Everything You Need To Know About The Second Ferment

When people refer to the second ferment while brewing kombucha they are usually referring to the flavoring and carbonation that occurs in the bottle.

It’s the part of the brewing process where we get to control the flavoring and levels of fizz. Similar to the primary ferment, there’s an art and science to it. There are plenty of ways to go wrong, and plenty of tips and tricks along the way.

By the end of this article, I hope you feel confident in your ability to control the carbonation and come up with different flavoring ideas on your own.

How The Second Ferment Works

There is a constant dance occurring at all times within the kombucha. It’s the balance between the yeast and the healthy bacteria. When the yeast’s oxygen supply is cut off it begins to produce carbon dioxide and alcohol. Otherwise known as fermentation.

The healthy bacteria feed on the alcohol to produce the acids that give the kombucha its unique flavor profile.

This is exactly what happens when you seal up the kombucha inside your bottles.

You are both cutting off the oxygen supply – forcing the yeast into fermentation – as well as sealing any carbon dioxide that builds up over time.

Once you understand this basic concept, it becomes easier to control both the flavor and the carbonation levels of your kombucha. Basically, if you want more carbonation, you want to promote the yeast side of the equation (the same applies for more alcohol.) We’ll get into how to do this below.

This is also why your primary brew doesn’t have the same flavor or carbonation level as your bottled kombucha!

Why You Should Use A Second Ferment

There are 4 reason why you should be doing a second ferment:

  1. More nutritious kombucha
  2. Lots more carbonation
  3. More control over flavor
  4. Extra alcohol

The organic acids in kombucha can take a while to develop. So if you are immediately consuming the kombucha after 7 days of primary brewing you are missing out on some additional nutrition.

Some studies have shown that it takes at least 14 days for these acids to develop. These acids include:

  • Glucuronic
  • Acetic
  • Lactic
  • Butyric

As well as countless others. Glucuronic acid deserves special attention in particular. It’s one of the most valuable and healthy components of kombucha. It’s produced by the liver and exhibits detoxifying effects that allows toxins to be excreted by our kidneys more easily.

The best way to get a really fizzy kombucha is by improving your second ferment. I cover this in detail below.

In addition to the healthy acids and extra fizz, the secondary ferment is where you have the most control over the end flavor. This is when you add ginger, fruit, cinnamon, beer hops, or any other crazy flavoring you can think of.

Finally, the second ferment also gives you a lot of control over the final alcohol levels of your kombucha (for better or for worse.)

Sounds interesting, doesn’t it? Let’s find out how it’s done!

How To Complete Your Second Ferment

The second ferment is not difficult. Once you have the basic steps down you will be well on your way to complete kombucha control. The first step is to gather all the required equipment. Here’s what you’ll need:

  • Enough bottles to hold all the kombucha with some left over for starter liquid. Don’t know which bottles to use? Check out my post here. 
  • Large funnel
  • Any flavoring agent you would like to use

Once you have everything organized and ready to go, it’s actually very simple. For these instructions I’m assuming you are using the batch brewing method. However, the concept is the exact same using continuous brewing.

1. Remove The SCOBY From The Vessel

The first step is to remove the SCOBY from your brewing vessel. This just gets it out of the way. This would also be the perfect time to separate the child from the mother SCOBY and place it in your SCOBY hotel.

If you don’t have a SCOBY hotel, just place the SCOBY in a clean bowl and cover it with a cloth to prevent contamination.

2. Add The Flavoring Agent Into The Bottle

Add whichever flavoring agent you are using (fruit juice, ginger, cinnamon, beer hops, etc.) I like to add my flavoring agent before I pour my kombucha so I can have complete control of the amount of flavoring agent as well as the space left over in the end.

3. Pour Your Kombucha Into The Bottles

Do NOT strain your kombucha before pouring it into the bottles. You need this extra yeast power to get the strong carbonation and to further develop the flavor inside the bottle.

It can be difficult to pour the kombucha into the bottles without making a mess.

The bigger the funnel, the easier it’s going to be. I also like to transfer the kombucha from the vessel into a juice jug that has a handle (something like this.) It makes it easier to control while keeping one had on your funnel.

You want to fill the bottles right to the top. Other home brews, such as beer or wine, leave head space at the top in order to allow for the formation of froth. In our case, we want the least amount of oxygen possible. The less oxygen in the bottle, the more carbon dioxide will form – which means more fizz!

4. Seal Your Bottles And Store Them In A Warm Location

Keeping an airtight steal is essential. That’s why picking the right bottles for your kombucha is important. Personally, I always use the classic flip-top bottles. After having a beer bottle explode on me I always prefer to have the safety flip-top bottles provide.

Flip-top bottles are the safest bottle to use for the second fermentation

Once you have your airtight seal, let the bottles sit in a room-temperature location for at least 3-4 days. If it’s possible to store the bottles somewhere that is warmer than room temperature (say, like on top of your fridge) but away from sunlight your kombucha will have even more carbonation.

