Fermenting big: from a jar to a 20-liter crock
Salt scales exactly; what changes is the container, the weight, the headspace and how you spread the salt. Everything you need to go from 2 pounds of cabbage to 25.
8 min read Getting good Reviewed October 27, 2026 44 facts, each with its source
When to make the jump
Start with a jar. There's less chance of failure with smaller amounts1, and a mistake costs you 2 pounds of cabbage, not 25. Once your sauerkraut has turned out well a couple of times, a crock makes sense: the NCHFP, the USDA-backed National Center for Home Food Preservation, accepts fermenting it in jars, but warns that it spoils more often that way2.
Salt, temperature and time are the same as in a jar. Four things change: the container, how you spread the salt, the weight and the headspace.
Which container
The rule is a 1-gallon (4-liter) container for every 5 pounds (2.3 kg) of vegetables. A 5-gallon (19- to 20-liter) crock is the ideal size for about 25 pounds (11 kg) of cabbage or cucumbers3.
| Material | Does it work? |
|---|---|
| A food-safe stoneware crock, or glass | Yes, it's the usual choice4 |
| Food-grade plastic | Yes, a good stand-in for a stoneware crock5 |
| High-grade stainless steel | Yes6 |
| Copper, iron, galvanized metal or lead-glazed crocks | No7 |
| Aluminum or brass | No8 |
| Garbage cans or scrub buckets | No: they aren't food-grade9 |
Whatever it's made of, it has to be food-grade, in good repair, free of scratches, chips or cracks, and suited to acid10. Check it for cracks before every use11. Be careful with antique, handmade or decorative crocks: some glazes aren't acid-safe and can leach heavy metals12. The guide Fermentation crocks explains how to tell whether a crock can be trusted. If you're unsure about a plastic, read the label or ask the manufacturer13.
Before you start, wash the crock, the plate and the jars in hot sudsy water, and rinse them with very hot water14.
Salt scales exactly
The NCHFP sauerkraut recipe calls for 25 pounds of cabbage and 3/4 cup of salt15. But a cup of salt weighs 230 to 335 g depending on the salt16: in a crock, that's close to 80 g of difference. That's why Fervida gives salt in grams, at 2.5%: 25 g per kilo17. The percentage doesn't change with size. Twice the cabbage takes twice the salt, always weighed18. Never less than the recipe calls for19.
| Shredded cabbage | Salt at 2.5% |
|---|---|
| 2.3 kg (5 lb), one batch | 57.5 g |
| 5 kg (11 lb) | 125 g |
| 10 kg (22 lb) | 250 g |
| 11.3 kg (25 lb), the NCHFP recipe | 282.5 g |
Try it with your cabbage
Dry-salted
In rangeAt 2.5%, within the range the guides use.
Salt in batches. Don't try to mix 25 pounds at once. The NCHFP works with about 5 pounds at a time20: shred that batch, add its salt and mix it well with clean hands21. Press it into the crock and move on to the next one. Weigh each batch's salt for what that batch weighs. That way it reaches all the cabbage evenly: salt that's measured wrong or spread unevenly is one of the causes of soft sauerkraut22.
The weight and the cover
All the cabbage has to stay 1 to 2 inches (2.5 to 5 cm) under the brine23. In a crock there are two ways to hold it down:
- A plate slightly smaller than the opening, but large enough to cover most of the cabbage24, with 2 or 3 sealed quart jars filled with water on top25. In a 20-liter bucket, a snug-fitting plate works26.
- A large sealed bag with 3 quarts (about 3 liters) of brine at about 28 g of salt per liter27. For a 5-gallon crock, turkey freezer bags work28. Only food-grade plastic, never garbage bags29.
The edges are the weak spot: that's where mold shows up when the cover isn't held down well30. Cover the crock with a clean, heavy towel, which keeps out insects and molds31. With a brine bag, don't disturb the crock until the bubbling stops32; with jars as weights, check it 2 to 3 times a week and skim off any film33.
Headspace
A crock isn't filled to the top. The NCHFP wants the rim at least 4 to 5 inches (10 to 13 cm) above the cabbage34, and University of Minnesota Extension says about 75% full35. For kimchi, Colorado State says two-thirds, because it bubbles and rises36. Fervida asks you to leave at least 30% of the crock empty, between Minnesota's quarter and Colorado's third: that is a house rule.
The gallon rule makes the numbers work. The NCHFP's 25 pounds of cabbage make about 9 quarts of sauerkraut37, and a 5-gallon crock leaves room for the plate, the weight and the brine that rises in the first days.
