Fermentation Airlocks

When vegetables start to ferment, gasses are produced, such as hydrogen, methane, and carbon dioxide. Some of these gasses are quite strong smelling, especially when fermenting members of the cabbage family.

What if you ferment with no lid?

This is called open fermentation, with no lid or only a cloth as a covering. This leads to a high risk of contamination by unwanted moulds and bacteria, causing spoilage of the ferment. The unhealthy bacteria and moulds that we don't want in the ferment are called pathogens. The pathogens need oxygen from the air to multiply.
The lacto fermenting bacteria and yeast, that are good for us and do the work of turning the raw vegetables into healthy fermented food, need to live with no oxygen.

Insects and vermin are attracted to the smell of fermenting food, keeping a closed container stops the smells from escaping.

The carbon dioxide that is produced by the fermenting bacteria is beneficial to the process, acting as a preserving layer above the brine, keeping the oxygen out. With no lid all the carbon dioxide will be lost.

Kahm is a yeast that grows on the top of the brine if there is oxygen present. It is harmless, but does affect the flavour of the ferment, imparting a musty flavour.

What happens when you close the container?

When you seal the jar with a lid, the gas being made will cause a build-up of pressure. This pressure needs to be released, otherwise the container will break or even explode.

The lid needs to be slightly opened at least once a day, to release some of the pressure build up, this is called ‘burping’. Many people ferment this way, but it does have its disadvantages.

Not only the extra attention needed, burping allows the gas and smells out. When the container is burped, fresh air containing oxygen and unwanted moulds and bacteria are let back in. The good bacteria we want to encourage, don’t want oxygen, the bad bacteria that spoil the food are oxygen loving.

The easy way to control the ferment

The easiest way to let the gasses escape, while keeping the air out is by using a one-way airlock system.
An airlock is not a must have tool, but it makes the process easier, more consistent, stops odours leeching out into the room and makes the ferment less prone to spoilage.

The way an airlock works is buy letting gasses escape, usually through a water trap. The gas travels through the water as bubbles. The water captures the smells, while stopping outside air from getting back into the container. Airlocks stop the unwanted oxygen loving organisms entering the container, greatly reducing the risk of unhealthy contamination.

An ancient fermenting container is a ceramic or glass crock

A crock has a gutter or moat built into the rim. The moat is filled with water, then an upturned bowl is placed on the rim. The water acts as a seal. The outside air is prevented from entering the crock, while gasses bubble out through the water.
The water in the moat can evaporate, so that needs to be checked every now and then.

The crock needs to be made of food grade materials. Some glass and ceramic glazes can leach chemicals especially with acidic contents, make sure every container that comes in contact with the food is food safe. If the crock is ceramic it's not easy to see what's going on, there could be mould or bad bacteria growing t, hiding out of plane site. Glass jars are especially good for people just starting out on their fermenting journey, you can watch the changes happening to your ferment, catching problems early on.

Since crocks are usually large, they are useful for making large quantities of vegetables.

Waterless airlocks

Pickle Pipes are a waterless one-way silicon valve that is made to fit the top of a mason jar. Mason jars come in 2 sizes 86mm and 70 mm. The Pickle Pipe has a raised nipple with a small cross cut into it, allowing the pressure inside the jar to push open the pipe when needed. They are held in place with a metal band and come in arrange of colours.

Pickle Pipes work well at expelling the gasses, but having no water barrier the smells also escape. I wouldn’t recommend them for making a strong smelling ferment such as kimchi.

Small water filled airlocks

An S-shaped airlock is made of 2 vertical chambers connected by a pipe, acting as a drain trap. The gas travels through the water then is released. The water in the airlock is the barrier between the air in the container and the outside air.
There is usually a small lid on the airlock, they aren't well fitting, allowing the gas to escape after it has bubbled through the water.

The 3-piece airlock works the same as a crock with a moat. The bottom chamber is filled with water. The second piece is upturned and put into the bottom chamber. The second piece is now sitting in the water, making a water trap.
A lid, the 3rd piece, sits on the top, stoping the evaporation of the water. Like the S- shaped air-lock the lid isn't a tight fit, letting the gasses out.

Both types of air-locks both do an excellent job of releasing the internal pressure and keeping the system closed.
The 3-piece airlock is easier to clean after use.

My preference is the S-shaped airlock, as they are less prone to breakage and have less pieces to get separated in the kitchen draw.
These small airlocks are great for small batch fermenting, especially when starting out. But they can also be put on a large bucket, they are used this way when making beer.

With these types of air-locks, you’re not committed to a huge crock full of food. You can use small jars making small batches. Having several ferments going at once you can experiment with flavours, vegetable combinations and fermenting times.

How to use an airlock

The small airlocks are ½ filled with water. Tap water is ok, since none of it will come in contact with the brine. The bottom tip is pushed into a silicon gromet that sits in a hole in the lid. Push the airlock through the hole into the air space until the tip is siting above the brine. The tip shouldn’t touch the brine, or some will be drawn back up into the water reservoir, making the water in the airlock dirty.

You can now set the jar aside to ferment, no burping is necessary. The bubbles of gas will start to escape on their own as the pressure builds up.
Just check for readiness to eat, you can open the jar and taste some after 4 to 5 days. If you are happy that it is acidic and fermented enough, it can be placed in the fridge to halt the fermenting process, otherwise leave it to ferment for longer.

When the fermented food is placed in the fridge, the airlock is no longer needed as no more gasses will be made. A lid with no hole can replace the airlock lid, or transfer the food to a food safe container.

Cleaning the airlock

The airlock needs to be thoroughly cleaned in between use. Wash and soak in warm soapy water, then rinse with clean water and leave to thoroughly dry. They can be sanitized in the solutions used for cleaning baby milk bottles, following the product instructions.

Waterless airlock

3 piece airlock