3 Basic Homebrewing Formula's

I like to keep accurate notes on the batches of beer I brew. Primarily to use as a reference to repeat recipes I really enjoy and also to modify those recipes that I think need a little tweeking to get just right.

To help me do this, it is important for me to know a couple of things that occurred during the brewing and fermentation of the beer. The following are 3 calculations I use in my process.

1. Efficiency - how effective I was at extracting the grain sugars


2. Attenuation - how well the yeast fermented those sugars in the wort


3. Alcohol by Volume - percentage of alcohol in the beer by its volume

The efficiency is important to know because it tells me the sugar extractions that I normally get from my mash and then I can use that information when making ingredient quantity changes. The following formula will tell me how much of, or what percentage of available sugars from the grains that I should expect to get from my system.

For instance, 1 lb. of 2-row has the potential for a gravity of 1.037 in a gal. of water. By then dividing the actual measured gravity of the wort by the potential, it will equal the efficiency or percentage of extracted sugar I attained.

That is, if the measured gravity of the wort is 1.029 or 29 divided by the potential sugar of the grain, let's say it's 1.037 or 37 I get 78%.

(29 divided by 37 = 78%)

To take it a step further,if I am brewing a 5.5 gallon batch of beer and collected 6.5 gallons at the start of the boil, I will measure a sample of the wort and multiply by 6.5 to get my gravity reading. I will then divide that gravity reading by the accumulated potential sugars from the grains that I mashed. For example:

10 lbs. 2-row @ 1.037 = 370

1 lbs. cry#60 @ 1.034 = 34

2 lbs. aromatic @ 1.035 = 70

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for a total potential extraction of 474

We'll make an assumption that the gravity measures 1.058 or 58
multiply that by 6.5 gals.to get 377 then divide by 474 to get 79% efficiency.
After using this calculation on numerous batches I now can develop recipes based on the knowledge of the extractions I normally get from my brewing regime and system.

Attenuation percentages are the result of the difference of the gravity of the beer at the beginning and end of the fermentation process. I will also use these numbers to find the alcohol percentage. This is done by subtracting the final gravity (f.g.) reading from the original gravity (o.g.) and then dividing the final reading by the original reading. For example:

If the O.G. is 1.058 and the F.G. is 1.012 you will subtract 1.012 from 1.058 to get .046 then divide .046 by the O.G. of .058 to get 79% attenuation.

Alcohol is finally, figured by taking the .046 that I got from subtracting the F.G. from the O.G. and multiply it by 105 to get 4.83 and add 1.25 to get the alcohol by volume of 6%.

Hopefully this has helped more then confused. Let me know in the comments below.