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**helibrewer** · 12-22-2011, 04:37 PM

Don't confuse reproduction with respiration. There are 3 basic types of cell respiration; Aerobic respiration, Fermentation, and Anaerobic respiration. It's all about who's accepting electrons. Remember the Glycolysis->Oxidative decarboxylation of pyruvate->Kreb Cycle from biology class? Without oxygen, pyruvate goes through fermentation, the waste products being ethanol and CO2...and NAD+ to re-enter the glycolysis pathway...not a very efficient path for energy production but we're after the ethanol, not ATP :-)

**daksin** · 12-22-2011, 04:52 PM

Quote:

Originally Posted by helibrewer

Don't confuse reproduction with respiration. There are 3 basic types of cell respiration; Aerobic respiration, Fermentation, and Anaerobic respiration. It's all about who's accepting electrons. Remember the Glycolysis->Oxidative decarboxylation of pyruvate->Kreb Cycle from biology class? Without oxygen, pyruvate goes through fermentation, the waste products being ethanol and CO2...and NAD+ to re-enter the glycolysis pathway...not a very efficient path for energy production but we're after the ethanol, not ATP :-)

We're talking more about reproducing under anaerobic conditions because of the stress it puts on the yeast before real fermentation starts. It takes a lot of energy to grow and divide, and that energy needs to come from somewhere. You're absolutely right, though.

**weirdboy** · 12-22-2011, 05:05 PM

The short, less technical explanation is that your beer can develop all kinds of off flavors due to underpitching.

e.g. acetaldehyde, diacetyl, DMS, esters, fusel alcohols, vegetal aroma/flavor can all result from this.

Plumpie · 12-23-2011, 04:15 PM

Thanks for the insightful thoughts! I'll experiment with some extremely low doses of yeast to see what i'll get.

plumbob · 12-23-2011, 05:11 PM

You'll also increase the chance of infection by underpitching. Regardless of how well you sanitize some things you don't want it you beer, will get in there (a lot of them come off of you, and you don't really want to sanitize yourself!).

When you pitch an adequate amount of yeast, they take over and make a hostile environment for most critters to live in. They use up all the oxygen, create alcohol and eat food so fast most everything else just can't keep up. That gives you some buffer room so that even if a few thousand spores from some other bug make it in the wort (and the always always always will) they get out competed and die before they do any damage.

**daksin** · 12-23-2011, 06:01 PM

Quote:

Originally Posted by Plumpie

Thanks for the insightful thoughts! I'll experiment with some extremely low doses of yeast to see what i'll get.

Enjoy your poor tasting, underattenuated beverages!