I’ve tried making anaerobic kombucha before, though with minimal effort to prevent aerobic fermentation. This time I took reasonable efforts to keep oxygen out, and I ended up with something rather different from my usual kombucha.
My brother had an amber growler with a stopper and airlock, and generously loaned them to me for a long-term kombucha experiment. Due to the narrow neck, I omitted a scoby, adding only 1/2 cup of my scoby hotel starter to my sweet tea base. I filled the growler, added the rubber stopper, and topped it off with distilled water. I then inserted the airlock and could see that some of the nascent kombucha had risen into the stem of the airlock. This was intentional, to visually confirm that the actual surface for oxygen exposure was minimized, and to confirm that it was reasonably sealed (no drips!). I added distilled water to the top of the airlock to create a one-way valve so that CO2 could escape without oxygen getting in, and let it sit off of the heating pad. I probably could have sped thing up by keeping it warm, but my experiments aren’t usually heated, and I didn’t want to dedicate the space for a long time.
I took regular samples by removing the airlock and inserting a straw into the stopper. I then I topped it off with distilled water to remove any oxygen that my have gotten into the growler headspace.
- 3 weeks: pH was 4.0, but the flavor was very watery with no sweetness, sourness, or even astringency.
- 6 weeks: pH was still 4.0, but the flavor had a slight sweetness (still very watery). It had a very lively effervescence with large bubbles.
- 8 weeks: pH was 3.6, and had developed a slight tartness, but otherwise taste the same as last time. It had a very lively effervescence with large bubbles, and I predicted it would be pretty interesting when “finished”.
- 12 weeks: pH was still 3.6, with the same thin slightly sweet watery flavor, but the faint tartness had vanished.
- 16 weeks: pH was still 3.6. The flavor was thin and mild, with a slight sweetness and astringency, but no tartness. The flavor reminded me of a very weak ginger ale. It had a very lively effervescence with large bubbles. After 4 months, I called it done. Due to a variety of family activities, this wasn’t actually bottled until 20 weeks, but I didn’t measure or evaluate anything at that time.
Based on what I’ve learned over the last year’s research and experiments, I’m not too surprised that the tartness appeared and disappeared. I am, however, surprised by the disappearance and reappearance of sweetness. Nonetheless, these were subjective observations, and it’s possible that the different perceptions were due to changing expectations. It could also be that while the easily-fermentable sugars were consumed quickly, a less-sweet complex sugar was later broken down into a more-sweet (fructose?) sugar after the early-active parts of the culture were relatively inactive. Or maybe the remaining sugars were infermentable? Or maybe at 3 weeks my ability to taste the sweetness was inhibited by some compound that had decreased by 6 weeks? Or maybe my perception of sweetness was caused by something that wasn’t actually a sugar. There are many possibilities, and flavors are not very well understood.
This was an interesting experiment, but didn’t really result in anything interesting to drink, or to apply to a future kombucha (I combined it with other things to drink it). I was disappointed that while it looked promising at 8 weeks, nothing else really happened in the following 8 weeks. My brother has the equipment back for whatever his own experiments may be. :)