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Home Brew Forums > Home Brewing Beer > General Beer Discussion > "Yeast clean up after themselves"
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Old 02-07-2010, 05:00 AM   #1
DaveAllen
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Default "Yeast clean up after themselves"

I see this repeated numerous times here, but I'm not sure I understand the science behind this statement. Any enlightened responses?

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Old 02-07-2010, 05:32 AM   #2
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Yeah. I'd be interested too. People say to leave the beer in the primary for a month instead of using a secondary but what good are the yeast that have decided to go dormant and lay on the bottom?

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Old 02-07-2010, 06:47 AM   #3
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I am not familiar with that statement, but in fermentation, yeast produce several chemical compounds that they later reassimilate and metabolize. One such compound is diacetyl which gives beer a distinct buttery, butterscotch note. This maybe what is being referred to in this statement.

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Old 02-07-2010, 07:00 AM   #4
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as DM said, and other chemicls too.

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Old 02-07-2010, 07:01 AM   #5
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Interesting. Yeast "reassimilate and metabolize" diacetyl? That's fascinating. I'd love to hear more about that.

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Old 02-07-2010, 07:08 AM   #6
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Quote:
Originally Posted by DaveAllen View Post
Interesting. Yeast "reassimilate and metabolize" diacetyl? That's fascinating. I'd love to hear more about that.
Diacetyl rest brother. A process done to all lagers.
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Old 02-07-2010, 07:11 AM   #7
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Some metabolic sideproducts are utilized by the yeast after they have exhausted the simplest nutrient sources. Diacetyl and acetaldehyde are typical examples. There might be some metabolism of various esters, but probably to a minimal degree.

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Old 02-07-2010, 07:13 AM   #8
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Aceteldehyde also. It's part of the process to making ethanol. Racking yeast too early will leave that green apple characteristic.

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Old 02-07-2010, 07:44 AM   #9
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It's important to note that only healthy yeast will "cleanup" fermentation byproducts (i.e., chemically convert a certain percentage of undesirable chemical compounds with a low flavor threshold to one or more compounds with a higher flavor threshold).

For example, if you conduct a poor fermentation (e.g., significantly under-pitching), the yeast will not be able to reduce the offending compounds to a satisfactory degree.

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Old 02-07-2010, 08:24 AM   #10
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i don't notice any flavor concerns when i pitch about 250-500mL worth of yeast slurry per 5 gallons. yet when done we get over 2L of slurry. which tells me that is "under" pitched if there is such a thing. i bet one has to just add the smack pack to 5 gallons to have any issue with that?

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