OG vs FG

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Local homebrew store owner today told me that the FG is roughly a certain %
of the OG. Im curious, as Ive been making some of my own recipes now, and Im
not sure what to look for as my target for FG. She said its about as good as
it'll get, (OG 86, currently 20). Anyone have input on this?

Re: OG vs FG
The one thing that I've noticed, that pretty much everyone can agree on,
is to take readings for three days, if the gravity doesn't change you've
reached the end.

White Trash wrote:

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Re: OG vs FG
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When brewing with extract (rather than mashing all the grain yourself),
typically the gravity will end somewhere around 1.020, due to unfermentable
sugars in the extract.  So your shop owner is probably correct.  But as
another person said, check the gravity, wait a couple of days, then check
again.  If the gravity hasn't changed at all, then you'll know for sure that
fermentation is complete.  Especially if your OG was 1.086, I'm sure you
won't get much lower than 1.020.  This brew will be high in alcohol!  What
kind did you make?

"Just a drink, a little drink, and I'll be feeling GOOooOOooOOooD!" --  
Genesis, 1973-ish

Re: OG vs FG

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The intent was a fairly high alcohol content, the idea was to make an
approximate clone of an imperial stout that was about 7.8%:

1.25 lb chocolate
.25 lb roasted barley
.5 lb crystal
8.8 lb liquid munich amber malt
2.7 lb wheat DME
8 oz malto-dextrin
centennial (bitter)
kent goldings (bitter) total hbu = 11.3
.5 oz cent, flavor
.5 oz kent golding, flavor
and some hop for finishing/dry hop

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Re: OG vs FG

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It is only VERY ROUGHLY a certain %... because different extracts have different
amounts of fermentable vs. unfermentable sugars, and therefore, will ferment
down a different amount.  This difference can be considerable.  Also, some
yeast strains will ferment more aggressively than others.  Another example
is that Lager yeast can ferment an extra type of sugar that ale yeast cannot,
therefore lager yeast should ferment a little further than ale yeast.  Other
additives, like maltodextrin and crystal malts, will not totally ferment out
and, therefore, raise the FG higher than expected.

With all the variables, I don't think you can count on figuring the FG simply
by using a % of the OG.  The only exception might be if you always use the
exact same ingredients and derive the % from experience.

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