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Brews & Views Bulletin Board Service * Brews and Views Archive 2004 * March 16, 2004 * Estimating percent alcohol without OG < Previous Next >

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Sean Richens (
Posted on Tuesday, March 02, 2004 - 03:41 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I have a traditional African homebrew that I'm presenting at Wednesday's club meeting. Even among brewers, I expect someone will ask if I have any idea of the percent alcohol.

Since the beer is made directly from solid starting materials, with hydrolysis of the starches taking place simultaneously with fermentation, there never was an OG to measure.

Has anyone ever run across a formula to estimate alcohol from the apparent extract and real extract? Or, in gravity terms instead of Plato, if I calculated
AG - (RG-1)
with AG and RG meaning what you expect, I would get a number just less than 1. Would that be a rough estimate of the SG of the corresponding alcohol/water solution?

Fredrik (
Posted on Tuesday, March 02, 2004 - 10:46 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I figure you have to know the residual extract, aside with the FG, otherwise it's not possible to calculate the alcohol.

Maybe you can boil a sample, and get it completely dry, and check the mass before and after, then you can calculate the RE as residual mass/initial mass? I haven't tried it but if you have a good scale maybe it will work as an estimate?

I've got a formula for calculating alcohol if you know FG and RE. It may possibly differ from other formulas but it should give you the ballpark alcohol anyhow.


Maybe another option would be to try and boil off the alcohol only and measure the lost mass to find the alcohol directly without knowing the RE, if that is easier?
I don't know which would be the most accurate method.


Sean Richens (
Posted on Wednesday, March 03, 2004 - 12:20 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Thanks, Fredrik. I'll try your formula, if only to test it for future use.

I found a couple of spreadsheets on line that give ballpark estimates of real extract based on keyed in original gravity and apparent final gravity values. I can just poke in OG values until I get a pair of results that make sense and see what it estimates the ABV to be.

craig white (
Posted on Wednesday, March 03, 2004 - 12:36 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

post the recipe.

Sean Richens (
Posted on Wednesday, March 03, 2004 - 04:33 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

OK, if you're sure you're brave :).

It's called Suwa in the Tigrinya language, or Tella in Amharic. This is a wild-fermented beer so you must not use any plastic items that will contact regular beer. I use retired equipment or glass and stainless.

You will have to find an herb called Gesho. It's native to Eritrea and Ethiopia, and is pretty tough to track down. Washington DC is the obvious place to try, L.A. and NYNY should be good, I've heard rumours of it being available in Minneapolis. I got mine in Kensington Market in Toronto. You want the leaf (for beer) not the bark (for mead). An acceptable fake would be some old hops (like for Lambic) and some yellow birch twigs and/or bitter orange peel.

First, take 2 lb Tef or millet flour, add water to make a thin batter and cook as crepes without oil. This is going to require a really good non-stick pan. These could be dried but I just freeze them until needed.

I cheated and made a sourdough starter using 1 cup Tef flour and water, kept in a warm place for 36 hours. This is, in fact, injera batter if you know the cuisine of the Horn of Africa countries.

Second, Crush 2 lb. pale malt and 1/2 lb. medium crystal or amber malt. Chop 2 lb. dried dates. Place these two ingredients in pail with 4.5 US Gallons cool water. Add 2 cups powdered Gesho herb. You're not supposed to add any yeast, but I hedged my bets by adding the sourdough starter.

After 5 days fermentation (about 60F), thaw out the crepes, tear them up small and add them to the batch.

After another 5 days fermentation, strain the solids out with a coarse colander. This is a miserable step. The solids will plug cheesecloth! Racking is too effective, you want the fine gritty solids in the final product.

And finally, let the cloudy liquid ferment a few more days. It will start to sour, and be about right between 3 and 4 days after the straining. Some people like to bottle it so it gets a bit of a fizz. The excess can be frozen, but of course it won't be fizzy when thawed.

If you know anyone from Eritrea or Ethiopia, I highly recommend recruiting them, even if it's only to help drink the final result.

Fredrik (
Posted on Wednesday, March 03, 2004 - 05:54 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Sean, you don't have any bubble data by any chance? One could maybe make a very crude ballpark estimate of alcohol from the peak rate, lagtime and at one or two late readings.


Mike Kidulich (
Posted on Wednesday, March 03, 2004 - 05:11 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Check your LHBS for a Vinometer. They only cost like $5. It's used to measure alcohol content of wines. It's not really accurate with sweet wines, but works well for dry wines. I think they are intended for still liquids, so you may have to de-gas your sample.

Drew Avis (
Posted on Thursday, March 04, 2004 - 09:52 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Mike, vinometers are notoriously inaccurate, and probably even less accurate at lower %alc.

Sean, do you have access to a refractometer? If you can take the brix reading from the refractometer and a specific gravity reading, you can calculate (roughly) the % alcohol.

Sean Richens (
Posted on Friday, March 05, 2004 - 03:51 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Well, I tried various rough formulae obtained here and there. From an apparent gravity of 1.007 and a real gravity of 1.013, and assuming that the sugar-ethanol interaction is minimal (both concentrations are reasonably low), you could consider the volatile portion of the beer to be SG 0.994, which corresponds to about 4% ABV. The other methods I've tried so far give results in the 3.5 to 4.5% range.

The real gravity reading may be low, since a lot of material coagulated while boiling off the alcohol. Even so, the percent alcohol estimates put the OG up in the 1.040 range, which means about 80% brewhouse efficiency! Shows what a 10-day mash can do for you.

This has all been instructive, and I'm sure I'll be able to use this in the future for country wines and other difficult-to-assess starting worts and musts.

Sean Richens (
Posted on Friday, March 05, 2004 - 03:53 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Oh, and a P.S.: No-one actually asked the alcohol content of this beer! One member asked about the alcohol content of the chicha I served in the same presentation, but he was wondering about the flavour more than the buzziness.

Doug Pescatore (
Posted on Friday, March 05, 2004 - 01:25 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

How did this "beer?" taste?

Sean Richens (
Posted on Saturday, March 06, 2004 - 06:42 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

You'd have to actually try it to describe it. The wintergreen-citrus flavour is from the herb, and is quite subtle. Since I managed to avoid getting oil into it this time it didn't have the cheesy aroma, so it comes out as a refreshing sour-beery (less sour than a lambic or contaminated batch) grainy drink. I suppose all things considered, the grainy flavour dominates.

Chicha is sweet, corn-y almost soda-pop-hold-the-H3PO4 flavour. It is certainly acceptable to the North American palate, but doesn't have a counterpart in our beverage list (Singapore Sling, maybe?) which makes it hard to introduce to the timid drinker.

As far as alcohol content goes, I did the "bioassay" and had a full beer glass of each. The torque test (i.e. how much does my head spin) puts the alcohol level easily over 5%.

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