Useful formulas for brewing

Knowing how many gallons of water you are boiling important to know but often difficult to measure.

This formulas gives you the number of gallons in a cylinder brew pot:

Pi x R2 x H / 231 = Gal

That means Pi (3.14) times the radius of the brew pot, squared, times the height on the water in inches divided by 231, the number of square inches in one gallon.

Example for a 4 gal, 12" diameter brew pot.

3.14 x 6 squared x 6 divided by 231 =
3.14 x 36 x 6 divided by 231 = 2.94 gallons

The other formula is how to substitute the grain in a recipe you like for LME or DME. 1 pound of grain = .75 pounde of LME = .6 pounds of DME.

These formulas have helped me out often. One tip is to record how many inches in your usual brew pots equal how many gallons. That way you can just run the faucet untill you hit the desired depth of water.

Skip the math. Knotches on a stick (or mash paddle) works perfect for me.

I'll take this opportunity to say that this hobby has given me an enormous appreciation for the metric system. Calculating with fl. oz., cups, pints, quarts, and gallons suuuuuuuuuuucks!!!

JonM said:

I'll take this opportunity to say that this hobby has given me an enormous appreciation for the metric system. Calculating with fl. oz., cups, pints, quarts, and gallons suuuuuuuuuuucks!!!

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Come on US, we gotta get on top of changing over to the system the REST of the world uses.

Sincerely,

A Nerd and Homebrewer

I love metric. I love the way you can convert water weight and volume directly. 1g = 1ml = 1cm3. 1 Kg = 1 litre = 1000cm3. 1 cubic meter = 1000 litres = 1 ton.

Works for beer to if you account for the gravity.... which is metric 20 litres of beer weighs 20 * SG Kilos. EG: 20 litres * 1.010 = 20.2 Kilos. That of course works backwards, if you don't have a hydrometer. If you beer (not including the FV) weighs 20.2 kilos and you know there is 20 litres, then it's SG is 1.010.

I hate imperial as it's all to do with King's feet and horses heights and what not.

One argument, over here, that I do feel holds merit is that imperial measurement should be taught at school, because having everything in "base 10" is so, so much easier, (can you say lazy), than imperial were everything has a different base making the math much more difficult.

Personally, I took up computer programming instead, so base 2, base 8, base 10, base 16 and even base 32 and 64 are common to my day job.

If you can handle a little algebra and have a good conversion calculator bookmarked, it's not so bad.

Metric is easier to do when you have a couple beers in ya.

Lbs of Grain x 5 = Approx starting gravity (5g batch, 70% eff)

10 lbs x 5 ~ 1.050

10 lbs x 37ppg x .70 / 5 ~ 50

Starting gravity x 4 = Approx billions of yeast cells needed
1.050 beer: 50 x 4 = 200 bn cells.
Double for lager.

.75million cells/mL/°Plato x 20k mL/gallon x .25 SG/°P = 3.75 ~ 4

TyTanium said:

Lbs of Grain x 5 = Approx starting gravity (5g batch, 70% eff)

10 lbs x 5 ~ 1.050

10 lbs x 37ppg x .70 / 5 ~ 50

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That doesn't work for those of us who get 89% efficiency now, does it?

bigbeergeek said:

That doesn't work for those of us who get 89% efficiency now, does it?

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No, but if you know you're getting 89% efficiency, there's no way in heck you'd rely on a simple formula like that. In your case, multiple by 6.5
More useful for new-to-AG folks I guess, to estimate grain usage.