How Does Fermentation Work?
In lacto-fermentation, beneficial bacteria convert sugars into lactic acid under a salt brine and without oxygen, preserving food and developing its tangy flavour. A fermentation kit keeps vegetables submerged and air out while carbon dioxide escapes through an airlock or valve.
How a ferment happens
Salt and water set the stage
Weights hold food under brine
An airlock lets gas out, air stays out
Bacteria sour and preserve the food
Fermentation kits all serve one goal: to create a stable, oxygen-free environment where vegetables can ferment cleanly under a salt brine. Understanding that goal explains every part in the box.
What is happening in the jar
Lacto-fermentation is driven by beneficial bacteria that are naturally present on vegetables. Submerged in a salt brine and kept away from oxygen, they convert sugars into lactic acid, which preserves the food, develops its tangy flavour, and creates an acidic environment that discourages harmful microbes. The salt slows the wrong bacteria early on and helps the right ones take over. The kit's job is simply to keep the food under the brine and the oxygen out while carbon dioxide escapes.
What each part does
| Part | What it does | Why it matters |
|---|---|---|
| Airlock or valve | Lets CO2 escape, keeps air out | Prevents pressure build-up and contamination |
| Weight | Holds vegetables under the brine | Food above the brine can mold; this is the key |
| Vessel (jar or crock) | Holds the ferment and brine | Jars for small batches, crocks for volume |
| Brine (salt + water) | Creates the fermenting environment | The right salt level guides a clean ferment |
Valve vs water-seal airlocks
Mason jar kits usually use a silicone one-way valve or a small water airlock in the lid: gas pushes out, nothing gets in. Traditional crocks use a water moat, a channel around the rim that the lid sits in, so gas bubbles out through the water while air is sealed off. Both achieve the same anaerobic result; the crock simply does it at larger volume.
Frequently asked questions
Why does fermenting need to be oxygen-free?
The beneficial bacteria that produce lactic acid work without oxygen, while many spoilage organisms need air. Keeping the ferment submerged and sealed lets the right bacteria dominate, which is why weights and an airlock matter.