Fermentation Crocks, Jars & Airlocks: A Buying Guide

Picking the right vessel makes fermenting easier and more reliable. Here is what a crock, a mason jar airlock kit, and an all-in-one system each do well, what size to buy, and the mistakes worth avoiding before you spend any money.

The vessel: crock, jar, or all-in-one

There are three common paths, and each suits a different fermenter.

Stoneware crocks US-made Ohio Stoneware crocks (1–10 gal) are dishwasher safe. German and Polish water-seal crocks (Harsch, K&K Keramik, Boleslawiec) run 7.5–50L with lead-free glaze but are hand-wash only.

Mason jar airlock kits Kraut Source uses a steel water-moat lid, Easy Fermenter uses a waterless valve with a hand pump, and Masontops Pickle Pipe is a one-piece silicone valve. All turn a regular jar into a small fermenter.

All-in-one systems Humble House/SAUERKROCK is a small ceramic crock (2–10L) and Fermentools converts any mason jar into an airlock fermenter. Both skip manual burping entirely.

Water-seal crocks all work the same way: a water-filled moat lets gas escape while blocking air and mold from getting in.

What size to buy

Sizing is simple once you know the ratio.

1 gal crock per 5 lbs of cabbage

5L the most common household sweet spot

1–2 in headspace to leave above the brine

Bigger is not always better — a crock that is too large for the batch leaves more air space above the brine, which can invite mold at the surface.

Airlocks vs. manual burping

Both methods manage the same problem — CO2 building up inside a sealed vessel — but they handle it differently.

Airlock a one-way valve that lets CO2 out but blocks oxygen, mold spores, and fruit flies from getting back in. Maintaining this seal is one of the most effective ways to keep pathogens out.

Manual burping loosening the lid once or twice a day works fine, but briefly lets in air each time and depends on you remembering to do it.

Water-seal crock the moat self-vents gas continuously, so there is nothing to remember once the moat is filled.

All-in-one systems Fermentools and similar kits are built to skip burping altogether.

For a full breakdown of how often to burp and the warning signs of too much pressure, see our guide on burping fermentation jars.

What to check before you buy

A few checks separate a safe, long-lasting piece of equipment from one that fails early.

1
Look for lead-free glaze Check for explicit "lead-free glaze" or "food-safe" labeling on any imported ceramic crock — the FDA has flagged lead risk in some imported glazed pottery.
2
Inspect the glaze A smooth, even glaze with no cracks or crazing is safer. Cracks and crazing can harbor bacteria over time.
3
Confirm the seal Check that the moat or gasket is intact. A dry moat or worn gasket breaks the anaerobic seal that keeps a crock working.
4
Check care instructions US-made Ohio Stoneware is dishwasher safe, but most imported ceramic crocks are hand-wash only — confirm per product before you buy.

Weights and other essential extras

A weight keeps vegetables fully submerged, which is the single biggest defense against surface mold.

Glass weights Non-porous and easy to see through to check the ferment underneath.

Ceramic weights More porous than glass, but often bundled free with crock kits.

Sizing Wide-mouth jars need roughly 2.75in (70mm) weights, regular-mouth jars roughly 2.1in (53mm), leaving about a 1/4in gap for CO2 to escape.

Weights and airlocks solve different problems, so many experienced fermenters use both together — the weight keeps vegetables under the brine and the airlock manages the gas.

Cost to expect

$10–40 mason jar airlock kits

$21–135 US-made stoneware crock kits

$85–250+ imported European crocks

Common beginner mistakes

! Watch for

Wrong headspace — too little causes overflow, too much raises mold risk
Skipping or under-sizing the weight, letting vegetables float and mold
Letting a crock moat dry out, which breaks the seal
Using detergent on ceramic crocks instead of plain water
Using a cracked crock, which can no longer seal or be sanitized properly

Once you have the right vessel, dialing in the salt is the next step — see our guide on lacto-fermented vegetables or jump straight to the numbers.

Try the calculator

Fermentation Brine Calculator

Enter your vessel size and target percentage to get the exact grams of salt and water.

Open calculator →

Frequently asked questions

What size fermentation crock should I buy?+

A common sizing rule is 1 gallon of crock for every 5 lbs of cabbage or vegetables. For most households, a 5-liter (about 1.3 gallon) crock is the most common sweet spot size. Leave 1–2 inches of headspace between the brine and the rim.

Do I need an airlock, or can I just burp the jar?+

Either works. An airlock is a one-way valve that lets CO2 out but blocks air, mold spores, and fruit flies from getting back in, so it needs no daily attention. Burping — loosening the lid once or twice a day — works fine too, but briefly lets in air each time and relies on you remembering to do it.

Are ceramic fermentation crocks safe?+

Look for explicit "lead-free glaze" or "food-safe" labeling before buying, since the FDA has warned about lead risk in some imported glazed pottery. Also check for a smooth, even glaze with no cracks or crazing, which can harbor bacteria.

Glass or ceramic fermentation weights — which is better?+

Glass weights are non-porous and let you see through to check the ferment. Ceramic weights are more porous but are often bundled free with crock kits. Either works well as long as it is sized to leave a small gap for CO2 to escape.

Can I ferment in a regular mason jar?+

Yes. Mason jars are a fully acceptable fermenting container as long as vegetables stay submerged under the brine with a weight, and there is a way for gas to escape — either an airlock lid or manual burping.

How much does basic fermenting equipment cost?+

Mason jar airlock kits run about $10–$40. US-made stoneware crock kits run roughly $21–$135. Imported European crocks cost more, often $85–$250 or higher. All-in-one ceramic systems typically land around $60–$100 or more.