Kombucha Carbonation Tips: How to Bottle, Flavor, & Second Ferment

Last Updated on May 16, 2023

Fizz. Pop. Bubbles. Spritz. That thing that all kombucha home brewers lust after: carbonation. Not too much though! We don’t want booch bombs on our hands. Like so many things in life, carbonation is all about that delicate balance, which can be hard to achieve. Hopefully I can help you with that! Not to toot our own horn, but we are known for some pretty fizzy brews around here…

If you are after that perfectly carbonated kombucha, look no further! Read along to learn all our tips and tricks for bottling, flavoring, and second-fermenting homemade kombucha – to achieve a deliciously bubbly finished beverage. The top 8 factors that influence carbonation are revealed!

This post is geared towards folks who already understand the basic process of brewing kombucha, including primary fermentation. If that doesn’t sound like you, check out our “How to Make Kombucha 101″ post – and then come back here after!

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The Great Quest for Carbonation

“How do I make my kombucha fizzy?”

Several factors influence how carbonated your finished kombucha will be, including the time, temperature, type of flavor added (if any), how you fill your bottles, and more!

Let’s break down all these variables, one by one.

But first, it will be helpful to understand the science about what creates carbonation in kombucha in the first place. This foundation should help clarify why the other factors are important, and how they work together to achieve our goal!

How is carbonation created?

Here is the basic science behind bubbly kombucha: When your kombucha goes through the primary fermentation stage in its main crock, it is an aerobic process. The SCOBY in your vessel is a symbiotic culture of bacteria and yeast. SCOBY culture interacts with sweet tea and air to produce beneficial bacteria (probiotics), acetic acid, and yeast. In this process, the pH drops, a lot of the sugar from the sweet tea is broken down and vastly reduced, but the kombucha isn’t yet carbonated.

In contrast, the secondary fermentation stage, also known as “second ferment”, is done in an anaerobic environment; without air. This is accomplished by bottling your finished kombucha in air-tight bottles. Most kombucha brewers like to add fruit chunks, fruit juice, or puree at this stage. The fruit added to the bottle acts as a new sugar source for the bacteria and yeast to feed on. Thus, the yeast will work to break down those sugar molecules into carbon dioxide (CO₂) and ethanol. In the absence of air, the CO₂ is trapped within the sealed bottles, and boom! Carbonation is born.

C₆H₁₂O₆ (glucose) → 2 C₂H₅OH (ethanol) + 2 CO₂ (carbon dioxide)

Note: You should never “flavor” or add fruit to your primary vessel. It is not good for the SCOBY.

8 Factors That Influence Kombucha Carbonation

1) Kombucha Bottles

If I had to pick just one factor that influences the carbonation level of kombucha the most, it would be the bottles used. Because no matter how perfectly you do everything else, if your bottles are not truly air tight, the carbon dioxide produced during secondary fermentation is going to leak out! Therefore, if you want bubbly booch, you probably will not have the best of luck by using up-cycled mason jars, leftover beverage bottles, or similar. Even with a tight screw-on lid, gasses can escape. They’re sneaky little things. Especially under pressure!

The best way to contain the carbonation in kombucha is using swing-top bottles. They’re the most air-tight. However, not all swing-top bottles are created equal! You want to get high-quality bottles that are made specifically for brewing carbonated beverages! We use these 16 ounce and 32 ounce bottles by EZ Cap. They’re sold online or in homebrew stores, and are widely used for kombucha or beer making.

IMPORTANT SAFETY NOTE

We need to address a VERY, very important safety concern in regards to bottling homemade kombucha. Here we are, talking about the ways to obtain the best carbonation possible, right? But sometimes, homemade kombucha can end up way too carbonated! We lovingly refer to these as “booch bombs”.

While it may be tempting to pick up basic swing-top bottles from places like Target, Home Goods, or the like – I strongly advise against it.  99% of the time, those are not the type of high quality bottles that are made to withstand pressure. The wrong bottles CAN AND WILL EXPLODE under excessive pressure from carbonation. Literally. Like a shotgun of glass shards.

In the middle of the night years ago, a cheapo bottle of kombucha exploded in our kitchen. It seriously sounded like someone had fired a gun in our house. The pieces of glass and sticky kombucha were all over, inside, and under everything across two entire rooms. It even ended up inside the freezer somehow! Can you imagine if we would have been in the kitchen at that moment? I don’t want to. I have heard similar horror stories from many people. Therefore, play it safe and get the right supplies.  

How to Prevent Kombucha Bombs

Booch bombs are typically created when bottled kombucha is left too long in second ferment, under too warm of conditions, with too much fruit/ juice added, or some combination thereof. One way to prevent booch bombs is to get all of those things dialed in, which we’ll discuss next. Another way is to burp your bottles to check their level of carbonation. We will talk more about good burping techniques too!

