What is a fermentation airlock and should I use one?

In fermentation an airlock is a set up that allows the carbon dioxide gas created as the bacteria break down the sugars and starches to escape the fermentation vessel, without letting new air into the environment.  There are many ways to achieve this airtight environment and it often involves a bit of water. The ceramic water-seal crocks were likely one of the first ways that humans figured out that a simple ring of water would trap the air.

Airlocks like the ones pictured above also use water as the seal. The carbon dioxide bubbles out through the water but the outside air can’t find a path back through the water and into the ferment. Simple ones like these have been used in alcohol ferments for years but as lactic acid fermentation has gained popularity many folks have adapted these to use on canning jars. (Spoiler alert: there is a giveaway for a set at the bottom of this post.)

These systems take most of the babysitting out of the curing time during the fermentation. We admit to setting ferments in their air lock topped jar and forgetting them—with delicious results. That said, its only fair that you know all ferments have a mind of their own (just like kids). So while you think they are safely sleeping in bed, they just might be under the covers reading ghost stories with a flashlight. Then they get scared and there is a whole lot of excitement…same with the microbes.

If your ferment is particularly active and your jar is particularly full this moving brine may just bubble right out of your ferment. When the ferment appears to be “making” brine what is really happening is it is expanding due to the trapped carbon dioxide. This movement in the brine is sometimes called a “heave” or a “surge.” Therefor weights are another important piece of the worry-free ferment as they help keep the veggies in place during the most active phases of fermentation. We have found out ferments are infinitely more successful if we manage the air pockets. Even if the oxygen is not present and the vessel is completely sealed in these pockets the flavor can have a bitter quality if they aren’t pressed down. This brings us back to using small weights or simply opening your ferment as needed to press the veggies back down under the brine (with a clean utensil) before sealing it up again for more fermentation.

So, the second part of the title—should you use an air lock? We hope we have given you some information to help you decide. Kirsten collaborated in December with Mara Rose of Hatchlab.net in reviewing four fermentation systems. In this project we reviewed the systems but also gave you a peak at the folks who designed them.