1-12. How is specific gravity related to beer?
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This article is from the rec.food.drink.beer FAQ, by John Lock with numerous contributions by others.
1-12. How is specific gravity related to beer?
Specific gravity is a measure of the density of a liquid. Distilled
water has a specific gravity of 1.000 at 60F(15C) and is used as a
baseline. The specific gravity of beer measured before fermentation
is called its Original Gravity or OG and sometimes its Starting
Gravity (SG). This gives an idea of how much sugar is dissolved in
the wort (unfermented beer) on which the yeast can work. The range of
values goes from approximately 1.020 to 1.160 meaning the wort can be
from 1.02 to 1.16 times as dense as water (in British brewing the
decimal point is usually omitted). When measured after fermentation
it is called the Final Gravity (FG) or Terminal Gravity (TG). The
difference between these two values is a good gauge of the amount of
alcohol produced during fermentation.
The OG will always be higher than the FG for two reasons. First, the
yeast will have processed much of the sugar that was present, thus,
reducing the gravity. And, second, the alcohol produced by
fermentation is less dense than water, further reducing the gravity.
The OG has a significant effect on the taste of the final product and
not just from an alcoholic standpoint. A high OG usually results in
beer with more body and sweetness than a lower OG. This is because
some of the sugars measured in the OG are not fermentable by the
yeast and will remain after fermentation.
Here are some rough guidelines:
Some Bitters, Milds, Wheat beers, and most "Lite" beers have an OG
ranging from 1020-1040. The majority of beers fall in the 1040-1050
range including most Lagers, Stout, Porter, Pale Ale, most Bitters,
and Wheat beers. From 1050-1060 you'll find, Oktoberfest, India Pale
Ale, ESB (Extra Special Bitter). In the 1060-1075 range will be Bock,
strong ales, Belgian doubles. Above 1075 are the really strong beers
like Dopplebocks, Barleywines, Imperial Stouts, and Belgian trippels
and strong ales.
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