Underpitch theory

Spintab · 08-07-2011, 04:21 PM

Been brewing for about two years now and until I made my first starter every single batch has had that oxidized tasting homebrew twang. The difference was night and day. So I have this theory floating around inside my beer infused brain. If you underpitch you are over stressing your yeast to reproduce and they are not able to consume all the O2 that you shook or blew into your wort.

Does this make sense to anyone or is it possible for yeast to consume all the oxygen in your wort regardless of how little you pitch?

I should add, I've gone through just about every other step of the process to weed out problems. I brew all grain, hit my temps pretty regularly, my efficiency is normally in the mid 70's, I ferment nice and cool in a temp controlled chest freezer, and my sanitation practices are good. I'm very careful not to shake my wort around and the only time it is exposed to air is during bottling. The black IPA I made a starter for is friggin fantastic, so I think it's pretty safe to narrow it down to the use of a starter.

**seabass07** · 08-07-2011, 04:27 PM

Are you sure it was an oxidation flavor? Underpitching will produce much higher esters. I'd be surprised if they couldn't suck up all of the oxygen though.

Calder · 08-07-2011, 04:43 PM

Under-pitching can produce some undesirable flavors, and increase the fusel alcohols. It will also stress the yeast, with the potential the beer will not fully attenuate.

The yeast will almost certainly scrub all the O2 you put in the wort. I suspect you are not tasting oxidation (wet cardboard, and/or sherry like flavors). However, your problem may be from under-pitching.

Spintab · 08-07-2011, 04:47 PM

To be honest, it's been described to me by other brewers as oxidized but now that you mention it, to me it is more of an estery flavor. Kinda like fruity sweat.

pissgarn · 08-07-2011, 06:30 PM

Quote:

Originally Posted by Spintab

Been brewing for about two years now and until I made my first starter every single batch has had that oxidized tasting homebrew twang. The difference was night and day. So I have this theory floating around inside my beer infused brain. If you underpitch you are over stressing your yeast to reproduce and they are not able to consume all the O2 that you shook or blew into your wort.

Does this make sense to anyone or is it possible for yeast to consume all the oxygen in your wort regardless of how little you pitch?

My theory is: excess o2 reacts to form triangles:

http://en.wikipedia.org/wiki/Epoxide

Triangles don't taste good:

1) Ripped the triangle off a bass ale bottle, it didn't
taste good (tasted like aluminum foil and glue).

2) Triangular Lego didn't taste bad, but couldn't
swallow it.

3) Triangles of cheese taste like cheese, which doesn't
taste good in liquid beer form.

Ron

Spintab · 08-08-2011, 02:45 PM

Are you suggesting that excess o2 forms epoxy in beer?

ayoungrad · 08-08-2011, 02:49 PM

Any oxygen left in the wort from the time of pitching should be displaced by CO2 produced by the yeast.

I'm with the triangle guy.

**GodsStepBrother** · 08-08-2011, 02:56 PM

I recently did a lot of research on the subject and describe what I found and get some feed back on this thread.

http://www.homebrewtalk.com/f128/exact-causes-yeast-stress-256467/

I think the main problem with under pitching comes from a long lag time, that can open up the gates for infection.

And excessive yeast budding, this causes a lot of virgin yeast to be in the beer that apparently are not good for fermenting. Also since all the yeast have budded so much they are full of scar tissue that forms a thick layer of of scar tissue on the membrane causes them not be able to eat from said point. If enough scar tissue is produced a yeast cell can literally starve in a nutrient rich environment, or will have to work twice as much to eat. Stressing them out.

**Bensiff** · 08-08-2011, 03:21 PM

Quote:

Originally Posted by GodsStepBrother

And excessive yeast budding, this causes a lot of virgin yeast to be in the beer that apparently are not good for fermenting. Also since all the yeast have budded so much they are full of scar tissue that forms a thick layer of of scar tissue on the membrane causes them not be able to eat from said point. If enough scar tissue is produced a yeast cell can literally starve in a nutrient rich environment, or will have to work twice as much to eat. Stressing them out.

I'll take this a step further, if you are underpitching you are getting excessive yeast growth, which will require a lot of oxygen for cell wall health. Not only are you using all your oxygen, you probably are giving it too little oxygen if you are not injecting pure O2.

pissgarn · 08-08-2011, 07:46 PM

Quote:

Originally Posted by Spintab

Are you suggesting that excess o2 forms epoxy in beer?

Yes, and the epoxy glue is what causes the yeast to stick to
everything.

Ron