Do I need an airlock or weights to ferment peppers?

You need a weight, or some other way to keep every piece of pepper under liquid, far more than you need an airlock. Solids above the brine are where mold starts. An airlock is the easiest way to let gas out while keeping air from coming in, and Illinois Extension recommends one, but it also says fermenting is possible without one as long as the vegetables stay submerged [1]. A loosely screwed lid that you check, or a tight lid you open every day or two to release gas, also works. This page compares the lid and weight options, the vessels that are safe to use, and how full to fill them.

Three jobs your setup has to do

Every fermenting setup, from a mason jar to a 50-gallon barrel, has three jobs:

1. Keep the food under liquid. Molds and film yeasts need oxygen, so they grow at the surface where food or brine meets air. UC Davis food scientists advise keeping all produce under the brine, using weights if needed [2].
2. Let gas out. Lactic acid bacteria and yeasts make carbon dioxide, most of it in the first week. In an airtight container that gas can break the vessel [3].
3. Keep air from getting back in. UC Davis advises a firmly fitted lid with no air gaps, releasing carbon dioxide by opening the container from time to time or by using an airlock [2].

An airlock handles jobs 2 and 3 by itself. A weight handles job 1. Neither one replaces the other.

Lid options compared

Commercial vegetable fermenters in Europe usually use a sealed vessel with a one-way valve for gas, according to Ireland's food safety authority [4]. That is the same principle as an airlock lid on a jar.

UVM Extension's sauerkraut method uses a plastic lid screwed on loosely and sets the jar in a bowl to catch overflow [5]. That simple setup is a reasonable start for a first pepper ferment.

Ways to hold the peppers down

Glass fermentation weights. Heavy glass discs sized to fit inside a wide-mouth jar. They do not react with acid and are easy to clean. A chipped weight should be replaced.

A smaller jar or a sealed bag of water. USDA's home canning guide describes covering the vegetables with a plate slightly smaller than the container opening and weighting it with two or three sealed quart jars filled with water [6]. In a mason jar, a small jelly jar pressed into the mouth does the same job.

A bag of brine. USDA's guide also describes a large food-safe plastic bag filled with 3 quarts of water containing 4½ tablespoons of canning or pickling salt, sealed and laid on top [6]. The bag conforms to the surface and seals the edges. Because it holds brine instead of plain water, a leak does not weaken your ferment. The guide notes a brine-weighted crock does not need to be disturbed until bubbling stops [6].

Pepper or cabbage leaves, or parchment. Some makers press a few whole pepper pieces, a cabbage leaf or a round of parchment onto the surface of a mash before adding the weight. They catch floating bits. They are not a weight by themselves.

What not to use. Avoid metal weights. UVM advises against metal for this job [5], and USDA's troubleshooting table says pickles made with brass, copper or zinc utensils should not be used at all [7]. Rocks from outside and anything you cannot sanitize do not belong in a ferment.

Vessels that are safe for acid ferments

Snyder and coauthors, writing for small fermented food businesses, call for food-grade fermentation vessels [9]. Clean and sanitize any vessel before you pack it.

How full to fill the vessel

Fermenting food expands. Gas lifts a mash, brine rises and bubbles over, and a jar packed to the top can push liquid and pepper through the airlock and onto the counter.

• Capacity. USDA's home canning guide and Illinois Extension both allow 1 gallon of container for every 5 pounds of fresh produce [6] [1]. That is about 1.7 liters per kilogram, so a quart jar holds a bit over a pound of mash with room to rise, and a half-gallon jar holds about 1 kilogram.
• Depth of brine. USDA's guide keeps fermenting vegetables 1 to 2 inches under brine [6]. In a mash, aim for at least a thin layer of liquid over the solids once you press it down.
• Room above. In a jar, leave a few inches of empty space between the top of the weight and the lid during the first week, when gas production is highest. A jar that is half to two-thirds full is easier to manage than one that is nearly full. A maker on The Hot Pepper forum noted in 2014 that a half-full jar had more air above the ferment and suggested more salt to compensate [10]; a weight that seals the surface solves the same problem.
• A tray underneath. Set the jar on a plate or in a bowl for the first week [5].

Once active fermentation slows, after about the first week, the mash settles and overflow stops. If you moved from a loose lid to a tighter one, keep releasing gas until the ferment is fully finished.

Choosing a setup and getting started

For a first pepper ferment, a wide-mouth glass jar, a glass weight or small jar, and an airlock lid or a loosely fitted plastic lid will do everything you need. The full method with weights and timing is on how to ferment peppers, step by step. If something grows on the surface anyway, kahm yeast or mold explains what it is and whether to keep the batch.

References

1. University of Illinois Extension, Fermenting FAQ, undated, accessed October 2026. https://extension.illinois.edu/food-preservation/fermenting-faq
2. DiCaprio E, Marco M, Finnegan P, Hanlon M, Common issues with fermented fruits and vegetables, UC Davis and UC ANR, version 1.0, March 15, 2022. https://ucfoodsafety.ucdavis.edu/sites/g/files/dgvnsk7366/files/media/documents/Troubleshooting%20fermented%20fruits%20and%20vegetables%20FINAL.pdf
3. DiCaprio E, Marco ML, Kim H, Ting KC, Safely Ferment Fruits and Vegetables at Home, UC Davis, version 1.0, March 15, 2022. https://eatlac.ucdavis.edu/sites/g/files/dgvnsk13106/files/media/documents/Safely%20Fermented%20Fruit%20and%20Vegetable%20Factsheet.pdf
4. Food Safety Authority of Ireland, Guidance Note 37: Good Manufacturing Practices for the Production of Ready-to-eat Unpasteurised Fermented Plant-based Products, 2021 (marked draft). https://www.fsai.ie/getmedia/f8ba3e7e-d7aa-4771-86c3-8d65aa8a038c/GN-37-Good-manufacturing-practices-for-the-production-of-ready-to-eat-unpasteurised-fermented-plant-based-products(1).pdf?ext=.pdf
5. Amsden J, Sauerkraut: DIY Fabulous Fermented Food, UVM Extension, August 11, 2021. https://www.uvm.edu/extension/news/sauerkraut-diy-fabulous-fermented-food
6. USDA and National Center for Home Food Preservation, Complete Guide to Home Canning, Guide 6: Preparing and Canning Fermented Foods and Pickled Vegetables, revised 2015. https://nchfp.uga.edu/papers/guide/GUIDE06_HomeCan_rev0715.pdf
7. National Center for Home Food Preservation, Causes and Possible Solutions for Problems with Fermented Pickles, adapted from So Easy to Preserve, 6th ed., 2014 (reviewed 2020). https://nchfp.uga.edu/how/ferment/general-information-on-fermenting/causes-and-possible-solutions-for-problems-with-fermented-pickles/
8. Virginia Cooperative Extension, Enhancing the Safety of Locally Prepared Foods: What do I need to know to sell Fermented Vegetables at the farmers market? FST-308NP, 2019. https://ps.spes.vt.edu/producers/documents/FST-308.pdf
9. Snyder A, Breidt F, Andress EL, Ingham BH, Manufacture of Traditionally Fermented Vegetable Products: Best Practice for Small Businesses and Retail Food Establishments, Food Protection Trends 40(4):251-263, 2020. https://www.ars.usda.gov/ARSUserFiles/60702500/Fermented%20Veg%20Manuscripts/p437.pdf
10. The Hot Pepper forum, Fermenting peppers, 10% salt too much? (thread, page 2), September 2014. https://thehotpepper.com/threads/fermenting-peppers-10-salt-too-much.50031/page-2