From the HBD Archive
From: sherwood@adobe.com
Subject: bad beer
Date: 1992-03-02 17:12:51 GMT

Thanks for the many mail messages I received with regards to my friend's
beer. To recap, he had over 100 good extract batches, switched brewing
equipment and went all grain, then had 4 of 5 batches turn out to be
undrinkable due to a sour-milk sort of odor, all with stuck fermentations.

The consensus was underoxygenation causing the stuck fermentation, with the
bad odor and taste being a byproduct of that. I have two more data points.
When I tasted my (ie, not his) beer again (this time looking for that
off-taste) I found the same taste, though very slight. In addition, he finally
got around to dumping one of his kegs of bad beer. It had sat at about 45F for
two months. It was now HIGHLY carbonated. He sprayed maybe a gallon of foam
into his sink when he noticed something -- it didn't smell bad anymore. He
tasted it -- and immediately stopped dumping it. It now tasted just fine. I
had a glass; he was right. Not even a trace of the odor that was once so
overpowering we considered the batch a total loss.

So I have a conjecture. I recall mention here on the HBD of some chemical that
yeast produce while reproducing that they then reabsorb later. I thought that
that was a mild offtaste. Maybe not and that is what we have here? The stuck
fermentations perhaps preventing the reuptake?

On the latest batch, we oxygentated the wort fairly well and had it take off
like gangbusters. Very active fermentation, kicked off no doubt by a large
amount of pitched yeast (from a starter). But it still stuck, this time at
1030 but without the off smell of previous batches. He racked it to a
secondary, and fermentation picked up immediately (glub every 3 seconds). I
assume this was either to more oxygen or rousting the yeast. But he racks
gently to minimize oxygenation, and racks carefully to avoid racking the trub.
So if he didn't pick up much 02, and siphoned off only the yeast that was
already in suspension, why the dramatic increase in activity? In fact, would
oxygen help at this point at all? There was obviously enough yeast for a
vigorous start. So why do they stop? Do the yeast get 'tired' after a while
and require O2 either to get rejuvinated or to reproduce (so you get some new,
more vigorous yeast)? Do they just like the change of scenery ? (:-))

Any help with these questions is sincerely appreciated.

Geoff Sherwood

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