# The acidity and alcohol numbers, from a university

> Colorado State University's food safety fact sheet gives the pH window, the alcohol figures and the contamination risks, with 34 references behind them.

Topic: Safety
Read it before deciding a batch is fine, and before repeating any figure about kombucha to someone else.

## The source under review

- Article: Food Source Information: Kombucha
- Published by: Colorado State University
- Written by: Laura Bauer
- Kind of source: University
- URL: https://www.chhs.colostate.edu/fsi/food-articles/complex-food/kombucha/
- Last checked by Kombrewcha: 2026-09-17

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Almost everything written about kombucha safety online is written by someone who sells kombucha,
teaches kombucha, or drinks a lot of it. This fact sheet is not. It is published by Colorado State
University's College of Health and Human Sciences as part of its Food Source Information series,
it is externally reviewed, and it carries 34 references.

That makes it the page to check a number against.

## The figures worth having

**Acidity.** The safe window is below pH 4.2 and not below about 2.5. A brew should drop from
roughly pH 5 to 4.2 within the first seven days. That first week matters: a batch that has not
acidified is a batch with nothing defending it.

**Alcohol.** Fermentation produces alcohol. Commercial drinks must stay under 0.5% by volume to be
sold as non-alcoholic, and the fact sheet notes that alcohol can continue to rise after packaging.
A home brew left long is not held to that limit and can carry more. Anyone who says home-brewed
kombucha is always under 0.5% is stating something the source does not support.

**Contamination.** The named risks are wild yeasts, stray bacteria, fruit flies, and *Aspergillus*,
a mold. The controls are sanitary equipment and a tight cloth cover. The fact sheet specifically
advises against cheesecloth, whose weave lets flies through.

**Mold.** A culture showing mold is discarded and the equipment is sanitized. It is not rinsed. It
is not scraped. It is not saved for starter.

## Who it says should be careful

The fact sheet notes FDA guidance of up to about four ounces a day for most people, and lists
groups for whom kombucha is not advised: people who are immunocompromised, pregnant or lactating,
and young children. It also records the two 1995 Iowa illness cases honestly: investigated by the
FDA and CDC, with no causal link established, and no confirmed outbreak since.

That last point is worth stating plainly, because the internet tells it both ways. The record
does not show kombucha causing an outbreak. It also does not show that home brewing carries no
risk. Both things are true.

## What to bring back to a brew

Check acidity rather than assuming it. A pH meter or strips cost little against the alternative of
guessing, and the fact sheet recommends monitoring during fermentation rather than at the end.

Treat the first week as the one that matters. If a batch has not turned acidic in seven days, that
is the signal to look at temperature and starter liquid, not to wait longer and hope.

## Worth knowing about the source

This is an institutional summary, not a brewing guide. It will not help with flavor, carbonation
or what a healthy culture looks like on day four. For that, read a practitioner. What it will do
is settle a number, and it is the right source to cite when one is in dispute.

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This is a review by Kombrewcha of a third-party article. Kombrewcha is not affiliated with Colorado State University. Read the original at https://www.chhs.colostate.edu/fsi/food-articles/complex-food/kombucha/.