I made a batch of kombucha where the sucrose was replaced with glucose. I used priming sugar from my local homebrew supplier, but you could also use corn-sugar or dextrose. This was a followup to my agave kombucha and brown rice kombucha, in which I try to confirm that glucose is exclusively (or at least mostly) converted into gluconic acid.
I sampled it at 14, 21, and 28 days before finally bottling it. At this point it tasted sour, and was highly astringent, but not vinegary. The pH was 3.0.
But what how does gluconic acid taste? One source describes it as having a “mild, soft, refreshing taste”. Another describes it as “mild and herbal”, while another as mild and unobtrusive. There’s probably a reason “mild” gets mentioned every time. One test found that at pH 4.0, the sourness of gluconic acid is rated 0 (out of 6), while acetic acid was rated 3. By pH 3.25, gluconic acid was rated 3, while acetic was rated 6. In other words, the pH has to get really low (for a beverage) before gluconic acid will make it taste sour.
I didn’t know this when it was fermenting, but if I had, I think I could have made a batch that tasted better. My hypothesis is that since i allowed it to ferment long enough that it tasted sour, and the sour taste is subtle, I allowed most of the sugar to ferment out. Thus, it tastes vaguely “hollow”, resembling the half-sugar kombucha. I ended up blending it with sweeter kombucha for drinking.
I attempted to confirm that glucose is gets converted into gluconic acid when making kombucha, and I have to declare this a complete success.
As an aside, here are some other things I learned about the flavor characteristics of gluconic acid.
- It is used as a “debitterant” in artificial sweeteners and diet beverages.
- Reducing bitterness seems like it would usually be a good thing, but might be counterproductive in Kombucha flavored with hops, and might cause unexpected shifts in the flavors of some ingredients (grapefruit, juniper, etc)
- Someone received a patent for using gluconic acid to can bacon (in 1953!). it states that Gluconic acid is the only acid that can reach a suitable pH without impairing the flavor. In particular, they note that “during the frying of the bacon, [gluconic acid] reverts to glucono-delta-lactone which has a slightly sweetish flavor and no acid characteristics”