Kombucha tastes sour because its bacteria turn sugar into organic acids, mostly acetic acid, which brings finished kombucha to a pH of roughly 2.3 to 3.8 according to the Kombucha Brewers International Code of Practice.
pH measures how strong the acidity is but not which acids made it, so two kombuchas at the same pH can taste sharp or soft depending on the mix of acetic, gluconic and lactic acid.
Kombucha is sour because its bacteria make acids. Yeast breaks down the sugar in sweet tea, and acetic acid bacteria turn what the yeast makes into organic acids, acetic acid above all. That takes finished kombucha to a pH of roughly 2.3 to 3.8, the range the Kombucha Code of Practice gives. For comparison, plain brewed tea is close to neutral.
| Acid | Made by | Taste | Detectable at |
|---|---|---|---|
| Acetic | Acetic acid bacteria | Sharp, vinegar-like | 175 mg/L |
| Lactic | Lactic acid bacteria, in some cultures | Soft, rounded | 400 mg/L |
| Citric | Small amounts | Bright, citrus | 60 mg/L |
| Gluconic and glucuronic | Bacteria oxidising glucose | Mild, smooth | Not given |
What pH does and does not tell you
pH is a measure of how acidic a liquid is, and every brewer tracks it, because it tells them when a batch is close to done and whether it is safe. The KBI chemistry primer is careful about its limits: pH cannot tell one acid from another. A kombucha heavy in acetic acid tastes sharp and vinegary. One with more gluconic or lactic acid can sit at the same pH and taste softer. Which acids a batch ends up with depends on the culture, the sugar, the temperature and the time.
Acidity is also what keeps a batch safe
Fresh sweet tea is an easy home for the wrong microbes, so the first job of a brewer is to make it acidic quickly. The Code requires at least 10 percent finished kombucha as starter for food safety, and recommends a pH of 4.6 or lower once the culture is in. For the finished drink it sets a maximum of 3.8, and says it must be below 4.6. Boochy Mama's, for one, puts its own kombucha at pH 3.3.
How tea and time move it
Time is the big dial: the longer the first ferment, the more acid. Tea matters too. In a 2022 Frontiers in Microbiology study the same culture fermented black and green tea for 12 days. The black tea batch reached pH 3.69 against 4.00 for green, with more total acidity, 40.7 against 28.3 milliequivalents per liter. Good kombucha balances that acidity with some sweetness and with the tea itself, so it reads as bright rather than harsh.
Questions
What is the pH of kombucha?
Usually 2.3 to 3.8, according to the trade's Code of Practice. Boochy Mama's FAQ puts its own at 3.3.
Why is kombucha acidic?
Acetic acid bacteria in the culture turn the products of fermentation into acids, mainly acetic acid. Some cultures also make gluconic and lactic acid.
Why does starter liquid matter for safety?
Adding at least 10 percent finished kombucha drops the pH of fresh sweet tea fast, and the Code recommends a pH of 4.6 or lower once the culture is in.
Does tea type change acidity?
It can. In a 2022 study the same culture took black tea to pH 3.69 and green tea to 4.00 after 12 days.
