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Secondary Fermentation (F2) Brewing Instructions

Are You Booches Ready?

Hold on to your brewing hats, booch enthusiasts! We’re diving deep into the effervescent world of secondary fermentation. We’re about to spill the tea (or should we say kombucha?) on what you need to know about this fascinating stage of brewing. So, let’s get started:

1: Make Kombucha in Primary Ferment

It might seem obvious, but the first step in the journey of kombucha secondary fermentation is, well, to make the kombucha! For a step-by-step guide on this, refer to our Primary Fermentation (F1) Tutorial.

2: Remove The Scoby & Starter Liquid for Next Batch

  • Remove Scobies: Once F1 has worked its magic and your kombucha has reached the desired level of fermentation, it’s time to remove your new scoby and the old one using clean utensils.

  • Save the New Scoby: The new scoby is your ticket to starting a fresh batch of kombucha, or you can cozy it up in a jar with some starter liquid until you’re ready to brew again.

  • Reserve Starter Liquid: Don’t forget to reserve enough starter liquid for your next batch! A good rule of thumb is to save 10% as starter liquid, but you can see exactly how much you'll need for batches of all sizes with our Starter Liquid Calculator.

  • Mind The Sediment: The sediment at the bottom is mostly yeast produced during fermentation and is generally not (much) included in your next batch, to prevent your brew from becoming overly yeasty over time.  However, it's fantastic for you F2 because yeast is what contributes to CO2 production the most.

  • Use Clean Utensils: A little tip from the pros: when interacting with your kombucha, using clean utensils and equipment is always a safer bet than clean hands.

For those aiming for brewing consistency and keen on delving into the relationship between kombucha and pH, check out more info here and give our calculator a whirl here. For a deeper dive into the importance of cleanliness in kombucha brewing, check out our comprehensive guide on the subject.

We’re just getting started on this effervescent adventure. Ready, set, brew!

3: Add Flavoring to the Kombucha

Feeling adventurous? It’s flavor time! This step is optional, but it’s your chance to let your culinary creativity shine. Whether it’s fruit juice, herbs, spices, or other imaginative flavorings – the world is your oyster! And let’s not forget our personal favorite at RBC: the Brew Booster.

  • Experiment and Enjoy: The type and amount of flavorings are all up to you and the recipe you’re following. It’s a chance to experiment and find what tickles your taste buds the most!

Remember, adding flavor is like giving your kombucha a unique personality. So, have fun with it, and who knows, you might just create a signature brew that’s the talk of the town! Keep in mind you can definitely flavor simultaneously with the next step, in your bottles.

Ready to continue the journey? Onward to the next step, booch brewers!

4: Transfer the Kombucha to a Clean, Strong, Airtight Container

Time for a change of scenery for your brew! Transfer your kombucha into a clean, robust, airtight container. This could be a glass bottle with a snug lid, a plastic container with a screw-top, or any other container capable of holding pressure. Why, you ask? If it’s not airtight, the carbon dioxide (CO2) might play escape artist, and you could end up with kombucha that’s lost its fizzy personality and flavor profile.  

  • Choose the Right Container: Ensure your chosen vessel is pressure-rated clean and free from any party-crashing contaminants that could taint the flavor or compromise the safety of your kombucha. And you certainly don't want it exploding.

  • Size Matters: Pick a container that’s roomy enough to house not just the kombucha, but also any extra guests you’ll be inviting, like fruit juice or herbs.

Once your kombucha is safely in its new home, seal that container tight! We don’t want any air gatecrashing the fermentation party. 

5: Seal the Container and Let the Magic Happen!

Alright, Booch Buddies, it's time to seal the deal! Once you’ve added your chosen flavorings, ensure the container is sealed tight. We wouldn’t want any of that precious CO2 making a break for it! Now, let your kombucha sit and ferment for an additional 1-4 days. This duration will depend on your taste buds' preference for carbonation and flavor.

  • Fermentation Fizz: During this cozy time, your kombucha will continue its fermentation journey, producing carbon dioxide and gaining that signature fizzy personality.

  • Flavor Fusion: The added flavorings will mingle and infuse into the kombucha, contributing to its final tantalizing taste.

  • Experimentation Station: The fermentation duration is your playground! Some like their booch lightly carbonated and gentle, while others enjoy a bubbly, tangy kick. Play around with different times to discover your perfect brew!

Strength Check: It’s crucial to ensure your container is a Hercules of containers! As the kombucha ferments, it’s going to build up pressure. A container not up to the task might give in, leading to a potential kombucha catastrophe! Always use a container designed for fermenting liquids and capable of handling the pressure.

Temperature Tales: A quick reminder – the warmth of your F2 environment will influence the carbonation speed. The warmer it is, the faster your brew will dance to the carbonation tune! So its important to keep your F2 brew in the same temperature range as F1, 74-84F.

