From the HBD Archive
From: rutgers!vine.vine.com!polstra!jdp@hplabs.HP.COM (John D. Polstra)
Subject: Gelatin and Extended Fermentation
Date: 1989-10-26 16:14:55 GMT

Somebody recently asked about how adding gelatin to the carboy appears
to cause fermentation to start up again. In HBD #287, Dave Sheehy
(dbs@hprnd) replied:

> I don't think the gelatin has anything to do with this rather the mere
> act of agitating the wort rekindles the yeast into activity.

The gelatin definitely has something to do with it. I've made beers
both ways, and the ones with gelatin do a lot more foaming and bubbling
in the carboy. The same thing happens when I add dry hops to the
carboy, especially if I use hop pellets.

I'm sure the effect is *not* due to a resumption/revitalization of
fermentation, however. I left one of these brews in the carboy,
bubbling away, for three weeks once, and the SG didn't drop even a
point. If the SG is not dropping, the beer is not fermenting.

My theory is that the small particles of gelatin (or dry hops, or
stirred-up yeast in Dave's anecdote) provide a place for the dissolved
CO2 in the wort to collect and grow into bubbles which are large enough
to escape from solution. You can see the same effect if you toss a
teaspoon of salt into a glass of beer.

One time I brewed a batch of beer and I wasn't satisfied with the hop
aroma. As an experiment, I opened a bottle of the brew and dropped in a
single hop pellet, then re-capped the bottle. (This was supposed to be
dry hopping on a very small scale.) Just adding the hop pellet caused
some immediate foaming. When I opened the bottle a few days later to
taste it, a fountain of foam spewed out, emptying two thirds of the
bottle. Again, I think the effect was due to the fine particles causing
the CO2 to "preciptate" out of solution.

Bubbling rate is not a good indicator for when it is time to bottle.
It's much better to take SG readings and to bottle when the SG quits
dropping.

Relax, don't worry, have a homebrew.

-- John Polstra jdp@polstra.UUCP
Polstra & Co., Inc. ...{uunet,sun}!practic!polstra!jdp
Seattle, WA (206) 932-6482

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