All four contain some alcohol, because the yeasts that make them fizzy turn sugar into ethanol. When Australian food regulators
tested 239 shop-bought fermented drinks, about two-thirds of the kombuchas and nearly three-quarters of the water kefirs had more than
0.5% alcohol by volume. More than a fifth of the kombuchas and more than a third of the water kefirs were above 1.15%. Every milk kefir
tested was under 0.5% (FSANZ, 2019). Homemade drinks have been measured far less often. The figures range from trace
amounts in a tested kombucha recipe to about 2.6% in a lab-made water kefir based on a household recipe. That is close to a light
beer.
So it depends on the drink, the recipe and above all on how long and how warm it ferments. Below are the measured numbers, what
makes them rise, and who should skip these drinks.
What Lab Tests of Shop-Bought Drinks Found
Several studies have tested fermented drinks sold in shops. The largest is the coordinated survey by Australian food regulators,
which sampled 239 drinks in five states in 2017 and 2018: 132 kombuchas, 43 water kefirs, 7 milk kefirs and 57 others, including
ginger beer (FSANZ, 2019). A study in British Columbia compared 107 kombuchas collected by the province’s Centre for
Disease Control with 31 water kefirs (Situm et al., 2020). New Zealand researchers tested nine kombuchas
(Nordstrom et al., 2026), and a Brazilian study tested 30 kombucha brands, all labelled as having up to 0.5% alcohol
(da Silva and Botelho, 2025).
| Drink | Australian survey: share of samples by alcohol | Other tests |
|---|---|---|
| Kombucha | 35.2% under 0.5%; 41.9% from 0.5 to 1.15%; 22.9% above 1.15% | 53% of 107 samples above 1% in British Columbia; 22% of nine samples above 1.15% in New Zealand; 60% of 30 brands above 0.5% in Brazil, with 0.10% to 1.70% |
| Water kefir | 26.7% under 0.5%; 36.7% from 0.5 to 1.15%; 36.7% above 1.15% | 19% of 31 samples above 1% in British Columbia; eight market samples tested in a British Columbia lab measured 0.14% to 1.70% (Sy et al., 2023) |
| Milk kefir | All 7 samples under 0.5% | None |
| Ginger beer and other fermented soft drinks | 68.6% under 0.5%; 21.6% from 0.5 to 1.15%; 9.8% above 1.15% | NSW Health puts ginger beer and kvass together at about 31% above 0.5% (NSW Health) |
Sources: FSANZ, 2019; Situm et al., 2020; Nordstrom et al., 2026;
da Silva and Botelho, 2025; Sy et al., 2023; NSW Health.
These were commercial drinks, made by businesses that are required to keep alcohol under control and label it. Even so, the
Australian survey found that the alcohol in some kombucha and water kefir samples rose during their shelf life, and that the way a
drink was made fizzy and the fruit or flavourings added to it affected how much alcohol it had (FSANZ, 2019). In the
New Zealand study, brewers’ own accounts pointed the same way: lots of sugar at the start, flavourings added after fermentation, little
checking of pH and temperature, and testing tools that weren’t precise (Nordstrom et al., 2026).
Homemade Kombucha, Kefir, Ginger Beer and Kvass: The Few Measured Figures
Nobody has surveyed home brews. A few recipes have been measured, though.
- Kombucha made to the University of Georgia’s tested recipe and fermented for the recommended 7 to 10 days may have trace amounts
of alcohol, under 0.016% by volume. Longer fermentation produces more (UGA Extension). Our
kombucha brewing guide gives 7 to 14 days; stop at 7 to 10 if you want to keep the alcohol down. - In a lab study, water kefir made to the proportions of a common household recipe (15 g of grains and 6 g of unrefined cane sugar
per 85 ml of water and fig extract, about 70 g of sugar per litre) and kept at 21°C under a water lock went from 1.1 to 20.3 g of
ethanol per litre in 72 hours
(Laureys and De Vuyst, 2014). That is about 2.6% alcohol by volume, the figure our
water kefir guide quotes. - A review of kefir’s composition gives a typical figure of about 0.48% alcohol for milk kefir, though elsewhere it quotes 0.5% to
2%. Grain quantity matters: in
goat’s milk kefir fermented to pH 4.5, 1% grains gave about 0.3% alcohol and 5% grains about 1% (Farag et al., 2020).
If you make milk kefir at home and want less alcohol, use fewer grains. - Ginger beer brewed with a ginger bug had more ethanol after 14 days of fermentation than after shorter times, in a study that
also found it tasted better (Oliveira et al., 2024). The abstract gives no percentage, and we found no other
measured figure for a home recipe. Our Caribbean ginger beer spends 1 to 3 days in the bottle before it goes into
the fridge, far shorter than that. - We found no published measurement of homemade kvass. Like ginger beer, it is yeast-fermented and gets more
alcoholic the longer it goes.
