Fermentation crocks
The stoneware crock is the traditional vessel for sauerkraut and pickles. The types there are, how a water seal works and how to tell whether a glaze may carry lead.
6 min read Getting good Reviewed October 27, 2026 40 facts, each with its source
What a fermentation crock is
Sauerkraut has traditionally been made in a large stoneware crock1: a thick-walled pot of fired clay, glazed inside. It does what a jar does. It keeps the vegetables under their brine, away from air, while they ferment. Its advantage is size: a crock holds in one go the pounds of cabbage or cucumbers that would otherwise fill a dozen jars.
You don't need a crock to ferment. Food-grade glass and plastic containers are excellent substitutes2. Mason jars work too, although you may lose more batches with them3.
Three kinds of crock
| Kind | How it closes | What you do |
|---|---|---|
| Open | A plate that nearly fills the mouth, a weight and a cloth on top4 | With jars as weights, check it 2 to 3 times a week and skim off any film5 |
| Lidded | A lid that fits properly6 | Check that the vegetables stay submerged |
| Water-sealed | A lid that sits in a groove filled with water7 | Keep the groove from drying out |
A crock's shape doesn't affect the ferment's safety, although it can change its quality8. The same thing rules in all three: the brine has to cover the vegetables by 1 to 2 inches (2.5 to 5 cm)9. If your weight is a bag of brine, leave the crock alone until the bubbling stops10.
The water-sealed crock
Some crocks have a groove around the rim that the lid sits in. The groove is filled with water, and the water works as a seal that keeps oxygen out7. Fermentation gas bubbles out between the lid and the water. It's an airlock, like the one on a carboy, only as wide as the crock.
They usually come with two half-moon ceramic weights that sit on the vegetables. If you use others, make sure they are food-grade: weights that aren't may contain lead11.
They need two things from you:
- Don't let the groove dry out. In heat or dry air, the water evaporates. Check the level every few days and top it up.
- Don't lift the lid without a reason. These crocks ferment better when they stay closed, which can be hard for curious cooks12.
What size you need
You need a 1-gallon (4-liter) container for every 5 lb (2.3 kg) of fresh vegetables13. A 5-gallon (19-liter) crock is just right for about 25 lb (11 kg) of cabbage or cucumbers14.
Fill it only about three-quarters full and leave 4 to 5 inches (10 to 13 cm) of headspace15. With the gas of the first few days, everything rises. Salt is worked out as in a jar, on the weight of the vegetables: the salt calculator gives you the grams for any amount.
Lead in glazes
Clay is glazed so it stops being porous. When a piece is fired at the right temperature for the right time, nearly all the lead in the glaze stays bound in it. When it isn't, lead can reach the food16. Some glazes aren't acid-safe and can leach heavy metals17, and lead leaches into food mostly under acidic conditions18. A ferment is exactly that: something acidic, for weeks.
That's why the guides say not to use lead-glazed crocks19, or ceramic for kombucha20. There have been cases of lead poisoning from glazed containers used to ferment highly acidic teas21. Lead glazes are common in crocks made before the 1970s22, the ones that get inherited or turn up in an attic.
Lead affects infants, young children and the developing fetus most, even at exposures that cause no obvious symptoms23. If you've used a doubtful pot and you're pregnant or there are children at home, talk to your doctor.
How to tell whether a crock can be trusted
The FDA, the U.S. food and drug agency, asks you to look more carefully at pieces that are:
- Handmade, with a crude look or an irregular shape24.
- Damaged or heavily worn25.
- Bought at flea markets, or from a maker you can't identify26.
- Decorated in bright orange, red or yellow, because lead is used to intensify those colors27.
Factory-made ceramics meant for everyday use cause far fewer problems28. But a “lead free” label isn't enough: the FDA has found traditional pottery labeled that way with as much extractable lead as lead-glazed pottery29.
If you're unsure:
- Test it. Lead test kits are sold in hardware stores and online30. If it tests positive, the FDA strongly advises against using the piece for cooking, serving or storing food31. If it tests negative, that isn't enough: kits don't detect lead beneath the surface, and a negative result doesn't ensure the piece is free of it32.
- Look at the bottom. Decorative pieces may have a warning stamped on them, such as “Not for Food Use—May Poison Food.” Don't use them with food33.
- If you can't check it, don't use it with food34. Washing or boiling won't help: nothing removes lead from pottery35.
It's a house rule: an old, inherited or handmade crock stays on the shelf as a decoration, even if the kit comes up negative. For fermenting, use a factory-made crock sold as food-safe.
