During second fermentation yeast will settle to the bottom of the bottles or second fermenter, yielding a less hazy carbonated product. Many people shie away from making fermented drinks because of a “explosion” from overly-pressurized bottles. I had multiple bottles explode while making ginger beer, sending glass shards flying everywhere. Pressure can be a dangerous thing! But more on that in a little bit; first, why do we bottle these things?
Most of the time, ferments get pressurized during a step called a second ferment. The primary purpose for a second ferment is to allow a drink to get carbonated, so it’s fizzy like soda or beer. This is an optional step, but many people choose to do a second ferment with kombucha, water kefir, milk kefir, homemade soda, beer, and champagne. For example, the first ferment for kombucha usually takes around 7 – 10 days, at which point it is bottled and allowed to ferment in the bottles (the second ferment) for another 1-3 days or so. Another reason to do the second ferment is to add other flavors to it; for example, many people will add fruit juice or even chunks of fruit to their water kefir when they bottle it.
Second Fermentation: Warning!
The only way to allow carbonation to build up in the drink is to have the bottle sealed. Here is where the potential for danger comes in: if the bottle isn’t designed to hold pressure, it can explode! That’s what happened to my ginger beer: I had just put it in a bunch of random bottles that couldn’t handle the pressure. They didn’t stand a chance.
So, what is a safe way to bottle your brew and do a second ferment? Here are some of your options:
Put them in bottles designed for the pressure – bottles for fermented drinks. My favorites are the swing-top bottles, which are the same ones that some kinds of beer, kombucha, and water kefir are sold in. These are strong bottles, and the swing-top lids are strong enough to hold the pressure in. I also re-use kombucha bottles from the store. I like the ones from GT’s kombucha, and I have collected quite a few of them over the years. Some experienced brewers re-use plastic 1-liter or 2-liter soda bottles; these will do the job very well, but they are still plastic.
Burp them regularly. Pressure will build up in all kinds of bottles during the second ferment, but if you let it out regularly, it won’t build up to dangerous levels. This method can also let you know how quickly the second ferment is happening because a faster ferment will produce more gas. But, if you’re not using pressure-safe bottles, you need to remember to do this at least twice a day, maybe even more if you added fruit or juice to your second ferment!
Put them in the fridge. Putting the bottles in the refrigerator will slow down the fermentation, and will also cause the carbon dioxide gas to dissolve better–in other words, it stays in the liquid instead of making bubbles. The combination of these two factors means that it’s unlikely that a refrigerated drink will explode. But, if you’re not using a pressure-safe bottle, you should probably drink it or burp it within a couple of days, just to be safe!
Making your own carbonated, fermented drinks is fun and really rewarding, especially if you’re trying to break a soda habit. These are so much healthier, with less sugar, better ingredients, and–of course–the probiotics! Don’t get too scared by the possibility of breaking bottles. Since my first experience with my ginger beer, I’ve never had another bottle break!