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Author Replies
09/13/10 09:50 PM  
Alcohol content in sour beers
Most beer recipe software programs calculate estimated % alcohol of finished beer. I'm curious as to whether souring makes a significant difference. Alcohol is a fermentation byproduct of yeast. Some acid (lactic at least) is a fermentation byproduct of the souring bugs (and some yeast). Do the bugs steal potential alcohol production by yeast? My suspicion is that the bugs are primarily using food the ale yeast can't use anyway, so the calculated alcohol content would not be changed by much, but this is just a hunch. Do any of the common bugs produce alcohol in addition to acid? Anyone have some data or other insight?
09/14/10 07:02 AM  
Re: Alcohol content in sour beers
At 't Brugs Beertje last March I had a Rodenbach Vin de Cereale, it was listed as a barley wine. 10%!!
09/14/10 08:59 AM  
Re: Alcohol content in sour beers
I've done brett only fermentations that started at around 1.80 and finished about 1.012. If brett produces the same amount of alcohol as sac yeast, then this beer was about 9% abv. But I have no idea if it was actually 9%, or 8% alcohol and 1% other acids and byproducts, or some other combination. My limited searches haven't found any data either, or at least data that my brain could comprehend.
Mike T
09/14/10 12:02 PM  
Re: Alcohol content in sour beers
It depends what strains you have at work. I was surprised that the beer I soured pre-boil with lacto grown up from grain only dropped ~.003 before over three days. If the bugs donít produce CO2 or another gas that leaves the vessel the gravity wonít drop. There are some specific strains of lactic acid bacteria that do create CO2, so if you have them the same OF>FG will result in a lower alcohol. Acterobacter gains energy by converting alcohol into acetic acid with the addition of O2, so I guess it could theoretically raise the gravity of the beer as it works.

Not sure that answered anything, but I donít think any of those are enough to throw off your measurements enough to worry about.

09/14/10 02:24 PM  
Re: Alcohol content in sour beers
I've had several strong sour beers, just to name a few, RR Toronado 20th, Consecration, De Dolle Oerbier Special Reserva (Had lots of times, but more recently also at 't Bruge Beertje :)), a couple homebrewed sours. Point being that it can certainly be done to "normal" beer strengths. I've had up to about 12%
09/14/10 03:20 PM  
Re: Alcohol content in sour beers
As was said, acetic acid is produced from alcohol, and lactic acid is produced from sugar, so gravity readings are misleading.

I wonder if brett byproducts are similar to sacch in that brett fermentation yields the same percentage of alcohol output.

For instance, if sacch yeast outputs 50% alcohol and 50% C02 (fictitious numbers) per weight of sugar, what does brett do? The same?

Sorry, I'm all questions and no answers.

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Around Bruges in 80 Beers: 2nd Edition

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