work in progress
--Kaiser 22:51, 25 November 2007 (CST)
Attenuation refers to the percentage of starting extract that has been converted by the fermentation process:
Attenuation = 100 % * (starting extract - current extract) / (starting extract)
This formula works with extract given in weight percentages and degree Plato. Since, at least in the wort and beer gravities that most brewers work with, there is an almost linear relationship between (specific gravity - 1) and extract percentages. This formula can be changed to:
Attenuation = 100 % * (starting gravity - current gravity) / (starting gravity - 1)
to work for brewers who measure extract as specific gravity.
To understand the different forms of attenuation we need to take a look at the extract composition first. During mashing, the majority of the grist is converted into water soluble compounds. This is shown in the diagram below.