Date: 1992-06-01 20:52:02 GMT
Subject: Calories in Beer (George Fix)
I hope it was clear from my original post on calories that the formula
quoted was not due to me. It is something that has been floating around
for a few years. I found out about it at a local MBAA meeting from some
folks at AB-Houston. An older and somewhat less accurate version can be
found in Vol. 2 of Malting and Brewing Science by Hough,et al.
One of the legacies passed on to homebrewing from home winemaking has
been the use of specific gravity as a unit for expressing extract. For
wines this makes a good deal of sense as all of the technical research on
wine has used these units. Unfortunately, all the work on beer uses different
units, namely % extract on a weight to weight basis, or degrees Plato if
you like. The only time specific gravity is used is to convert numbers
involving weight to ones involving volume. For example, in the formula for
calories the specific gravity of beer multiples the entire term. Without
it the formula will give the number of calories per 1/3 kg. of beer. With
it we get the number of calories per 1/3 liter, or approximately calories
per 12 oz.
What is truly unfortunate is that there no simple way of going back and forth
from specific gravity to degrees Plato without directly looking them up in
the extract tables. Sometimes the factor of 4 is cited, and it does work for
some values. Thus a wort which is 12 deg. Plato has a specific gravity of
1.048, and 48 = 12*4. A quick glance at the extract tables shows the number 4
does not give very good results for other values. What this means is that the
classic beer formulas like Balling's and others can not be accurately expressed
in terms of gravities. In fact, most of the formulas I have seen which use
gravities have come from winemaking. They work well there, but they are highly
suspect when applied to beer.
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