A quality Kombucha, with its flavor, color, and natural fizz, always ends up reminding us of a soft drink. It's true that the word "soft drink" makes us think of something that's not good for our health or the planet, but in the Kombucha Universe, we can create a type of natural, healthy, and more sustainable soft drink.

After choosing your flavors, we move on to the carbonation stage, better known as secondary fermentation (F2), without the presence of oxygen (anaerobic), in which we aim to "trap" the carbon dioxide produced inside the bottle so that it is incorporated into the liquid.

It's important to remember that the two steps – flavoring and carbonation – are optional, since Kombucha will already have all its qualities and benefits after the first fermentation. New flavors and natural carbonation simply open up more possibilities for enjoying a healthy drink at any time of day.

To make your process easier, we've created a Flavoring and Aromatization Kit that simplifies learning the key concepts and comes with perfect bottles for the process, as well as 3 flavoring ingredient combinations (for 1 liter of kombucha). Click here to see the kit.

Related : How to Make Kombucha at Home

What is carbonation?

What happens in this stage is the production of carbon dioxide resulting from the transformation of sugar by yeast. As you can see below, alcohol is also produced in this fermentation, so attention must be paid to how it is produced.

The second fermentation of Kombucha is done without the presence of oxygen (anaerobic) and can take place directly in the bottle.

How to Carbonate Kombucha Naturally?

This phase is called the second fermentation (F2), without the presence of oxygen (anaerobic), where the microorganisms of the Kombucha culture will work to give life to a naturally carbonated and effervescent beverage. In this phase, the predominant work is done by the yeasts, since there is no oxygen for the action of the bacteria.

The formula behind this chemical reaction is simple: yeast transforms residual sugar into alcohol and carbon dioxide gas. Fermentation occurs at room temperature and inside a properly sealed bottle.

During this time, carbon dioxide gas is produced and incorporated into the liquid. The second fermentation in the bottle is the technique most used by artisan kombucha masters and results in the best flavor of the beverage .

Key points for carbonation:

• Good Base – Ensuring that the base recipe has been properly followed, with the desired ingredients and quantities for healthy fermentation.
• Transforming Ingredient - Ensure that there is residual or additional sugar for transformation into CO2.
• The Right Bottle - It's important to use bottles that don't let the gas escape - with a mechanical cap.
• Temperature – One of the main factors accelerating the process is that the higher the temperature, the faster it will be.

Transforming Ingredient

Sugar is the transformer in this process, and temperature is the accelerator. When you taste Kombucha after F1, you should be able to feel the sugar in the drink. We divide it into two types of sugars:

Residual sugar – After harvesting, it is desirable that there is still a quantity of sugar available to be fermented by the yeasts present.

Added sugar - this occurs when ingredients containing sugar, such as fructose from sweet or dried fruits, whole juices, or pulp, are added. With added sugar, the yeast will have more nutrients to transform it into CO2 (gas).

We do not recommend adding pure sugar during the second fermentation , as Kombucha can become explosive and alcoholic, but if you wish to do so, do not exceed 5 grams of sugar per liter.

Promoting Ingredients

There are ingredients that, even without sugar, stimulate carbonation because they contribute other types of nutrients that promote fermentation .

This is the case with ginger, which contains wild yeasts, as well as pineapple, which contributes yeast and fructose. Hibiscus flower, yerba mate, and coffee also have a stimulating effect due to the presence of nitrogen, tannins, and caffeine.

Using the Right Bottle to Make Kombucha

The use of bottles that aid in natural carbonation is fundamental to this process. Often, Kombucha has all the conditions to become effervescent, but all the gas produced at this stage ends up escaping due to the use of unsuitable containers.

The most recommended bottles are those with mechanical caps, which ensure that the gas does not escape and remains entirely inside.

For those starting out in the world of Kombucha , we recommend reusing a PET bottle because it's possible to feel the pressure inside and understand the amount of gas being produced, which makes the process safer and prevents dangerous explosions.

When you feel more confident, you can switch to flip-top bottles, which have a mechanical cap that ensures the produced gas doesn't escape. You can even do both simultaneously. This way, you can know when the process will be finished.

The plastic bottle trick is simple and effective. Leave about three fingers' width of space between the liquid and the top of the bottle. Before closing, squeeze the bottle so the liquid rises and seal it tightly. Leave it at room temperature and you'll notice in a day or two that your bottle will slowly expand until it reaches a point where it's completely dilated and hard. At this point, there's no doubt that your drink is carbonated.

It is recommended to leave a small space in the bottle for gas formation before filling and proceeding to the second fermentation of the Kombucha. A maximum of two fingers' width of space is sufficient to ensure greater safety when opening the bottle. Too much space and oxygen inside the bottle is not desired for natural carbonation , as less CO2 will be incorporated into the liquid.

How to Open the Bottle Safely?

For those who have undergone a long second fermentation, it is recommended to open the bottle after a few hours in the cold, or preferably below 4°C. The cold stabilizes the action of microorganisms and reduces the agitation of gas particles. Therefore, it is much safer to open the bottles at a low temperature.

Once you know that kombucha is highly carbonated, in addition to opening it while it's cold, we also recommend opening it slowly over a sink to gauge the carbonation level. If gas is escaping from the bottle, it's best to be in a suitable environment.

Opening a bottle of highly carbonated kombucha at room temperature without opening it gradually can be dangerous or at least unpleasant, because it leaves the whole house dirty.

8. Tips for Greater Carbonation

1. Use the correct bottles, such as bottles with a mechanical cap, to prevent gas loss.
2. Reusing a PET bottle to conduct secondary fermentation tests and learn about the variables - residual sugar, temperature, and time.
3. It ensures the existence of residual or added sugar to be processed.
4. He uses ingredients that stimulate carbonation, such as ginger and pineapple.
5. Fill the bottle to the top, leaving no space so that the CO2 can be absorbed by the liquid.
6. Fermentation in a warm place (between 22 and 27°C)
7. Be patient and don't open the bottle every day to check for gas. Every time you open it, gas escapes and isn't incorporated.
8. Open it when it's cold and do it carefully to avoid accidents!

What is the ideal time for the second fermentation?

After explaining the main points, it's clear that it's not an easy answer. When we're asked about the ideal time for the second fermentation, we always have to respond with more questions like:

• How much sugar did you use in the F1 recipe?
• How long should the first fermentation take and at what temperature ?
• What ingredients were added for flavoring and in what quantities?
• What is the average temperature during the second fermentation?

Without these answers, it's impossible to give a time estimate for F2. The most important thing in this process is understanding the chemistry behind it, having an idea of ​​the ambient temperature, and knowing how much residual (or added) sugar will be present before the second fermentation.

As a result, by understanding these variables, it is possible to conduct experiments in order to acquire the necessary skills to identify the optimal secondary fermentation time for your Kombucha , by combining the variables: sugar X temperature.

The more you know about the science behind natural carbonation, the better your Kombucha will be !

Conclusion

Now that you have the tips for increased carbonation, are you ready to start brewing? If so, be sure to follow us on social media @ mai.kombucha so we can follow each other's progress in making this wonderful beverage.