2) How the Kombucha is Bottled for Second Ferment

So your kombucha has finished primary fermentation… It is tangy and fermented to your liking, and you have your bottles ready to go! Now, it is time to get it bottled up, and if you want to, flavored and carbonated.

We use the continuous brew method, and our primary ferment vessels have spigots. This makes it very easy to pull off finished kombucha to bottle. We simply place a pitcher under the spouts and draw off about 2/3 to 3/4 of the crock, leaving the rest behind to jump start the next batch. If you use the batch method and do not have a dispenser on your crock, pull out your SCOBY, and dump most of your finished kombucha into a pitcher. For more information on the vessels we use, see our kombucha supply list.

Using a funnel, fill your bottles most of the way full with kombucha. We generally fill ours up to the point in the bottle where the sides start to curve into the neck. See the photo above and below. Then, add a couple ounces of fruit juice or puree. We’ll talk about fruit options more in a moment. We don’t typically measure amounts exactly. Over time, we’ve learned how to eyeball it.

Q: How much fruit should I add to my kombucha?

A good goal for kombucha-to-fruit ratios is about 85-90% finished kombucha and 10-15% fruit additions. For example, 1-2 ounces of fruit addition per 16 ounce bottle, or 3-4 ounces per 32 ounce bottle. If we are adding straight fruit juice, I would err on the lighter side, using around 8-10% juice. When adding whole fruit that has been pureed with a little kombucha, we may add closer to 15%, since it is less sweet and concentrated than juice.

Q: How full should I fill my kombucha bottles?

If you want good carbonation, do not fill your kombucha bottles completely full! Leave an inch or two of space in the neck. We generally leave most of the neck empty. That small amount of air in the bottle at first helps to jump start the chemical reactions that lead to carbonation. Also, that little bit of space in the neck gives the carbonation somewhere to go! C02 slowly replaces the air in the neck during second fermentation.

On the other hand, do not leave a huge amount of empty space in your bottles. This can lead to too much carbonation building up in the bottle. For example, we never fill a bottle just halfway. If we have an odd amount leftover during a bottling session, we either add it back to the main crock or simply drink it plain right then.

And now… options for fruit, flavors, and more!

3) Choice of Fruit or Other Additions

The next factor that has a significant impact on carbonation is how you flavor it, if at all. Both the type of fruit (or vegetable!) and how you add it makes a difference.

The higher the natural sugar content of the fruit or vegetable, the more carbonated the kombucha will become – and faster. For example, nicely ripe, sweet strawberries will create a more carbonated kombucha than sad under ripe strawberries. Furthermore, things like beets, mangos, and watermelon usually produce more of a fizz factor than blackberries and lemon. That is, if you were to compare those flavors side-by-side, with all other factors constant. It is possible to obtain a similar level of carbonation, no matter the fruit or vegetable added, if you tweak the time – as discussed below.

Figuring out which flavors produce the most carbonation is a bit of a guess-and-check, learn-from-experience type of thing. But you’ll get it!

Fruit isn’t the only thing you can add to kombucha! We have made killer carrot, fresh turmeric and ginger booch before! Ginger always seems to help carbonation, not to mention make the kombucha extra tasty. We’ve also infused kombucha with fresh lavender buds, basil, and other goodies from the garden. I have also heard of people using food-grade essential oils to flavor kombucha, though that isn’t something we’ve ever tried. The options are seemingly endless! I will put together a post of our top kombucha flavor combinations soon.

Sometimes we do leave kombucha completely plain, with no flavoring added at all. This produces the least carbonation. That is, unless you choose to introduce a little fresh sugar to wake up the yeast. For example, by bottling plain kombucha and adding just a pinch of organic cane sugar or a squeeze of honey to the bottle along with it. If you’re working with slightly underripe fruit or other flavoring additions that don’t have much natural sugar, a little pinch of sugar or honey could be added to increase carbonation in those situations as well.

4) How You Flavor Your Kombucha: Whole Fruit, Juice, or Puree

We have found that adding fruit juice or fruit puree to kombucha creates more carbonation than adding whole fruit chunks to your bottles. Fruit chunks also provide less infusion of their flavors. Think about it… By blending up or juicing fruit, you’re breaking it down and therefore freeing up all those sugar molecules to go party with the yeasties! When fruit is left more whole, there is less mixing and surface area for the essential chemical reactions that lead to carbonation to take place.

95% of the time, we add fruit puree to our kombucha to flavor it. Our flavor choices largely depend on what is in season, readily available locally (or from the garden!), ripe, fresh, and organic! Meaning, we make a lot of beet kombucha in the winter, strawberry, melon or stone fruit kombucha in the summer, and apple in the fall. Sometimes we use fruit juice. We don’t have a juicer, but we do “juice” our homegrown passionfruit to remove the seeds. In a pinch we use store-bought organic fruit juice, which we generally have on hand for my emergency low blood sugar needs.