Temperature
The figures are a jar's: at 21–24 °C (70–75 °F), sauerkraut takes 3 to 4 weeks; at 16–18 °C (60–65 °F), 5 to 638. Below 16 °C (60 °F) it may not ferment, and above 24 °C (75 °F) it softens39.
Pick the spot before you fill the crock: full, with the cabbage, the brine and the weight, it can top 20 kg (45 lb), and you won't be moving it. Make it cool, steady and dark, because lactic acid bacteria are sensitive to light40. A thermometer next to it tells you the air temperature41; for the cabbage's, tape the probe to the side of the crock, as the guide Fermentation chambers explains. In summer, find the coolest corner of the house and check the crock more often42.
Packing it into jars
A 5-gallon crock won't fit in the fridge. When the sauerkraut is done, by the signs in the sauerkraut guide, pack it into clean jars, pressed down under its juice, and close them. In the fridge, tightly covered, it keeps for several months43. Without a heat treatment it keeps fermenting in the jars44: get them into the fridge the same day and leave a finger's width free at the top.
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.
-
1
There's less chance of failure with smaller amounts
“there is less chance of failure when smaller amounts are made.”
Washington State University Extension, Lewis County · Sauerkraut Making · read on October 26, 2026
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2
Jars are acceptable, but spoil more often
“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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3
1 gallon per 5 pounds of vegetables: a 5-gallon crock for 25 pounds of cabbage
“A 1-gallon container is needed for each 5 pounds of fresh vegetables. Therefore, 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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4
Glass and stone crocks are common and well suited
“Glass and stone crocks are common and generally well suited.”
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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5
Food-grade plastic and glass are good stand-ins for a stoneware 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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6
High-grade stainless steel can be used
“High-grade, commercial stainless steel can be used”
University of Illinois Extension · Fermentation handout (2020) · read on October 20, 2026
-
7
No copper, iron, galvanized metal or 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
-
8
No aluminum or brass either
“Do not use aluminum, copper, brass, galvanized, or iron containers for fermenting pickles or sauerkraut.”
Clemson Cooperative Extension, Home & Garden Information Center · Common Pickle Problems (HGIC 3101, revised August 2020) · read on October 26, 2026
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9
Garbage cans and scrub buckets aren't food-grade
“Do not use garbage cans or plastic "scrub" buckets. These containers are not food grade and will produce unsafe or off-flavored sauerkraut.”
Washington State University Extension, Lewis County · Sauerkraut Making · read on October 26, 2026
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10
Food-grade, in good repair, free of scratches, chips or cracks, and suited to acid
“Containers should be food-grade, in good repair, free of scratches, chips or cracks, and appropriate for acidic conditions.”
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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11
Check the container for cracks before use
“Before use, inspect the container for cracks.”
University of Minnesota Extension · Preserving food at home: Fermentation (reviewed 2026) · read on October 25, 2026
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12
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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13
If you're unsure about a plastic, read the label or ask the maker
“If you’re not sure if a plastic container is safe for food, read its label or contact its manufacturer.”
Clemson Cooperative Extension, Home & Garden Information Center · Common Pickle Problems (HGIC 3101, revised August 2020) · read on October 26, 2026
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14
Crock, plate and jars washed in hot sudsy water and rinsed with very hot water
“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
-
15
25 pounds of cabbage with 3/4 cup of salt
“25 lbs cabbage 3/4 cup canning or pickling salt”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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16
A cup of salt weighs 230 to 335 g depending on the salt
“Salt varies from 230 g to 335 g per US cup measured.”
UC Master Food Preservers, Inyo-Mono · Brine Math Made Easy · read on October 20, 2026
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17
25 g of salt per kilo, 2.5%
“2.5% 25 g / kg food”
UC Master Food Preservers, Inyo-Mono · Brine Math Made Easy · read on October 20, 2026
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18
It's best to weigh the salt
“It is best to weigh salt for accuracy.”
University of Illinois Extension · Fermentation handout (2020) · read on October 20, 2026
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19
Don't make sauerkraut with less salt than the recipe calls for
“Caution: Do not attempt to make sauerkraut or fermented pickles by cutting back on the salt required.”
National Center for Home Food Preservation (USDA, University of Georgia) · General Information on Fermenting · read on October 26, 2026
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20
Work with about 5 pounds of cabbage at a time
“Work with about 5 pounds of cabbage at a time.”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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21
Each batch with its salt, mixed well with clean hands
“and add 3 tablespoons of salt. Mix thoroughly, using clean hands.”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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22
Inaccurate or uneven salt makes soft sauerkraut
“Insufficient salt (inaccurate measuring or uneven salt distribution.)”
