Not getting carbonation can be a huge source of frustration when making kombucha. Identifying whether the issue occurs during primary or secondary fermentation is the first step in determining the root cause of the problem.
There is a often a misconception around the idea of carbonation and primary fermentation. I get countless emails asking if something is wrong with their kombucha, it isn’t fizzy at all and it has been fermenting for one, sometimes two weeks. The most important first question here is whether the problem is happening in the primary fermentation or secondary fermentation. The first question is a very important detail because you will never have carbonated kombucha after just the primary fermentation. The primary fermentation is an open-air ferment, meaning that all the carbonation produced is allowed to evaporate. Think of what happens when you leave the cap off of a soda bottle, and later you come back, and it’s flat. This is because the carbonation has gassed off and out of the liquid. Since primary fermentation is open-air, it’s impossible to get carbonated kombucha at this step. This is where the bottle conditioning comes in but first let’s cover how carbonation is made in the first place.
During fermentation, yeast consumes sugar and converts it into two byproducts – alcohol and CO2. CO2 is a gas, and when it’s inside a liquid, and when allowed, it will escape into the air, think evaporation. So when making kombucha, even if you have a big SCOBY on the top of your brew, the gas molecules are tiny and will find a way around it and into the air through the cloth cover on your kombucha brew jar. If you cap off the fermenter with lids designed to hold pressure, the CO2 then cannot escape. Once sealed, as the pressure builds, the CO2 molecules are forced to dissolve into the liquid, creating the phenomenon we know as carbonation or fizziness!
To get carbonated kombucha, after we have completed the primary fermentation, we take our finished kombucha and put it through a step called bottle conditioning. Bottle conditioning in kombucha making is often simplified and referred to as kombucha secondary fermentation; now, there is a difference between which can be found in our post covering bottle conditioning vs. secondary fermentation. So regardless of what you call it, the process is the same. You take your fermented kombucha, add some sugar, fruit, or juice and allow it to ferment again. This time, rather than fermenting in an open-air environment, allowing the CO2 to escape, we are going to place the liquid in bottles with lids designed to hold pressure. Like swing-top bottles or stout bottles, since these lids are designed to hold pressure within the bottle, the CO2 can’t escape and, in turn, is forced into the liquid creating the carbonation in your kombucha.
Sugar is a key component in kombucha secondary fermentation because it facilitates carbon dioxide production. Without sugar, there is no CO2 production and since most of the sugar you put in initially has already been eaten, it helps to add more when bottling kombucha. It’s what is referred to as “bottle conditioning” in the beer world. There will likely be some residual sugars leftover from your primary fermentation, so if you really don’t want to add any extra, you can certainly try it. But without the extra sugar, you may not have enough sugar to get carbonation or only enough sugar to get low carbonation. Just know that your miles will vary.
This is entirely up to you! I like to take this opportunity to add fresh fruit. The fruit doubles as both a source of sugar and flavor. Results will vary a bit depending on the type of fruit you use, but that’s the fun of experimenting! If you’d prefer, add a little more organic cane sugar or use honey, agave, maple syrup, etc. As long as the sugar is real sugar and not a “sweetener,” it will work for secondary fermentation. For more information on different sugars, see our post about sugar and kombucha.
When bottling your kombucha, there are two things to consider when choosing the bottles or vessel for secondary fermentation. First, are the lids designed to hold pressure? Airtight isn’t good enough; airtight lids prevent air from entering and exiting the jar but are not made to hold pressure. So as pressure builds within the bottle, at some point, it will leak. And if CO2 is allowed to escape, the carbon dioxide gas can’t build enough to carbonate. Second, will it fit in your refrigerator easily? This is just a bit of practical advice, and 16 oz bottles are usually the best size to store or take on the go.
The best two options are either flip-top bottles or stout bottles, which are the bottles store-bought kombucha often comes in. If you already have old kombucha bottles from the store, we have pressure-rated cap replacements that fit most bottles which can be found here store-bought kombucha bottle lids. For size, 16oz bottles are standard and are easily cleaned with the help of a bottle brush. Once you have the correct bottles and lids, follow our guide here on how to bottle and carbonate kombucha?
You want to keep your main brewing vessel for just that– brewing. Keeping your first and second fermentation separate creates a stable environment for your SCOBY. You don’t want to add fruit or spices to your primary fermentation as these are better suited for the next round, where the flavoring is done. It can also affect the health and balance of your culture in the long run, so you want to keep your SCOBY happy and healthy living on tea and sugar.
Don’t worry too much; carbonation can be finicky. Often temperature has much to do with it, but sometimes the yeast just don’t want to perform for you. Just keep on brewing, and it should come with time.
There are a few things you can do to try and boost your yeast population:
1. Use teas that have a high tannin content that help nourish yeast, such as our Elements Water Tea Blend.
2. Try and maintain a temperature of 75-85F to give the yeast a hand up over the bacteria.
3. Manually aerate your brew during the primary fermentation. Kombucha is an aerobic fermentation, meaning it requires oxygen. Sometimes the oxygen that it gets at the surface isn’t quite enough. You can manually provide oxygen by stirring your kombucha vigorously every few days. This often gives it the jump start it needs!
