Every lacto-fermentation project — sauerkraut, pickles, hot sauce, kimchi, fermented salsa — shares the same critical requirement: keep vegetables submerged below the brine. The moment something pokes above the liquid line, it's exposed to oxygen, and that's where kahm yeast and mold set up shop.
Fermentation weights solve this problem. They're specifically designed to sit inside your jar and hold vegetables below the surface of the brine without introducing contamination or reacting with the acidic environment. If you ferment more than occasionally, they're worth having. This guide covers why they matter, what to look for, and which options are worth buying.
Why Keeping Vegetables Submerged Matters
Lactic acid fermentation is an anaerobic process — it works without oxygen. The beneficial bacteria (Lactobacillus species) that drive fermentation thrive in the oxygen-free environment below the brine. The brine itself becomes increasingly acidic as fermentation proceeds, which inhibits spoilage organisms.
Any vegetable matter above the brine line is in a fundamentally different environment. It has access to oxygen and isn't protected by the acidic brine. This is where kahm yeast grows as a white film, and in worse cases, where mold takes hold. Kahm yeast is harmless but annoying; mold means discarding the batch.
Keeping everything submerged isn't just about safety — it also produces a more consistent ferment. When vegetables bob around and spend time above and below the brine line, fermentation proceeds unevenly, which affects texture and flavor.
What to Look for in a Fermentation Weight
Material. Glass is the gold standard. It's inert, doesn't react with acidic brine, easy to clean, and durable. Food-grade ceramic is also excellent for the same reasons. Avoid plastic if you can — even food-safe plastic can absorb flavors over time, and some plastics can leach trace compounds in acidic environments. Never use metal, which will corrode in brine.
Fit. A weight only works if it actually keeps vegetables submerged. The fit inside your jar matters: a weight that's too small will allow vegetables to float around it. Most commercially available glass weights are designed to fit standard wide-mouth mason jar sizes (wide-mouth quart and half-gallon). If you're using different jars, measure before buying.
Ease of cleaning. Weights go into acidic brine and contact vegetable material. You need to be able to clean them thoroughly between uses. Smooth glass discs are easiest. Weights with complex shapes or crevices are harder to clean reliably.
Grip or handle. Retrieving a smooth glass disc from a narrow jar full of brine is harder than it sounds. Some weights have a small handle, grip ring, or raised edge that makes it easier to remove them cleanly. This is a small quality-of-life feature but worth considering if you ferment frequently.
Best Glass Fermentation Weights
Ball Wide Mouth Pickle Pebbles. Made by Ball (the mason jar company), these glass disc weights are designed specifically for wide-mouth mason jars. They come in packs of two, are perfectly sized for quart jars, and are completely inert and dishwasher-safe. The fit is excellent — they sit flush against the jar walls and don't allow vegetables to float past them. These are the most commonly recommended beginner weight for good reason: reliable, inexpensive, and from a brand built around the mason jar ecosystem. Available on Amazon or at most kitchen supply stores.
Masontops Glass Weights. A slightly thicker glass disc with a small raised grip on top that makes removal easier. They fit wide-mouth mason jars well and are a popular choice for people who ferment regularly. The thicker profile gives them a bit more weight, which helps with lighter, more buoyant vegetables like shredded cabbage. Find them on Amazon.
Ohio Stoneware Crock Weights. If you ferment in a traditional ceramic crock rather than mason jars, you need a different solution. Ohio Stoneware makes ceramic weight plates sized to fit their crocks, which sit inside and hold the entire ferment below the brine. These work in conjunction with a water-seal lid system common to traditional European-style fermentation crocks. Check Amazon or specialty kitchen stores for availability.
Beyond Weights: Complete Fermentation Lid Systems
Some fermenters prefer a system approach — an airlock lid that fits a mason jar and allows CO₂ to escape while keeping oxygen out, combined with a weight. These solve two problems at once: submersion and gas management. Popular options include the Masontops Complete Kit and the Fermentation Lids by Humble House.
For a full rundown of fermentation vessels, lids, and accessories, see our guide on the best jars for fermentation. For gift ideas that include weights and full setups, check out our fermentation gifts under $50 roundup.
Free DIY Alternatives
You don't need to spend money to keep vegetables submerged. These approaches work well, especially when you're just getting started:
The brine-filled bag method. Fill a small zip-lock bag partway with brine (not water — if it leaks, you don't want plain water diluting your ferment). Press it on top of the vegetables to hold them down. It conforms to the shape of the jar and works with any vessel. This is the most common improvised solution and genuinely reliable.
A smaller jar as a weight. A 4-oz mason jar filled with water fits inside a wide-mouth quart jar and sits on top of the vegetables. Simple, free, and easy to clean.
A large outer cabbage leaf. When making sauerkraut or kimchi, lay a whole outer cabbage leaf over the shredded cabbage before adding brine. The leaf helps keep the shredded pieces below the surface and is easy to remove during the process. Not as reliable as a solid weight but works as a supplementary barrier.
A smooth river stone. Washed and boiled clean, an appropriately sized smooth stone can serve as a fermentation weight in a pinch. Use only smooth stones with no porous surfaces that could harbor bacteria. This is decidedly old-school but effective — people fermented vegetables with stones long before glass disc weights existed.
The real job of a fermentation weight.
The weight isn't doing heavy lifting — it's just keeping vegetables down. You don't need something massive. What you need is something that fits your jar, stays in place, and doesn't contaminate your ferment. Even a zip-lock bag of brine achieves that. Buy dedicated weights when you're fermenting regularly and want to simplify cleanup — not because they produce better ferments.
How to Use Your Fermentation Weights
Using a weight correctly is straightforward:
- Pack your vegetables into the jar as directed in your recipe. For sauerkraut, massage with salt first until brine releases. For whole or sliced vegetables, pack them snugly enough that they don't float freely.
- Add your brine until everything is covered.
- Place the fermentation weight on top of the vegetables, pressing gently so they go below the brine surface.
- Check that the weight itself is submerged or sitting just at the brine line. If the weight is above the brine, add more brine to cover.
- Cover the jar and ferment as directed.
Check the jar daily for the first few days. Vegetables can expand as gases form during fermentation, which can push them above the weight. Press them back down and add brine if necessary. For more guidance on what to watch for during fermentation, see our post on identifying and dealing with kahm yeast and our broader guide on how to store fermented foods once fermentation is complete.
Caring for Glass Weights
Glass fermentation weights are low-maintenance:
- Rinse immediately after use to prevent brine residue from drying and becoming harder to remove
- Wash with hot water and dish soap or run through the dishwasher
- Inspect for chips or cracks before each use — a cracked glass weight can contaminate your ferment and is a safety hazard. Replace if damaged.
- Store dry — residual moisture on a stored weight is fine, but store in a clean, dry environment
With basic care, glass fermentation weights last indefinitely. The small upfront investment pays for itself quickly if you ferment regularly — a single weight can be reused across hundreds of batches over years of use.