Washington State University Extension, Lewis County · Sauerkraut Making · read on October 26, 2026
-
23
1 to 2 inches under the brine
“Cabbage and cucumbers must be kept 1 to 2 inches under brine while fermenting.”
National Center for Home Food Preservation (USDA, University of Georgia) · Suitable Containers, Covers, and Weights for Fermenting Food · read on October 26, 2026
-
24
A plate slightly smaller than the opening that covers most of the cabbage
“The plate must be slightly smaller than the container opening, yet large enough to cover most of the shredded 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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25
On top, 2 or 3 sealed quart jars filled with water
“To keep the plate under the brine, weight it down with 2 to 3 sealed quart jars filled with water.”
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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26
In a 20-liter bucket, a snug-fitting plate
“In larger vats, pickles are weighted down with wood over plastic, another acceptable method would be to use a snug-fitting plate in a 20 L (5 gal) plastic bucket.”
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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27
Or a large sealed bag with 3 quarts of brine
“Fine quality fermented vegetables are also obtained when the plate is weighted down with a very large clean, plastic bag filled with 3 quarts of water containing 4-1/2 tablespoons of salt. Be sure to seal the plastic bag.”
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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28
For a 5-gallon crock, turkey freezer bags
“Freezer bags sold for packaging turkeys are suitable for use with 5-gallon containers.”
National Center for Home Food Preservation (USDA, University of Georgia) · Suitable Containers, Covers, and Weights for Fermenting Food · read on October 26, 2026
-
29
Only food-grade plastic; never garbage bags
“Caution: Be certain that foods contact only food-grade plastics. Do not use garbage bags or trash liners.”
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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30
Mold shows at the edges when the cover isn't held down
“mould is clearly visible at the edge of a crock fermentation where plastic has not properly been weighted down over the brine.”
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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31
A clean, heavy towel keeps out insects and molds
“Covering the container opening with a clean, heavy bath towel helps to prevent contamination from insects and molds while the vegetables are fermenting.”
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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32
With a brine bag, don't disturb it 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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33
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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34
The rim at least 4 to 5 inches above the cabbage
“Be sure it is deep enough so that its rim is at least 4 or 5 inches above the cabbage.”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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35
In a crock, 4 to 5 inches of headspace: about 75% full
“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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36
Kimchi, two-thirds full, because it bubbles
“Fill container about 2/3 of the way full, as fermenting microorganisms will release carbon dioxide (CO2) and create bubbling and fizzing.”
Colorado State University Extension · Understanding and Making Kimchi (2025) · read on October 20, 2026
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37
The NCHFP recipe makes about 9 quarts of sauerkraut
“Yield: About 9 quarts”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
-
38
3 to 4 weeks at 70–75 °F; 5 to 6 at 60–65 °F
“At temperatures between 70º and 75ºF, kraut will be fully fermented in about 3 to 4 weeks; at 60º to 65ºF, fermentation may take 5 to 6 weeks.”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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39
Below 60 °F it may not ferment; above 75 °F it softens
“At temperatures lower than 60ºF, kraut may not ferment. Above 75ºF, kraut may become soft.”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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40
In the dark: lactic acid bacteria are sensitive to light
“Containers with fermenting produce should be stored in a dark place, as Lactobacillus are sensitive to light.”
University of Minnesota Extension · Preserving food at home: Fermentation (reviewed 2026) · read on October 25, 2026
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41
A thermometer measures the air temperature
“You can use a thermometer to measure air temperature.”
University of Minnesota Extension · Preserving food at home: Fermentation (reviewed 2026) · read on October 25, 2026
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42
In summer, a cool spot and frequent checks
“Look for a cool place in your home and when fermenting in the summer, plan to check your ferments often for doneness.”
K-State Research and Extension (Kansas State University) · Taking a New Look at Fermented Foods (MF3491, June 2020) · read on October 20, 2026
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43
Once fermented, it keeps for months in the fridge, tightly covered
“Fully fermented kraut may be kept tightly covered in the refrigerator for several months”
National Center for Home Food Preservation (USDA, University of Georgia) · Sauerkraut · read on October 20, 2026
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44
Repacked without heat, it keeps fermenting
“If fermented vegetables are re-packaged into secondary containers without any pasteurization or heat treatment, the fermentation will continue.”
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