From the HBD Archive
From: Marty Albini <hplabs!hpsdl39!martya>
Subject: predicting FG
Date: 1989-12-19 05:01:50 GMT

A few issues back I commented on some beer of mine that was
taking too long to ferment out. The question was raised: how do you
know when it's finished? How low the gravity will get? My usual
method is to look there at the end of the recipe where it says "FG="
and use the author's experience.

But what if it's a new recipe, or one without such a handy
guide?

Burch (_Brewing_Qualty_Beers_) gives a formula for computing
FG from the OG, which works surprisingly well considering its
simplicity. In short:
Projected FG= 1+(OG-1)/4
Obviously the unfermentables should have some impact on this, and a
stout with several pounds of black grains should finish somewhat
higher than an all-malt beer with the same OG. I've tried correcting
for this with various tables, but the formula seems to work best
as-is, at least with the last couple entries in my brew log.

This bothers me. I'm not worried, mind you, but it seems like
there ought to be a better prediction method; one that takes into
account things like the yeast's attenuativity (what a word! Did I make
that up or what?), unfermentables, and whatever else there is that
matters.

Why not just RDWHAH? If you stop too early and prime while the
beer is still too sweet, you get little glass grenades. I've never
experienced this delightful occurance, and never want to.

This seems to be a topic of broad interest; if somebody has a
reliable prediction method, please post!

Merry Xmas!
- --
________________________________________________Marty Albini___________
"To enjoy the flavor of life, take big bites. Moderation is for monks."
phone : (619) 592-4177
UUCP : {hplabs|nosc|hpfcla|ucsd}!hp-sdd!martya
Internet : martya%hp-sdd@hp-sde.sde.hp.com (or @nosc.mil, @ucsd.edu)
CSNET : martya%hp-sdd@hplabs.csnet
US mail : Hewlett-Packard Co., 16399 W. Bernardo Drive, San Diego CA 92127-1899 USA

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