This summer I lost two producers from my lineup, for almost totally opposite reasons: Yo Booch from Munich, because they'd rather not keep shipping their unpasteurized kombuchas over long distances, and Bouche from Berlin, because they've started pasteurizing theirs. This development kept me preoccupied for a while — partly because both decisions have a big impact on my little business, but also because this topic is just so interesting and important in the kombucha world.
In this line of work, a lot comes down to how you keep kombucha stable. And the answer to that sometimes tells you more about a bottle than its own label does. Let's walk through it one step at a time …
Why is kombucha "unstable" at all?
Kombucha is a fermented product: a sweetened tea gets a living culture of bacteria and yeast added to it — the so-called SCOBY (Symbiotic Culture Of Bacteria and Yeast). Over several days, these convert the sugar into acids, carbonation, and a small amount of alcohol (the alcohol content in most kombuchas is very low: commercial products are usually kept under 0.5% vol).
The lovely, and also annoying, thing about this is that the culture doesn't simply stop working once the kombucha is bottled. As long as there's yeast in there, it keeps nibbling at the leftover sugar, generating carbonation (aka pressure), as well as a little alcohol. Cold slows all of this down dramatically; warmth speeds it back up. A bottle of live kombucha isn't a finished product the moment it's filled — it's more like a state that keeps changing, whereas a pasteurized bottle is basically frozen in place at the moment of filling and just stays that way.
With my own home-brew, the first fermentation takes sometimes six days, sometimes ten, depending on how warm my kitchen happens to be. You can see it in the culture directly: in summer it's a completely different beast than in winter, building up much more pressure during the second fermentation in the thinner, swing-top bottle.
The three main "paths"
Roughly speaking, there are three ways to deal with all this "aliveness":
Pasteurizing. The kombucha is heated, killing off the culture. After that, nothing further happens: no pressure, no secondary fermentation — the kombucha is as shelf-stable as a soda. That's convenient for shipping and completely understandable as a business decision; it's just that the live cultures are gone too, and for me that's kind of the whole point. So I deliberately don't carry pasteurized kombucha.
Filtering by degrees. Unpasteurized doesn't necessarily mean unfiltered, because there's a middle path: the yeast (or part of it) gets filtered out while the bacterial cultures stay in. Gently filtering out some of the yeast is typical, and in my mind it can still be considered "raw." It makes the secondary fermentation run much more slowly, the pressure stays moderate, and the product gets more stable — and thanks to the bacteria, it stays alive.
There are several grades of filtering, though: the coarser the filter, the more yeast stays intact (and the "rawer" the product); the finer the filtering, the more yeast gets pulled out. As a rough rule of thumb, the KBI (Kombucha Brewers International, a US industry association) names a threshold of around 0.45 µm: filter finer than 0.45 µm and you also remove the bacteria, thus the product has to be labeled "sterile filtered." More coarsely filtered products, on the other hand, still count as alive. But this is just an industry guideline from the US, not German or EU law, so German producers aren't bound by it.
Some people say that filtering out too much yeast takes away from the kombucha's character. I'm honestly still learning here myself, so I haven't formed a concrete opinion on this yet. For now, I consider lightly filtered kombucha fine for my Kombude lineup, as long as the product stays "alive" and unpasteurized.
Do nothing at all. Fully raw: bacteria and yeast both stay completely in, and the culture keeps developing whenever the bottles aren't chilled. This is the most "alive" kombucha, usually the most complex in taste, and at the same time the most demanding when it comes to storage logistics and shipping.
Why high summer is crucial
Right in the middle of a heatwave in deep summer is when things gets tricky. If you ship a fully raw, or only very lightly filtered, bottle across the country in July — in a package that might spend a whole afternoon sitting in the blazing sun on a delivery truck — the heat speeds up exactly the processes from before: more pressure, faster fermentation. In extreme cases bottles can leak or even burst, or the alcohol content slowly climbs. Above 1.2% vol, EU labeling law (LMIV) kicks in: at that point the alcohol content officially has to go on the label.
Considerations like these are what ultimately led Yo Booch to stop supplying to Kombude: shipping their raw product in summer got too risky for them. On top of that, they'd already run into repeated problems with long-distance shipping (lost packages, broken glass bottles, etc). That was very sad news for me because I genuinely loved their kombuchas. But I completely understand their decision and I think it's really important that they stayed true to their principles. From my end the door is always open in case they change their mind down the road.
It's also the reason there's a "cold chain" — e.g. refrigeration & tight shipping windows — behind every Kombude delivery. And in the hottest part of summer I'd rather not ship at all, and take a few weeks of vacation instead :). It's the same reason I don't plan to deliver outside of Germany for the foreseeable future.
Bouche at the other end of the spectrum
How much yeast individual producers extract (i.e. how coarsely or finely they filter), if they filter at all, differs from brand to brand. In practice almost nobody gets by with no filtering, except for maybe home-brewers or makers like Yo Booch who rarely, if ever, ship long distances.
For a while Bouche was the robust middle ground in my lineup: their kombuchas were unpasteurized but strongly stabilized, since they'd largely spun out the yeast in a centrifuge. Their Kombuchas were less sensitive than a raw product, but for me they still belonged in the fridge. With the switch to pasteurizing, though, the product has changed categories: it's now fully shelf-stable (even for shipping abroad), but no longer alive. For a lineup like mine with a firm red line — "unpasteurized" — that sadly means Bouche falls out of it. I wish Bouche all the very best and I still find their kombuchas delicious and their aesthetic beautiful, but they just don't fit anymore with what I want for the Kombude.
What this means for you
In practical terms, it comes down to one thing: unpasteurized kombucha belongs in the fridge. Kept cool, the culture stays calm, pressure stays in check, and the flavor is exactly as it should be: more alive and more layered than a heated bottle. It's no big deal if the kombucha spends a few days out of the fridge, e.g. while being shipped, but fundamentally it isn't a drink for the kitchen pantry. It's rather something you put in the fridge as soon as you can after it arrives, and enjoy cold.
This same aliveness is one of the reasons unpasteurized craft kombucha is very special, and why the whole cold chain logistics behind it is delicate, expensive, and truly not for the faint of heart!
-
Thanks for reading! If you'd like to browse the Kombude lineup, Mix & Match is the perfect way to navigate through our Shop.