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Pearson's Square
Pearson's Square is a method for determining the relative amounts of wine and fortifying agents (ie vodka, brandy, grain alcohol, etc) to use to increase the alcohol content in the wine to a given amount. The only required information is the alcohol content of both the wine and the fortifying agent, as well as the desired alcohol content. It makes no difference what scale you use for the alcohol content (U.S. proof, Syke's, or % alcohol) except that Brittish proof must be converted to degrees Sykes by adding 100.
To lay out the square and do the calculations by hand use the following instructions:
A D
C
B E
A - C = E
C - B = D
Where:
A = Alcohol content of the fortifying spirits
B = Alcohol content of the wine
C = Desired final alcohol content of fortified wine
D = Parts of fortifying agent in fortified wine
E = Parts of original wine in fortified wine
For example:
If you use vodka (40% alcohol) as the fortifying agent and wine with an alcohol content of 12% which you want fortified to %18 alcohol:
40 6
18
12 22
40 - 18 = 22
18 - 12 = 6
You would use 22 parts of wine and 6 parts of vodka to obtain a fortified strength of 18% alcohol.
Note:
This can also be used to determine quantities for dilution. (The above example could be considered as diluting the vodka from 40% to 18%.) When diluting with water, just use 0 (zero) for the alcohol content.