Citizen Scientists Rate UK Kombucha
Building on an earlier round of experiments, UK fermentation experts Jo Webster and Caroline Gilmartin extended the range of commercial kombucha brands they tested from 12 to 16.
Jo and Caroline conducted a rigorous “citizen science” experiment to determine if they could make a fresh batch of kombucha from any of 16 commercially produced brands. The basic idea is that if the sample could grow a new SCOBY and make something that tasted OK when fed sweet tea, it must therefore contain the components of … traditionally made kombucha! They also included their home brews for comparison.
The experiment was “blinded”. They prepared the Kilner jars with sweet tea. Then, a third-party allocated each brand to the alphabetically labeled jars. Initial and follow-up taste testing, pH assessment and SCOBY measurements were also conducted blinded.

The experiment ran for four weeks, from early November to December 5, 2024. In addition to their home-brewed kombucha, the brands tested were:
- Booyah
- Fix8
- Go Kombucha
- Hip Pop
- Holos Kombucha Soda
- Holos Organic
- L.A. Brewery
- M&S
- Nania’s Vineyard
- Old Tree Brewery
- One Living Sugar-Free
- One Living Organic
- Plants by Deliciously Ella
- Pret a Manager
- Wild Alchemy
- Zak’s Kombucha
They sent a questionnaire to each company asking about production processes, alcohol/sugar content testing, their policy on making statements about health benefits, reasons for using cans or bottles, and what challenges they face as producers. They did not hear back from some companies, but most chose to respond. The pair appreciated the companies who were happy to be transparent about their process.
Kombucha categories
After running the experiment, they determined that, apart from the home brews, there were six different categories of commercial kombucha. Find out what these categories are over on their Substack account. The main problem from Caroline and Jo’s perspective is that the distinctions between these different categories of kombucha (made using different techniques) are not made apparent to consumers.
Challenges of commercial production
They acknowledge the many challenges commercial producers face, including alcohol levels and carbon dioxide build up and their experiment confirmed that producers are dealing with these issues in very different ways.
Transparency and consumer choice
Given the variety of production techniques, brands choose to emphasize different features: authentic, shelf-stable, sugar-free, adaptogenic, etc. However, the consumer is often in the dark about precisely what they are drinking. As Jo once remarked, “You can actually put drain water in a bottle and sell it as kombucha because there are no standards.” Kombucha is not a defined term.
In response, these citizen scientists have an overriding motivation:
The main motivation for us is to increase transparency around what’s on the market. This is going to involve producers being prepared to stand behind the production decisions that they’ve made and making their production interventions (or lack of them) clear to their customers.
Alcohol levels
The amount of alcohol in kombucha is of critical importance. They note that traditionally brewed kombucha is more likely to put consumers at risk by not declaring the ABV on the label.
Clarity around alcohol content is important. Someone who is pregnant might not want to have any alcohol at all. Also, if you are in recovery or if you’re avoiding alcohol, it’s really important to know that there isn’t any alcohol in there. If producers can get that sorted so that you’ve got some kind of regular way of checking your alcohol content, then I think for consumers, that would be a really good way forward. It is possible, in traditional method brewers, that the alcohol levels actually exceed 1.2 % by the time the kombucha arrives at the lips of the consumer.
[According to UK law, a drink with 1.2% ABV or less is considered “low alcohol” and does not require alcohol content to be displayed on the label.]
Results
As they reported in their Dec 5th Instagram video:
The five that had the most significant SCOBY growth were, in order, Zak’s, Old Tree Brewery, Holos Kombucha, and Jo and Caroline’s home-brewed kombucha. The one that we liked most (at the end of a month in a Kilner jar) unanimously, was Old Tree Brewery, and those that didn’t grow anything to speak of (Plants by Deliciously Ella, Fix8, Booyah, One Living Sugar-Free, and Holos Kombucha Soda). All of the others grew SCOBYs to some extent.
A 50-minute detailed description of the experiment with a full set of results is available on Jo’s Substack to anyone who wishes to subscribe for the low, low annual fee of £20 ($25). If you consume any of the brands studied or are curious to learn more about kombucha in general, you can be fully informed for the price you’d pay for just five bottles in the shops!Your subscription also gets you access to the two videos associated with the earlier experiments that I posted about here and here.

Disclaimer
The views and opinions expressed in this guest posting are solely those of the original authors. These views and opinions do not necessarily represent those of this publication.
Jo and Caroline have posted pictures of the SCOBY formation of the brands they tested at days 7, 14, 21 and 28 of the experiment. They also summarize the tasting notes and suitability of the brand as a starter for home brew.