Before you use it
- Look it over. If it has chips or cracks, use another container36. Deep scratches and chips can harbor bacteria37.
- Wash it. The crock, the plate and the jars are washed in hot soapy water and rinsed well with very hot water before use38.
- No wood, no metal. Wood is hard to keep clean39. Metal, other than high-grade stainless steel, degrades with salt and acid40.
Where every number comes from
Every number in the text leads to its figure: the exact sentence from the official guide it comes from, in its own language.
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1
Sauerkraut has traditionally been made in a large stoneware crock
“Sauerkraut has traditionally been made in a large stoneware crock.”
Washington State University Extension, Lewis County · Sauerkraut Making · read on October 26, 2026
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2
Food-grade glass and plastic are excellent substitutes for a crock
“Food-grade plastic and glass containers are excellent substitutes for stone crocks.”
National Center for Home Food Preservation (USDA, University of Georgia) · Suitable Containers, Covers, and Weights for Fermenting Food · read on October 26, 2026
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3
Jars work, but you may lose more batches
“Fermenting sauerkraut in quart and half-gallon Mason jars is an acceptable practice, but may result in more spoilage losses.”
National Center for Home Food Preservation (USDA, University of Georgia) · Suitable Containers, Covers, and Weights for Fermenting Food · read on October 26, 2026
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4
Without a fitting lid, use a plate; the ferment must be covered
“If a fitting lid does not accompany the crock, a plate or similar cover can be used. It is important to cover the product for both safety and quality.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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5
With jars as weights, check it 2 to 3 times a week
“If you use jars as weight, you will have to check the kraut 2 to 3 times each week and remove scum if it forms.”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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6
With a crock or a pail, a properly fitting lid
“If you are using a fermentation crock or a plastic container, use a properly fitting lid.”
University of Minnesota Extension · Preserving food at home: Fermentation (reviewed 2026) · read on October 25, 2026
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7
The rim groove, always full of water, keeps oxygen out
“Other crocks have specialized rims with grooves or gutters in which a lid fits snuggly within. The groove or gutter must be kept constantly filled with water to provide a seal that keeps oxygen out.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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8
A crock's shape doesn't change safety, but it can change quality
“The shape or style of crock does not affect product safety but could affect quality.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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9
Brine 1 to 2 inches above the vegetables
“it is important to have the brine/juices stay 1-2 inches above the fermented vegetables.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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10
With a brine bag, leave it alone until the bubbling stops
“If you weigh the cabbage down with a brine-filled bag, do not disturb the crock until normal fermentation is completed (when bubbling ceases).”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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11
Weights that aren't food-grade may contain lead
“Do not use weights that are not intended for food use because they may contain harmful compounds such as lead.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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12
These crocks ferment better if the lid stays on
“These specialized crocks ferment better if the lids are not removed or disrupted, which might be difficult for curious cooks.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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13
A 1-gallon container for every 5 lb of vegetables
“A 1-gallon container is needed for each 5 pounds of fresh vegetables.”
National Center for Home Food Preservation (USDA, University of Georgia) · Suitable Containers, Covers, and Weights for Fermenting Food · read on October 26, 2026
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14
A 5-gallon crock for about 25 lb of cabbage or cucumbers
“a 5-gallon stone crock is of ideal size for fermenting about 25 pounds of fresh cabbage or cucumbers.”
National Center for Home Food Preservation (USDA, University of Georgia) · Suitable Containers, Covers, and Weights for Fermenting Food · read on October 26, 2026
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15
Leave 4 to 5 inches of headspace and fill it about three-quarters
“If using a large container or crock, leave 4 to 5 inches of headspace in your container. It should be about 75 percent full.”
University of Minnesota Extension · Preserving food at home: Fermentation (reviewed 2026) · read on October 25, 2026
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16
Properly fired, the lead stays bound in the glaze; poorly fired, it can reach the food
“When the pottery is fired at the proper temperature for the proper amount of time, essentially all the lead is bound into the glaze. If any migrates to food, it will be an insignificant amount. However, if not properly fired, the lead may not fuse to the earthenware and may contaminate food when the pottery is used with food.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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17
Some glazes aren't acid-safe and can leach heavy metals
“Some pottery glazes are not acid safe and may leach contaminants such as heavy metals into the food if used.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.1: Fermented Vegetables (August 2024, updated December 2024) · read on October 25, 2026
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18
Lead leaches into food mostly under acidic conditions
“Lead from paint or glaze can leach into the food, most often under acidic conditions.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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19
No lead-glazed crocks
“Do not use copper, iron, or galvanized metal containers or lead-glazed crocks”
University of Illinois Extension · Fermentation handout (2020) · read on October 20, 2026
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20
Kombucha goes in neither ceramic nor lead crystal
“Because of the acidity of Kombucha tea, it should not be prepared or stored in containers made from materials such as ceramic or lead crystal, which both contain toxic elements than can leach into the tea.”
