I followed the same recipe as my usual kombucha, but using 1/2 cup of fine-ground, dark-roast Colombian coffee in place of tea. After brewing for 17 days, the fermentation was easily noticeable, but the coffee flavor was still prominent. Since I can’t really notice the tea flavor in my usual kombucha, I let it go a little longer to see if the coffee flavor would decrease. I tasted it again at 24 days and the acidity was getting a little overly strong without any abatement of the coffee flavor, so I decided to bottle it.
I left 1 quart plain, but I wasn’t sure what sort of flavors would complement this. I ended up making one of Bengal Spice and one of Chocolate Hazelnut. I figure if people will buy dirty chai or a hazelnut mocha, those pairings should at least be plausible in a coffee kombucha. I was surprised to find that, after bottling and refrigeration, the coffee flavor was virtually undetectable, though the overall flavor was rather strong and the color was much darker than usual. I’m guessing that this wasn’t a fair test of the compatibility of those flavors with coffee kombucha, so I suppose I should try them again. As it is, the Bengal Spice is drinkable, but not nearly as enjoyable in black tea kombucha, and the Chocolate Hazelnut is okay. I’m not especially fond of it, but it is only a light flavor on top of a kombucha base of which I’m not especially fond. The fact that it doesn’t make it worse is actually a good sign.
The jar this was brewing in seemed to lose more liquid than the others. The jar’s stick-on aquarium thermometer has consistently read 86°, I wonder if it’s been warmer than the others. I was surprised to find that the scoby was a little dried and small. it was stuck to one side of the jar, and that side was raised out of the kombucha from where the liquid level had gone down. I figure the poor scoby could have several causes:
- too hot for the cultures to form a good scoby
- Since 86° is still within the upper-end of what’s commonly accepted as a healthy range for the involved cultures, I’m not inclined to think that the problem is strictly the temperature.
- getting stuck to the jar caused the scoby dry out and form poorly
- This seems unlikely, but possible.
- coffee doesn’t support a strong, scoby-forming culture
- Some people report coffee producing quick fermentation and/or thick scobys, so the data is mixed on coffee itself being the issue. I suppose it’s possible that some cultures favor coffee more than others, so what works well for some people may not work well for others.
- elevated initial acidity stunted scoby growth
- Many coffee kombucha recipes recommend omitting the starter liquid from a previous batch of kombucha, with the rationale that the liquid is used to increase the acidity to the level needed by the yeast/bacteria in the scoby. Since coffee is already relatively acidic, the additional acidity isn’t needed.
The latter one is an interesting perspective, especially insofar as it’s the opposite of my current hypothesis that the scoby is by-product of the process that isn’t actually needed if starter liquid is used. I should try a batch of coffee kombucha with scoby but no starter, just to see how that works out. I can envision this leading me into a series of experiments using a scoby while replacing the starter liquid with a different acid. I happen to have malic acid handy, but it should be pretty easy to get citric, ascorbic, lactic, and tartaric acids form my local homebrew supplier.