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Old 11-26-2012, 04:07 PM   #1
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Default OK to harvest overpitched yeast?

Hello all

I kegged an IPA with Notty yeast, then dumped apple juice and 1 lb honey right back into the 5 gallon carboy. 24 hours later fermentation is blowing enough co2 out the airlock it is hissing, at first I thot a keg was leaking. Anyway, the juice may be a bit overpitched. Will this hurt the yeast for harvesting? The cider is the first reuse of the yeast.

Eric



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Old 11-26-2012, 04:43 PM   #2
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I over pitched a Sasion recently. After bottling the beer and saving the slury I took a look with a microscope. It's the most viable slurry I have harvested yet, and some of the least bacteria as well. Viable cell density was 1.4 trillion cells per liter.



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Old 11-26-2012, 06:52 PM   #3
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Overpitched yeast is understressed yeast, so it should be good. On the other hand, I have read that you shouldn't repitch cider yeast into beer. Since cider is composed of simpler sugars, the yeast are unused to fermenting more complex sugars (like maltose). This is why you make starters with DME, not apple juice or sugar water. This is also why people fermenting really big beers add the sugar after most of the fermentation of the malt sugars is complete to reach their desired gravity. I wouldn't harvest that yeast for beer use.

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Old 11-27-2012, 03:38 AM   #4
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Quote:
Since cider is composed of simpler sugars, the yeast are unused to fermenting more complex sugars (like maltose).
My knowledge on this issue is purely theoretical, but I would think this is at least partially true. Yeast do prioritize in order from simpler sugars to more complex, and while I wouldn't think one generation would make the yeast too "lazy" to ferment maltose, it probably isn't ideal.

Someone please correct me if I'm wrong though.
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Old 11-27-2012, 05:23 AM   #5
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The yeast book indicates that this is not a good idea. It isn't so much that overpitching hurts the beer, but it leaves it in a condition that is not good for future batches. Can't remember the deets. Maybe something about having not reproduced enough, or stearols or something....

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Old 11-27-2012, 05:40 AM   #6
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Pitching onto a cake doesn't give the yeast a chance to reproduce, so the cells end up old and tired. The beer doesn't taste so good either, as many of the flavor compounds we enjoy are produced during yeast reproduction. Making a Mr. Malty-approved starter from a small amount of the cake will allow for younger, healthier cells, as well as tasty esters and whatnot. Including malt in the starter will ensure that the yeast can metabolize maltose and maltotriose immediately. Making it from other sugars will result in a lag, but fear not; the yeast will eat the maltose and maltotriose eventually. If you let your beer sit for 2-3+ weeks as most of us do, you'll never know the lag existed.

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Old 11-27-2012, 05:15 PM   #7
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So overpitching makes the same yeast cells do all the work? Too many yeast cells for them to reproduce?

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Old 11-27-2012, 05:58 PM   #8
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When you repitch on a cake there is some cell division, but much less than when using conventional pitch rates. So yes, more of the yeast doing the work is old yeast. The low amount of cell division will produce less characteristic flavors. Also because of the higher amount of old yeast, there will be more dead yeast in the beer leading to more flavors associated with autolysis.



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