Quick Lesson: How to use a Pearson's Square

Written by DJ Spiess

Thursday, 03 January 2008

Are you looking to fortify your fermented beverage, but are uncertain how much spirit to use? This guide will tell you exactly how much to add.

The easiest way to calculate the amount of alcohol required for fortification is to use a Pearson’s Square.

Pearson's square for fortifying beverages

First determine the alcohol strength of the wort or must that you want to fortify. You can do this by measuring the specific gravity before and after fermentation. Once you have the alcohol strength, place that number in position A.

Next note the alcohol strength of the fortifying spirit in position C. This is the alcohol strength of the brandy, whiskey, or Everclear that you are adding.

Decide the final alcohol strength you are targeting for your fortified drink. This number should be between the values chosen for A and C. This number should be placed in position X.

Calculate B and D. B is the difference between C and X (C – X). D is the difference between X and A (X- A).

Finally take the ratio of B over D (B / D). This is the ratio you will use to add to fortify.

The Pearson's square is very easy to use.

Here are the steps with an example:

1)   Determine A – Assume your initial alcoholic strength is 10%.
2)   Determine C – Assume you are using 180 proof alcohol which is 90%
3)   Determine X – Assume we are targeting a 25% beverage
4)   Calculate B – (B = 90 – 25 = 65)
5)   Calculate D – (D = 25 – 10 = 15)
6)   Calculate the ratio B/D – B/D = 65/15 =13/3

13/3 is your final ratio. This means for every 13 parts of your initial beverage, you need to add 3 parts of your fortifying spirit. For example if you had 39 liters of wort, you would add 6 liters of your fortifying spirit.

[Edit 5-19-2008: Corrected values]