How We Flavor Our Kombucha With Fruit Puree

To create a fruit puree to add to bottled kombucha, we simply blend raw, organic, seasonal fruit or veggies with a little finished kombucha from the primary ferment vessel. Or, blended with a little fruit juice. For example, chunks of beets with some fresh-squeezed orange or lemon juice. That way, it can be blended into a smooth and pourable puree, but doesn’t get watered down.

I honestly don’t measure amounts, so I’m afraid I won’t be extremely helpful there. We throw some fruit in the blender, roughly chopped, and then add in enough finished kombucha (or fruit juice) to allow it to blend freely. The Vitamix does an excellent job at creating a super smooth, creamy, uniform puree! It can also handle blending up tough raw beet like a champ.

Most of our purees end up the consistency of a thin applesauce, but thicker than pulpy juice, if that is helpful… See the example below. For that bottling session, we used 4 very small local apples, about 4-6 ounces of finished kombucha, plus a ½ teaspoon of cinnamon. This created enough to puree to flavor (4) 32-ounce bottles and (2) 16-ounce bottles.

After we add finished kombucha and a little fruit puree to our bottles in the ratios described above, we cap the bottles. If all of the fruit puree seems to be floating on top, I will gently rock and invert the bottle to better mix it.

Yes, the pureed fruit method will result in a slightly pulpy kombucha. We don’t mind it that way! Also, a little “fruit cap” (mini SCOBY with fruit bits) will form in the bottle. We generally discard this blob after we pour our bottles, feeding it to the chickens. Sometimes, we do drink it. If you prefer your kombucha more smooth and clean, you can always choose to pour the finished product through one of these nifty funnel screens to strain it before drinking! Or, use juice instead of puree.

And now, we wait….

5) Temperature

Store the bottled kombucha in a temperate location to second ferment. It is okay if they’re exposed to some ambient room light, but try to keep them out of direct sunlight. Providing steady warm conditions isn’t as essential now as it was during primary fermentation. At this stage, there really is no risk of mold. The properly fermented kombucha is nice and acidic, and will not allow the fruit that you added to mold.

Kombucha that goes through second fermentation in cooler temperatures will be less carbonated, or take longer to carbonate. In contrast, very warm conditions will create carbonation much more quickly. Therefore, you can expect your winter brews to take longer to achieve the same level of carbonation as your summer brews do in a much shorter period of time. By storing your second ferment bottles in warmer or cooler locations in your house, depending on the season, you can manipulate your carbonation level and time.

When kombucha is amply fizzy from second fermentation, move it to the refrigerator. This isn’t just to make it nice and cool to drink, though that is part of the purpose. The colder temperatures vastly reduces the fermentation activity, essentially halting it. Kombucha may continue to very slightly increase in carbonation in the fridge, but not much.

6) Time

Generally speaking, the longer duration of time that bottled kombucha sits in second fermentation, the more carbonated it will become! However, there is no cut-and-dry timeframe I can provide you. The time needed to create the ideal carbonation level is going to vary wildly depending on all the other factors we are discussing today, including the amount and type of fruit added, conditions and temperature in your house, and so on.

Some kombucha flavors may become perfectly carbonated in four or five days. Others may become insanely carbonated and nearing booch-bomb status in just two or three days. Certain flavors under cooler conditions may be able to sit in their bottles for weeks on end without getting explosive! The only way you are going to be able to tell is by giving your bottles a little burp.

7) Bottle Burping Technique

When your kombucha bottles are sitting out in second fermentation, it is important to keep an eye on them. The best way to assess their carbonation level is to lightly burp them. However, I believe some peoples less-than-ideal burping methods play a huge role in their struggles to gain good carbonation. So let’s talk about the best way to burp your booch!

Burping to check carbonation

The primary purpose of burping kombucha is to check and see how fizzy they’ve become. To do this, you want to only very slightly, hardly at all, lift the swing-top latch and lid. See the video below! Are they hissing? Does the kombucha start to lift and churn? Can you feel pressure pushing back against the lid as you gently start to lift it? Burping does NOT mean fully opening your bottles. By doing so, all of the built up carbonation will easily escape and be lost!

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A post shared by Deanna ~ Homestead and Chill © (@deannacat3) on Dec 28, 2017 at 3:24pm PST

We typically start lightly burping bottles after 2 to 3 days of being in second ferment. If there is no sign of activity at all, I don’t bother burping again for several days to a week. If there is a slight fizz to it, I let them sit another few days and then move them into the refrigerator. Often times, I do not re-burp. Burping too much leads to less carbonated kombucha. After that initial check, I usually can gauge the activity of that batch and know when it is best to halt the second fermentation process by moving them into the fridge – whether it is the next day, or a few days later.