So, let your kombucha work its magic, and soon you’ll be sipping on a brew that’s uniquely yours! Keep the vibe alive and enjoy the fermentation symphony! 

6: To Burp or Not to Burp, That’s the Question!

Alright, Booch Crew, let’s talk about burping – no, not that kind! We’re diving into the art of burping your bottles during secondary fermentation. This technique is all about releasing that built-up pressure inside the bottles, a byproduct of the carbon dioxide from the fermentation fiesta!

  • Why Burp? If the pressure plays the overstay game, it could lead to bottle ruptures or leaks – a definite party foul! Especially if you’re using glass, this could be a safety hazard, not to mention a sad goodbye to your precious kombucha. Bottle bombs? No, thank you!

  • How to Burp: Gently and slowly open the lid or stopper to let the CO2 make its grand exit. Be cautious! The kombucha might put on a fizzy show, so release the pressure with care to avoid any spillage or splashes.

  • Frequency Fun: How often should you burp? It’s all about experimenting! Some brewers are daily burpers, while others prefer a more relaxed schedule. Find your rhythm and keep that carbonation in check!

Benefits of Burping:

  • Controls the carbonation level, influencing taste and mouthfeel.
  • Prevents bottle mishaps – we’re looking at you, ruptures and leaks!
  • Aids in avoiding over-fermentation.
  • Enhances consistency and quality without extra gadgets.

Drawbacks of Burping:

  • Requires regular check-ins and attention.
  • Potential loss of carbonation and flavor if overdone.
  • Can get a bit messy if not handled with care.

Final Thoughts: Unless you’re rocking a pressure gauge or a carbonation tester, burping is your friend! The benefits outweigh the drawbacks, ensuring a safe and tasty brew. It might be a bit more hands-on, but trust us, avoiding bottle bombs and savoring that perfect fizz is worth the effort! Keep the booch vibes flowing and happy burping!

CO2 Solubility and Temperature

CO2 solubility in liquids, like your kombucha, is highly dependent on temperature. Here’s the science breakdown:

  • Cold Temperatures: When your liquids are chilled, CO2 finds it cozier to stay dissolved. The lower temperature causes allows more CO2 to dissolve and keeps it more stable, preventing escape.

  • Warm Temperatures: As the temperature rises, the molecular jamboree gets more energetic. The increased movement results in higher pressure, causing CO2 to want to escape from the solution. This is why a warm soda might seem flatter.

Chilling and Re-warming Stability

Now, let’s address the intriguing part – the stability of CO2 after chilling and re-warming:

  • Chilling Effect: When a beverage is chilled, CO2 dissolves more efficiently, reaching a state of equilibrium within the liquid. This process also leads to the formation of carbonic acid, which further stabilizes the CO2 in the liquid.

  • Re-warming Scenario: Once the chilled beverage is re-warmed, one might expect the CO2 to escape just as it would have before chilling. However, the CO2, having achieved a stable state during chilling, doesn’t escape as readily. The formation of carbonic acid and the achieved equilibrium contribute to this increased stability.

Practical Implications for Kombucha Brewing

  1. Before Refrigeration:

    • Overflow Risks: When your kombucha is fermenting at room temperature during the secondary fermentation (F2), it’s in a warmer state. This means CO2 is more likely to escape the liquid, leading to pressure build-up in the bottle. If the pressure becomes too high – voila, you have the risk of an overflow or even a bottle bomb!

    • Burping Necessity: This is where the practice of “burping” your bottles can be important. Regularly releasing some of the built-up pressure can prevent overflows and ensure the safety and quality of your brew.

  2. After Refrigeration:

    • Stable Fizziness: Once you’ve chilled your kombucha in the fridge, the CO2 has dissolved more efficiently and stabilized within the liquid. Even if you take it out and it warms back up, it’s less likely to overflow compared to before it was refrigerated.

    • Safer Handling: This increased stability means that you can enjoy a fizzy, flavorful kombucha with less risk of a kombucha geyser when you open it!

Brewing Tip:

  • Chill Before Opening: To minimize the risk of overflow and maximize carbonation, it’s a good practice to refrigerate your kombucha before opening it. This way, you’re harnessing the physics of CO2 solubility to make your brewing experience smoother and your kombucha even more delightful!


Understanding the interplay between temperature and CO2 stability is not just a scientific curiosity, but a practical tool for every kombucha brewer. By leveraging this knowledge, you can ensure a safer brewing process, prevent overflows, and enjoy a perfectly fizzy and flavorful kombucha every time!

7: Enjoy your brew!

You've done good young skywalkers...enjoy your brews, Booches! 

Note: These steps are a general guideline, and the specific process of kombucha secondary fermentation can vary depending on your preferences and the equipment you are using. It's important to follow the instructions for your specific recipe and to use clean, sanitized equipment to avoid contamination. It's also important to be careful when handling the kombucha during the secondary fermentation.

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