One likely reason for the gap between kombucha’s trace figure and the shop surveys is what happens after bottling. In the open
jar, only the surface gets oxygen, and acetic acid bacteria there use it to make kombucha’s acids. After bottling, the oxygen runs out: in a study of microbes taken from
kombucha, the oxygen in the bottle’s headspace was used up within 3 to 6 hours when acetic acid bacteria were present, and the lack of
oxygen pushed the yeasts to make more ethanol (Tran et al., 2022). Bottling with fruit or sugar for fizz is one of the steps the surveys linked to higher alcohol.
Time, Warmth, Sugar and a Sealed Bottle Raise the Alcohol
Time comes first. UGA says plainly that longer fermentation gives more alcohol, and its tested recipe stops at 10 days
(UGA Extension). The water kefir above made most of its alcohol in the first 72 hours
(Laureys and De Vuyst, 2014).
Warmth speeds it up. When water kefir was fermented at 17, 21, 25 and 29°C, ethanol was produced about 2.4 times faster for each
10°C rise (Laureys et al., 2022). At that rate, water kefir that takes three days to reach a given alcohol
level at 20°C gets there in about a day and a half at 28°C, so shorten the time in summer.
Sugar and a closed bottle do the rest. Anything sweet added at bottling (juice, fruit, more sugar) is food for the yeasts, and the
sealed bottle cuts off the oxygen that kept alcohol in check. The same yeasts make carbon dioxide, so a sealed bottle with extra sugar
builds pressure, and one left warm too long can burst. Use bottles made for carbonated drinks, not decorative bottles or jars, and chill
them before opening. Our page on
kombucha second fermentation explains how to keep the second stage short, burp or check the bottles, and get
them into the fridge. UGA advises refrigerating kombucha at 40°F (4°C) or below to slow fermentation down, and drinking flavoured
kombucha within 2 days (UGA Extension).
There is no reliable way to measure alcohol this low at home, and the professional brewers in the New Zealand study had trouble
with imprecise tools (Nordstrom et al., 2026). Assume every homemade batch contains some alcohol, and more if it
fermented long, warm or sealed with extra sugar.
Where the Legal Lines Fall
These rules are for drinks that are sold. Still, they show where a soft drink ends and an alcoholic one begins.
- US federal alcohol rules cover any kombucha at 0.5% alcohol by volume or more “at any time during production, when bottled, or at
any time after bottling”. That includes one that was under 0.5% when bottled and rose afterwards (TTB). - In Australia and New Zealand, a drink with more than 0.5% alcohol must state its alcohol content and the approximate number of
standard drinks on the label (FSANZ, 2019). In New South Wales, a drink above 1.15% counts as an alcoholic drink
(NSW Health). - In British Columbia, the liquor law’s line is 1% (Situm et al., 2020).
Under all three of those lines, a homemade water kefir at 2.6% would be an alcoholic drink, and a long-fermented, bottle-conditioned
kombucha could easily be one too.
Who Should Skip Them: Children, Pregnancy, Driving and Medicines
NSW Health names the groups most affected: children, women who are pregnant or breastfeeding, people with certain medical
conditions or on prescription medicines, and anyone who intends to drive, since fermented drinks may raise blood alcohol. Its
summary also names people operating machinery. It repeats
Australia’s national advice that not drinking alcohol is the safest option for women who are pregnant or breastfeeding and for anyone
under 18 (NSW Health). UGA adds that kombucha may not suit people with weakened immune systems, pregnant women or children
(UGA Extension). And if you avoid alcohol completely, whether in recovery from alcohol dependence, for religious reasons
or for any other reason, don’t treat a homemade fermented drink as alcohol-free: as the figures above show, one measured water kefir reached
the strength of a light beer.
The amounts are small, but they add up. An Australian standard drink is about 10 g of alcohol (healthdirect).
By our arithmetic, a 350 ml bottle at 1.15% holds about 3.2 g, so about three bottles make one standard drink. A homemade water kefir
at 2.6% holds about 7.2 g per 350 ml bottle, so fewer than one and a half bottles make one. After a standard drink it takes about one
to three hours to get back to zero blood alcohol (NSW Health).
What About Methanol?
Methanol is the toxic alcohol behind poisoning outbreaks, and it worries some home brewers. It forms when pectin, found mainly in
fruit, is broken down, which is why it is measured in apple wines and ciders (Convertini et al., 2022). The bases of
these drinks (tea, sugar water, ginger, bread) are not fruit, but water kefir is often made with figs, and second fermentations add
fruit or juice. We found no study measuring methanol in homemade kombucha, kefir, ginger beer or kvass. The outbreaks that health
agencies warn about come from unregistered alcohol, which includes informal and homemade alcoholic products and drinks adulterated with
substitute alcohols; in 2025, adulterated drinks caused 16 confirmed poisonings in Brazil (PAHO/WHO, 2025). Never distil a home
ferment, and get medical help at once if someone has nausea, headache or blurred vision after drinking alcohol of unknown origin.