A Trick For Keeping Flies out of Mason Jars While Fermenting (It’s not cheesecloth)

Many of our wild fermentations (a style of fermenting that uses naturally occurring yeast in the air) require the same step – cover the vessel with cheesecloth to allow wild yeasts to enter the jar but keep the flies at bay (if you’re struggling with the terminology surrounding different types of fermentation, check this out).  We use mason jars to do a lot of our fermentation and were looking for an alternative to cheesecloth to cover the ferments in the early stages.

While cheesecloth (or other cloths) work, I find it frustrating.  It ‘feels’ flimsy, ends up as garbage, I often use several pieces before a ferment finishes, a fan can blow it off and I find it looks ugly.  I know these are minor issues but they are things I think about. 

Or thought about.  Because my woes are well behind me now:

A Trick For Keeping Flies out of Mason Jars While Fermenting (Its not cheesecloth) November

A reusable coffee filter is a perfect replacement!

I don’t know how large a yeast molecule is but have been used this a few times and it’s been very successful.  The yeast either easily passes through the filter (which I suspect to be the case) or enters the jar as I lift the filter to stir or smell the contents (in this case, the starter for homemade ginger beer).



  1. I cut out squares of scrap fabric (I get lots of nice squares out of hubby’s threadbare plaid boxers, actually!) and I twist a ring on the jar after the cloth, holding everything securely. With a nice plaid, my fermenting jars look pretty sweet!

  2. If you’re using mason jars (and not larger vessels) you could also try out sprouting lids. Don’t know if you already have some for making sprouts, but the mesh screen would certainly keep bugs out.

  3. @AlchemyPickle says:

    I use cloth napkins and a rubber band, or cut up squares of old sheets or tea towels. They are heavier than cheesecloth, but still allow lots of air flow, and I just throw them in the wash after. Cheesecloth also leaves bits of fluff and thread all over, so I don’t like to cut it up in the kitchen.

  4. I have used a paper coffee filter, with the canning ring to hold it on.

  5. I use a muslin grain bag that you can buy at any brew store. It is stretchy and will fit over any size container.

  6. It works well, they only cost about $.50 and last a while before having to be changed! Lots of breathing room!
    I use it on my kombucha fermenting jar.

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