Mason Jar Fermenting Weights–A Comparison

I saw a friend use a water-filled plastic baggy as a weight in her ferment. I was concerned. I mean, what if the baggy leaked? Or, worse yet, plastic from the baggy leached into her ferment? Sarah addresses this very topic in this post. For more comparison of the best fermenting weights for mason jars, keep reading.

All ferments require some type of weight at the top of the jar or crock. And, while you can substitute a weight when you are just starting, it is better to get a dedicated fermenting weight to remove all chance of floating, or contamination.

The weight keeps your ferment below the level of the brine. This prevents mold, fungal, and yeast colonization and contamination on the surface of the acidic ferment. If necessary, a clean piece of plastic, a rock, or even a plate can be substituted for a non-reactive glass weight temporarily, if you are ill or traveling and don’t have your Fermentools with you.

Mason Jar Fermenting Weights: The best fermentation weights compared

Pros and Cons of a Glass Weight:

Pros: Glass is non-reactive and non-porous. Despite the often high acidity of ferments, glass will not leach into the ferment. Being non-porous, it can be sterilized with boiling water and will not absorb or carry bacteria between ferments or between the room and your ferment.

Cons: Glass is heavy and may require a particular sized jar. If traveling, jars can be challenging to get or heavy to pack with you. But for the peace of mind of a good ferment weight, it is worth the slight hassle to be careful with packing. If you are fermenting at home, you will have no issues with the glass weight.

Pros and Cons of Other Weight Options:

Plastic Pros and Cons:

A piece of slightly stiff plastic, like the lid of a yogurt container, is easily located and cut to the size of your jar. It can be washed in hot water, but cannot withstand boiling water.

However, plastic leaches, particularly in acidic environments. So, your ferment will have plastic leached into it if plastic is used as the weight. As plastic also cannot be fully sterilized and is slightly porous, using one piece of plastic over multiple ferments could cause transfer of potentially unwanted bacteria or bacterial and fungal contamination.

Plate Pros and Cons:

Usually used on larger fermenting crocks, particularly for sauerkraut, a plate can be a handy weight. Choose a glass plate as opposed to a ceramic plate, particularly if the ceramic has an area that is unglazed. Ceramic is porous and sometimes ceramic glazes can have heavy metal contaminants, which could negatively impact your ferment. A smooth glass plate, that is an exact fit for the top of your crock would be preferable to a ceramic plate, or a plate that did not quite have a close fit.

Rock Pros and Cons:

Rocks are easily located, can be scrubbed and boiled, and are heavy enough to act as weights. However, many rocks are porous and even a thorough boiling and scrubbing may not remove all bacteria from the stone. Second, rocks are nearly always made of a mix of minerals and you do not know whether a particular stone may not contain heavy metals or other compounds that could leach into your ferment. Rocks, particularly in the acidic environment of your ferment, will leach and rocks like limestone could even dissolve.

When looking for a long-term fermenting weight, go with a non-reactive glass weight. It will help keep your ferment happy, and you and your family healthy, for a long time. If you need a short-term solution, use wisdom and remember that acidic environments can leach chemicals and metals from plastic, stone or metal weights.


Because wide-mouthed Mason jars are easy to get, inexpensive, safe for fermenting and come in a variety of sizes, the Fermentools products are made to fit them. Find glass fermentation weights, airlocks, specially designed surgical steel lids and more at the Fermentools store.


Sarah Dalziel is passionate about DIY skills, knowledge, and self-sufficiency. She was homeschooled K-BSc and enjoys questioning, researching, and writing about hands-on skills and preparedness. Ethnobotany, natural dyes, and self-sufficiency fascinate her. If she isn’t writing about them, you’ll find her dipping yarn into a steaming dye pot, or stirring up a batch of woad pigmented soap. Sarah blogs at, a natural dye and fiber skills blog, and also at, an interdisciplinary skills and writing blog.

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