, perhaps it was the Belgian yeast strain i used and the temps wouldn't have mattered.

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Old 12-30-2010, 04:38 PM   #6
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Quote:
Originally Posted by Powers View Post
the only time i actually focused on getting some esters produced was on a belgian saison i made last summer. i fermented it at 80 degrees and it was quite fruity, without adding fruit. i did aerate and pitched a very adequate amount of yeast, so my guess is the higher temps allowed some esters. but then again, perhaps it was the Belgian yeast strain i used and the temps wouldn't have mattered.
I know what you mean. I think it might be more the strain than the temp, since I've been having the same thing happen with my hefewizens. Different temps, same results. I know that temp does affect the amount of esters in a beer, but I'm beginning to think that the temp only equates to a not to detectable amount more of those esters (obviously off flavors are affected by temp too).

It may be more what kinds of enzymes and/or compounds get actived and/or produced during the mash that contribute to esters as well.
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