Starting Acids for Kombucha

As I was thinking about what to title this post, I was tempted to give it a very academic-sounding name, like “Effects of Inoculating Acids on Kombucha Flavor”, because it is clear and precise. But it seemed a bit too wordy, and since I wasn’t intending to come up with an academic title until I was struck that it sounded like one, I decided it was too much.

The basic idea is that when a new batch of kombucha is started, a portion of finished kombucha is added. The purpose of twofold: It inoculates the culture into the new raw material; and it lowers the pH of the raw material so that it is inhospitable to undesirable microbes. Since the kombucha culture itself tolerates a low-pH (high-acidity) environment rather well, this creates a situation in which the kombucha can thrive and anything else is at a severe disadvantage.

Following normal convention, this isn’t strictly necessary. In addition to adding some kombucha, it is customary to add a scoby, and the scoby itself is quite effective at colonizing the batch. As the culture from the scoby grows, it produces alcohol (which many other microbes won’t like) and then acid (which many other microbes won’t like). The risk here is that microbes foreign to the scoby will have an opportunity to take hold, and will either manage to stunt the kombucha culture’s development (which seems unlikely) or produce undesirable flavors, toxins, etc that are retained after the kombucha is done. Scoby-only inoculation is effective, but allows a greater risk of contamination early in the process.

Additionally, without doing something to prevent the growth of “wild” microbes, the results from batch to batch will be less consistent. Commercially fermented products of many varieties tend to eschew the use of a “mother” to “seed” new batches because it allows them to remove a lot of variables, increasing product consistency (often a primary goal). Using a fresh starter (probably purchased at low cost from a commercial lab) also simplifies the production process, which drives down cost (also often a primary goal).

So, with all of that background out of the way, I can finally describe my experiment to see how starting acid affects the flavor of the finished kombucha. This is a followup to my 10-month old posts on Kombucha Science and Coffee Kombucha. The latter post ended with:

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.

Although I hadn’t referred to this when I started that’s exactly what I did, mostly. I had ascorbic (and phosphoric) on-hand, but decided to use only four varieties to simplify things.

I used acids from LD Carlson, adding enough to make 1 cup of distilled water pH 3.2. This is as much kombucha as I would add to a new gallon, but each batch here was 1 quart. That’s probably going to over-emphasize the effects of the acid, which is an unfortunate mistake, but may in the end be useful if the differences would have otherwise been undetectable (to my dull palate). For an additional datapoint, my eldest daughter, who will not try my kombucha because it “smells like vinegar”, sniffed each one and ranked them in terms of vinegaryness. YMMV.

lactic acid

  • .375 tsp added
  • finished pH 3
  • ~.25″ scoby, irregular
  • unusually high number of yeast threads
  • tastes relatively normal, medium astringency, mild sweetness, medium tartness. Considering the pH, it doesn’t taste very sour.
  • Ranked second least vinegary in odor by vinegar-phobe child.

citric acid

  • .375 tsp added
  • finished pH 3
  • ~.5″ scoby, a little thinner in the middle
  • unusually high number of yeast threads
  • tastes relatively normal, medium astringency, mild to medium sweetness, mild tartness. Not at all vinegary. It has a subtle undercurrent of something, probably lemon, but I’m not sure. There’s a very slight bitterness to it.
  • Ranked most vinegary in odor by vinegar-phobe child.

malic acid

  • .25 tsp added
  • finished pH 2.8
  • ~.5″ scoby, a little thinner in the middle
  • unusually high number of yeast threads
  • tastes relatively normal, medium to high astringency, mild to medium sweetness, mild tartness. Not at all vinegary. It has a subtle undercurrent of something, probably green apple, but I’m not sure. There’s a very slight bitterness to it.
  • Ranked second most vinegary in odor by vinegar-phobe child.

tartatic acid

  • .375 tsp added
  • finished pH 3
  • ~.5″ scoby, regular (even thickness)
  • less brown yeast threads, but some slime
  • tastes relatively normal, and yet distinctly different. Medium astringency, mild sweetness, mild tartness. Not at all vinegary. This is definitely more complex than the other three. There’s a mild bitterness to it that I don’t enjoy, but I suspect it’s key to the complexity.
  • Ranked least vinegary in odor by vinegar-phobe child.

I was expecting the one with citric acid to be rather vinegary. Why? Because I had read this on Wikipedia: When citric acid is added, it is always done after primary alcohol fermentation has been completed due to the tendency of yeast to convert citric into acetic acid. It didn’t work out like that. I’m not sure why, but I suppose there could be a million different reasons.

It’s interesting that each one had an unusual amount of yeast threads or slime. Neither is a problem, but not what I normally see. Perhaps this resulted from the unusually high pH at the start of the batch. It’s also interesting that the acid affected the scoby development. Trivia: Malic was apparently the strongest acid present (least added), and also resulted in the most acidic kombucha despite having normalized the starting pH; and the two with the most vinegar odor are the two that have the most intense, quick, and brief sourness. Lactic and tartaric are less intense, take longer to build, and are sustained longer.

I’m not sure that I can apply these results in any particular way, except maybe to avoid a too-low starting pH. I’m not sure that this leads me directly into some new experiment, but having seen where this started reminds me that it’s time for another try at coffee kombucha.

Advertisements

One thought on “Starting Acids for Kombucha

  1. Pingback: Kombucha Fermented Apple Cider | :|

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s