CDC, MMWR 44(48):892 · Unexplained Severe Illness Possibly Associated with Consumption of Kombucha Tea -- Iowa, 1995 · read on October 20, 2026
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21
Lead poisoning has occurred when acidic teas were fermented in glazed containers
“Lead poisoning has occurred when inappropriate glazed containers were used to ferment highly acidic teas over time.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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22
Lead glazes are common in crocks made before the 1970s
“When choosing a crock, it is important to ensure that the paint or glaze does not contain lead, which is often found in crocks made before the 1970s.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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23
Lead affects infants, young children and the fetus even without obvious symptoms
“infants, young children and the developing fetus can be affected by chronic exposure to amounts of lead that may not result in obvious symptoms of lead poisoning.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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24
Handmade pieces with a crude look or an irregular shape
“handmade with a crude appearance or irregular shape”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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25
Damaged or heavily worn pieces
“damaged or excessively worn”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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26
Pieces from flea markets, or from a maker you can't identify
“purchased from flea markets or street vendors or if you are unable to determine whether the pottery is from a reliable manufacturer”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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27
Bright orange, red and yellow: lead intensifies those colors
“brightly decorated in orange, red, or yellow color, as lead is often used with these pigments to increase their intensity.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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28
Factory-made everyday ceramics cause far fewer problems
“Pottery not listed above that was made in commercial factories for everyday use is much less likely to have problems related to lead.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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29
Pottery labeled “lead free” with as much lead as lead-glazed pottery
“traditional pottery from several manufacturers in Mexico labeled as “lead free” in fact contains levels of extractable lead comparable to levels that may be found in lead glazed pottery”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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30
Lead test kits are sold in hardware stores and online
“Consumers can buy lead-testing kits in hardware stores or online.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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31
If it tests positive, the FDA advises against using it with food
“If a consumer performs a test and finds the pottery contains leachable lead, the FDA strongly advises against using the pottery for cooking, serving, or storing food or drinks.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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32
Kits miss lead beneath the surface: a negative result guarantees nothing
“If lead is beneath the surface of the dish, the test kits will not detect it. If the test kit is positive, the dish should not be used for food or drinks. A negative result does not ensure that the dish is safe.”
Los Angeles County Department of Public Health · Lead in traditional ceramic dishware · read on October 27, 2026
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33
Decorative pieces may carry a warning on the bottom
“If the pottery was manufactured for use only as a decorative item, it may have a warning stamped onto the clay bottom such as “Not for Food Use—May Poison Food.” Do not use items with this type of warning for cooking, serving, or storing food or drinks.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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34
If you can't check it, consider not using it with food
“If you are unable to test the pottery or otherwise determine that it is from a reliable manufacturer, consider not using it for cooking, serving, or storing food or drinks.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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35
No washing or boiling removes lead
“Be aware that no amount of washing, boiling, or other process can remove lead from pottery.”
U.S. Food and Drug Administration · Questions and answers on lead-glazed traditional pottery · read on October 26, 2026
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36
If the crock has chips or cracks, use another container
“If the crock has chips or cracks, use another type of container.”
Washington State University Extension, Lewis County · Sauerkraut Making · read on October 26, 2026
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37
Deep scratches and chips can harbor bacteria
“Any food container chosen should be easy to clean and free from deep scratches, chips, or pits that can harbor harmful bacteria or affect the fermentation.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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38
Crock, plate and jars washed in hot soapy water and rinsed well
“The fermentation container, plate, and jars must be washed in hot sudsy water, and rinsed well with very hot water before use.”
National Center for Home Food Preservation (USDA, University of Georgia) · Suitable Containers, Covers, and Weights for Fermenting Food · read on October 26, 2026
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39
Wood is hard to keep clean
“Wooden containers have been used to ferment vegetables but can be difficult to keep clean and sanitary.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026
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40
Metal, other than high-grade stainless steel, degrades
“Metal — except for high-grade commercial stainless steel — can degrade and pit, so is usually not recommended.”
Virginia Cooperative Extension (Virginia Tech) · Vegetable fermentation (FST-328, reviewed 2025) · read on October 26, 2026