I'm looking to measure my 'bucha's abv%... my question is if the data recorded with the hydrometer translates to abv% as it does with beer? Or, would there be a different equation to apply?
I'm sure with a little basic chemistry knowledge this is common sense... but that's just something I don't have...
asked byKashkillz (3452)
Get FREE instant access to our Paleo For Beginners Guide & 15 FREE Recipes!
on February 02, 2013
at 12:11 AM
No, it doesn't translate correctly.
The hydrometer readings taken before and after wine or beer fermentation are able to give an approximate abv% because nearly all the conversion is sugar into alcohol and CO2, and these give uniform, predictable result as they change.
With kombucha, the conversion is (usually) extremely light on the alcohol side and you have lots of other by products made, so I would wager that a hydrometer-abv% equation would yield a much higher result than you actually have.
I'm not sure if a vinometer would work, either. Assuming nearly all the sugars were converted so the vinometer could work at all, the other by products are bound to mess with the theory behind the vinometer: that the alcohol predictably interferes with the water's surface tension and the glass capillary it's in.
I'm not sure of any other easy home methods.
EDIT: I've had to add this information since some people don't understand the basic principles of wine/beer fermentation as well as the basics of kombucha.
Wine (or beer) pre fermentation is a juice (or mash). Water is added if the juice's sugar content is too high; sugar is added if the content is too low. The reason the sugar-strength is diluted or increased is because it is a control for two things: the residual sweetness of the wine (i.e. sugar left over) and the alcoholic strength of the wine. Both of these factors are also effected by the species of yeast used -- some types eat lots of sugar, produce more alcohol and CO2, and are able to survive longer in their own waste (i.e. fermentation continues longer).
The basic, physical approach to brewing kombucha is the the same as wine. You have a base (tea) to which sugar is added. However, instead of introducing yeast, one introduces the "SCOBY", which is an acronym, not a word: it means "symbiotic culture of bacteria and yeast".
Now, in general, the yeast are going to proceed as above with wine: they will eat sugar and produce CO2 and alcohol. If you took hydrometer readings before and after fermentation and used only yeast and not a SCOBY, you could calculate the hypothetical possible abv%. For common recipes for kombucha, I would estimate the theoretical maximum is 1-4% abv. (This is completely a guess.)
Now, if the story stopped there, you'd have your answer. However, it doesn't. The complementary bacteria in kombucha is acetobacter. Acetobacter is the bacterium that can ruin wines. It does this because it is an anaerobic bacterium species that eats alcohol and produces vinegar (technically it produces acetic acid). If you are making wine, you have to have good cleanliness and quality controls to avoid this. However, if you are making kombucha, you purposefully introduced acetobacter to digest the alcohol produced and produce vinegar and other by products.
It is the entirety of these by products for which kombucha is prized: trace alcohol, vinegar, and a plethora of proteins and vitamins produced by the yeast and the bacterium. There is certainly not 0% alcohol in kombucha, but the levels are most likely lower than a standard non-alcoholic beer (0.5% or so).
Summary of the edit: the equations for wine making that estimate potential abv% using specific gravity cannot be used to estimate abv% of kombucha.
on February 02, 2013
at 01:01 AM
How about not over thinking it and just enjoy it?
on February 02, 2013
at 12:12 AM
Yeah, I'm pretty sure it would be the same! Water is always heavier than alcohol, and sugar water is even heavier. So, I would just follow the same steps: 1. Measure with hydrometer/Calculate original gravity (OG) before fermentation 2. Calculate terminal gravity (TG) when degree of fermentation is reached 3. Alcohol content = ((1.05 x (OG ??? TG)) / TG) / 0.79