If you are worried that your bottles are building up too much carbonation, you can always “burp” your bottles for piece of mind. Just don’t do it too much or else you will lose all the carbonation you’ve been building.

5. Place Your Bottles In The Fridge

After 3-4 days, test your kombucha to taste the carbonation level. If it’s still to flat for your liking you can leave it out for another day or so.

When finished, you’re going to want to store your bottles in the fridge. This slows any additional fermentation and locks in the taste and carbonation levels.

You can store the kombucha in the fridge for a number of weeks before it begins to get too sour. Kombucha will never go “off” – rather, it will just continue to slowly ferment until it begins to take on a vinegary flavor.

Alternative Flavor Method For The Secondary Ferment

There are three ways to flavor your kombucha:

  1. During the primary ferment
  2. During the secondary ferment in bottles
  3. During the secondary ferment before bottling

There are pros and cons to each. For instance, if you’d like to try out a number of different flavors with a single batch, you need to be flavoring in bottles. But, if you’re only going to use a single flavoring agent, you may want to consider favoring before bottling.

To flavor before bottling just follow these simple steps:

  1. Remove the SCOBY from the vessel
  2. Add in your flavoring agents
  3. Cover the vessel with a cloth and allow the brew to sit for 3-4 days. 
  4. Remove the flavoring agent and pour the kombucha into bottles. Seal the bottles tightly and let them sit at room temperature for 3-4 days.

The benefit to this method is you are not having the flavoring agents floating around inside the bottle. Which can be a big plus if you are trying to sell your kombucha on the side.

Additionally, there is a small risk that the flavoring agents going off if you let them sit in the bottle for weeks on end. Personally, I’ve never had any issue with this, but it’s something to consider.

Lastly, cleaning flavoring agents out of the bottles can be a pain if you don’t have an appropriate bottle brush.

The downsides to the method are you only get to pick a single flavoring for each brew. This can really limit your ability to experiment with new flavoring techniques. Alternatively, you can separate a bottles worth into different containers and flavor them individually if you’re really concerned with having flavoring in the bottles.

The other downside to this method is you usually end up with less carbonation. The flavoring agents typically supply another form of sugar that can be used by the yeast for extra fermentation.

Flavoring The Primary Brew

Your other option is to flavor the primary brew.  This is a perfectly viable option, but it does carry a small amount of risk.

If your flavoring agent reacts poorly with the SCOBY you run the risk of ruining an entire batch. However, this isn’t very common. As long as you stick with the common flavoring agents you should be fine.

When you flavor the primary brew the kombucha has a lot longer to absorb the flavoring agent. This is the reason the flavors are usually much more intense when you flavor the primary. As I’ve mentioned in previous post, because kombucha is so acidic it tends to make everything it touches more bio-available.

It has the tendency to soak up flavors quickly – hense the power of flavoring your primary.

You also need to consider the overall health of your SCOBY when you flavor the primary. Different flavoring agents will react differently with your SCOBY. Some may even weaken it to a point where your flavors will be off a few generations later. This is why I always recommend you use a spare SCOBY from your SCOBY hotel anytime you want to play with the primary ferment.

Always use a spare SCOBY from your hotel when you flavor the primary

I’d recommend trying to flavor your primary only if you’re looking for an extra strong flavor in your kombucha.

How To Increase The Carbonation During The Secondary Ferment

There really is only one area where we get to control the carbonation: in the bottles. While there is a natural build-up of carbonation during the primary ferment, most of it is vented off before we get a chance to consume it.

It’s good to keep in mind that lots of commercial kombucha has added in extra carbonation. This is why you may struggle to get the same level of carbonation as you’ve been used to from store bough kombucha.

Before we get into how to increase the carbonation levels, it’s necessary to understand how the carbonation is formed in the first place.

How We Get Carbonation In Kombucha

Carbonation is formed from dissolved carbon dioxide. As long as there is no way for the CO2 to escape, it will remain in the liquid. When the pressure is released, the CO2 begins to leave the bottle.

Where is the CO2 coming from?

Well, it just so happens that one of the by-products of fermentation is CO2 (along with alcohol.) Therefore, when we cut off the oxygen supply of the SCOBY and force it into fermentation, carbon dioxide is produced that is trapped inside the bottle.

Primary ferments also build-up carbonation naturally (although much less than bottles) because the layer of SCOBY prevents the CO2 from escaping.

How To Boost Carbonation

There are a handful of tricks we have up our sleeve to increase the carbonation levels in kombucha. The first, add a new source of sugar inside the bottles.

1. Add A Source Of Sugar Inside The Bottles

By adding a new source of sugar inside the bottle you boost the yeast’s production of carbon dioxide. You juts have to be careful that the new sugar supply isn’t too sweet.

Too much sugar in the secondary ferment will result in an overly sweet kombucha.

A few small pieces of fruit will do the trick. I recommend trying pineapple or strawberries. This will both flavor the kombucha as well as increase the carbonation.

