The most-recent episode of Basic Brewing Radio has got me thinking about making Kombucha.
What would be a typical OG (original gravity) and FG (final gravity) for a Kombucha?
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I get over a million hits for "kombucha fg" on Google...– RobertMay 17, 2017 at 16:05
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@Robert: And do you easily find the answer to my question from those hits? Here's something from the very first hit I got with your search: "There doesn't seem to be much technical information on OG and FG for kombucha." I got that same link in the results of a search I did yesterday, before I asked my question here.– Jeff RoeMay 17, 2017 at 16:16
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1@Robert If the question isn't already on Stack Exchange then it's a perfectly valid question. There's a reason there's an answer your own question button. Stack Exchange strives to be as exhaustive a source as possible for many different topics, and often stack exchange questions end up among the first results from Google.– bendlMay 24, 2017 at 21:06
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1I am a home brewer, beer and kombucha. Maybe I can weigh in as a chemist. Specific gravity is the weight of the liquid. Pure water is 1.0, by definition. As chemicals are added the water gets heavier. Most everything does this; alcohol, acetic acid, lactic acid, almost everything. The OG for kombucha would be essentially all from sugar. So, it would be meaningful. (the tea component would be negligible) The FG would be too complex for any simple interpretation. I just checked the OG for next month's batch for kombucha. 1.02 (that would be grams per milliliter) Looks okay.– JohnMay 6, 2018 at 22:37
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2 Answers
Suggested OGs are around 1020-1030 from a number of forums, but people are making big 1090 OGs.
Regarding FG I recall they end quiet dry as there is often only simple sugars and very little tri-saccharides or longer polysaccharides. so I would expect around 997-1004. What little I can find on the google seems to agree, I have a book at home I will dig it out this evening and see if it sheds more light on this.
Edit: As noted below, you cannot use the OG-FG to calculate Alcohol for Kombucha as it is then further transformed into acetic acid but the acetobacteria in the SCOBY.
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Interesting. It seems to me that a Kombucha that went from 1.020 to 1.000 would be about 2.5% abv. And yet the commercial Kombuchas I've seen are claiming to be less than 0.5% abv. I'm struggling to understand this huge difference.– Jeff RoeMay 18, 2017 at 1:33
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Side note: 1.090 is not an attempt at Kombucha. Those folks are making tea flavored hooch!!!– brewchezMay 18, 2017 at 15:27
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2@JeffRoe - Kombucha is an aerobic ferment, and the mother contains acetobacteria. The sugar is fermented into alcohol, but rather rapidly further fermented into acetic acid (vinegar). May 18, 2017 at 19:56
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My recipe
- 1 cup sugar (5.7 oz)
- 6 liters water (1.58 gal)
- 1/4 cup loose black tea
I've never measured the OG or the FG, but the recipe calculates to OG 1.014.
The reason why I've never measured the FG is because I just tasted it every so often, and pull it off the SCOBY when it tastes right to me. There is no reason to having booch that's too sweet or too sour; when you're making it yourself, just taste.
Tasting is simple for me. I went and got a 2 gallon frosting bucket at the grocery store, put a tap on it, and voilà, I had a kombucha machine!