Unless it is insanely fizzy, I never move the bottles in the fridge immediately after burping. By allowing it to sit out another day or two after burping, it allows the kombucha to regain that little bit of carbonation that was lost. I can’t tell you how many times people have messaged me saying “I burped my bottles and they seemed really fizzy, so I moved them into the fridge. Then they were flat when I opened them again later!” I think they either opened the bottles all the way, or moved them into the fridge too soon, or both.

With time, experience, and playing with various flavor combos, you’ll get into your own groove and be able to better gauge your brews time and burping needs.

Burping to release excess carbonation

Another way burping can be used is to slowly release pressure from a frisky batch of booch. If you start to burp a bottle and it’s apparent that it is past “ready to go” and excessively carbonated, do not fully open the bottle! It will spew like a volcano, or worse. Lightly open the bottle a tad, but keep pressure on the lid so you can quickly clamp it shut again. Let it hiss and rise until it’s about to come out, then close it up again. Let it settle a few minutes, then repeat. You can continue this process as much as needed until it is safe to open.  

Or, here is another way to detonate a kombucha bomb. See the video below. I suggest to do this outside. Especially if beet is involved! Side note: do you think Google is going to red-flag me for using the word “bomb” several times in this post?!? 😳

8) Strength of Primary Ferment Booch

You know the saying “quality in, quality out?”. Well, the same applies to kombucha! The carbonation level of your finished second ferment is going to also depend on the strength, maturity, style, and condition of your primary ferment. Not to say that some primary ferments are necessarily more “quality”, than others… but there are certainly some factors that will contribute to a more or less carbonated booch.

Type of Tea Used

Tried and true, it has been well-documented by home-brewers that using black tea produces the most active SCOBY, and most carbonated finished kombucha.  That isn’t to say you need to use black tea alone! We always use half black tea and half green tea; a combination of organic loose-leaf black breakfast blend tea, and either jasmine green or gunpowder green tea.

For a short time we switched to only green tea, and did see a little drop in our carbonation level. I do know many brewers that get great carbonation with green, white, oolong, or other teas as well! The bottles may simply need to sit out a little longer, or, they may turn out just slightly less fizzy than they otherwise could. If you prefer other tea types, no big deal!

Time of Bottling

Ideally, you want to bottle your kombucha when it is nice and fermented, but still pleasantly balanced. Experts say that properly fermented kombucha has a pH between 2.5 and 3.5. Here are some pH test strips if you want to get scientific about it! If you do a taste-test from the primary ferment vessel, it should should taste tart and vinegary but slightly sweet still at the time of bottling.

If kombucha is bottled too early, when it is still quite sweet, there is less of an established population of beneficial bacteria and yeast within it. Not only is this less healthy for you to consume, but it will probably also be less carbonated. The friends are taken from their mother SCOBY before they’re strong and multiplied enough to do the job well.

On the other hand, if kombucha is allowed to over-ferment in to very acidic kombucha vinegar, it will sort of be past the point of return. For example, kombucha that has gone for months in primary ferment. There are some great uses for kombucha vinegar however! I will write a post on this soon.

Style of Brew

I suspect that the continuous brew method can more easily produce highly carbonated kombucha. The reason is this: when you do continuous brew, the vessel and liquid isn’t disturbed or “turned over” nearly as much as the batch method. More active starter liquid is left behind after each bottling session, resulting in faster-fermenting booch. Additionally, a layer of yeast commonly forms on the bottom of the primary ferment vessel.

Yeast are key players in converting sugar into C02 and ethanol. Thus, a more yeasty booch from continuous brewing leads to more fizz. I notice that after we do a deep clean of our crocks, which removes built up yeast, the subsequent few batches of kombucha are less quickly and less vigorously carbonated than the previous few.

There they are! The 8 factors that will ultimately influence the carbonation level of your kombucha. Put all these things together, and that perfect fizzy lifting drink is just around the corner!

Scenes from bottling day…

One last tip I have for you is this:

When you are about to pour a bottle of fizzy booch, have your glasses there and waiting. Pop the bottle, and gently pour it right away. If you pop it open and let it sit there, it can very easily rise and overflow. But pouring it right away stops that, and captures the carbonation in your glass – right where you want it.

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A post shared by Deanna ~ Homestead and Chill © (@deannacat3) on Mar 3, 2018 at 5:23pm PST

Now you can get to brewing, bottling, and flavoring your booch! See our list of favorite seasonal kombucha flavor combinations here. I hope you enjoyed this post and find it helpful in your brewing adventures, and helps you achieve that perfect kombucha carbonation. Please feel free to ask questions, leave a comment, and spread the love by passing it on! Thank you for reading.

Cheers!