  • For fresh fruit use 1 tablespoon
  • For fruit juice use about 6 tablespoons 

2. Fill The Bottles Right To The Top

The more oxygen in the bottle the less carbonation. We want to cut off the oxygen supply as soon as possible during the secondary ferment. This means you want to fill your bottles right to the top.

3. Add Ginger

Small pieces of ginger has always been a go-to for generations of kombucha brewers. No only does it produce the classic kombucha ginger flavoring, it also increases carbonation.

If you really want to boost your carbonation, add up to a teaspoon of ginger. The natural sugars in ginger kick the dormant yeast into high gear – producing lots of extra bubbles. Adding a little bit of lemon can really pair well with the ginger flavor.

4. Add In Eggshells

I know it sounds weird, but this has always been an old trick of kombucha brewers. You don’t need to use much to get an extra punch of fizz.

Wash the egg shells thoroughly and then bake them in the oven at 250°F for 10 minutes. Next, grind them up as small as you can – the more surface area the better.

When bottling your kombucha, place 1/4 teaspoon in each bottle.

The eggshell will not only provide you with extra carbonation, the extra calcium and trace minerals will provide you with a little nutritional boost!

Using The Right Bottles For The Second Fermentation

Because this is the stage of brewing where there is the most pressure build-up, it’s also the stage where things can go horribly wrong.

Kombucha bottle explosions are rare, but the do happen.

Because they were so cheap, I wanted to try using beer bottles for kombucha. Unfortunately, the lids on beer bottles are secured so tightly that the bottle explodes before the cap pops off.

From that moment on I’ve only used flip-top bottles. Because of the lid mechanism, the seal will pop off long before any dangerous explosions.

Flip-top bottles also have a nice thick seal that is great for sealing in the carbonation. Additionally, the bottles rarely have to be replaced. When the seal becomes worn out, simply replace the seal!

No matter what bottles you use, you always want to fully inspect them for any cracks or weak points.

Always inspect your bottles for cracks or weak points

How Long Should My Second Ferment Be?

This is a common question that is asked a lot. The answer is: it depends. 

It depends on the following:

  • The strength of your SCOBY
  • How much sugar you’ve added
  • How carbonated you like your kombucha
  • What you add for your flavoring
  • The temperature of primary and secondary ferments
  • The the type of bottles you use

With all of these factors at play, you can expect a lot of variability in the lengths of the second ferment.

What that being said, most brews only need somewhere between 3-5 days to fully carbonate. They will also continue to ferment, albeit slowly, in the refrigerator. So if you’re not completely satisfied with the level of carbonation you can always let them age in the fridge for a few days.

I’ve even heard of people who like to let their kombucha age in the fridge for a couple of weeks before they drink them.

It’s all very circumstantial. That’s half the fun of being a home brewer. You get to play and experiment with different brewing techniques and recipes to create your own unique kombucha.

To Burp Or Not To Burp

Burping kombucha bottles during the second ferment is another controversial topic among brewers. Some say you should know your brewing techniques well enough to never have the need to burp your bottles. While others say it’s just good practice.

Burping your bottles refers to the practice of quickly breaking the seal on the bottle to release the pressure built up from the CO2.

Personally, I only burp the bottles when I have an extra strong brew with carbonating agents in the bottle – ginger for example.

If I’m just brewing plain-Jane kombucha, I won’t worry about burping the bottles because this always leads to a flat kombucha.

If I’m unsure of a new brew, I will usually burp one bottle to test the carbonation levels. If I hear a significant release of carbonation, I burp the other bottles.

When To Burp Your Bottles

You’ll want to consider burping your bottles in the following cases:

  • Extra carbonating agents added such as fruit, ginger, eggshells, etc.
  • You’re using bottles styles other than flip-top
  • You’re a complete beginner
  • You’re using an extended second ferment

Adding extra carbonating ingredients can lead to unexpected levels of carbonation. If you aren’t familiar with the levels of carbonation in your bottles, it can be a good idea to burp them every few days.

As I mentioned before, every other bottle besides flip-tops don’t have a built-in safety mechanism. Therefore, if you’re unsure of the carbonation levels of a new brew, you may way to consider burping one or two to check the carbonation levels.

Burping bottles is a good practice if you are completely new to home brewing. Until you get a sense of the carbonation levels inside your bottles it’s safer to burp.

When Not To Burp Your Bottles

If you’ve been struggling to get the carbonation levels you’d like then you need to stop burping your bottles.

I won’t burp my bottles unless I’m doing something out of the ordinary that causes more carbonation build-up.

How To Avoid A Kombucha Geyser

Every home brewer will have a story of a kombucha geyser.

A kombucha geyser is when the carbonation has built up to a level that your kombucha comes shooting out when you open the bottle.

The best way to avoid this is through experience and regular burping.

If you expect a kombucha geyser just get a large bowl and a dish towel to stop the kombucha from spreading too far!

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