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Ultimate Cover Guide: Why Cheesecloth is a No-Go!

When it comes to brewing kombucha, one of the most critical aspects is choosing the right cover for your ferment. While it might be tempting to reach for a cheesecloth or a reusable cloth cover, these options are far from ideal. In this article, we go into the science of why some commonly used materials are insufficient -- and introduce you to the best alternatives for a safe and successful kombucha brew.

The Importance of Covers in Kombucha Brewing

When brewing a batch of booch, one of the essential steps is covering your fermentation vessel properly. The cover serves a triplicate purpose: it allows the necessary gases to escape (preventing pressure buildup), it allows the brew to breathe, and it prevents contaminants like mold spores, bacteria, bugs, and foreign particles from entering (and potentially spoiling) your brew.

It's a safeguard against unwanted intruders that can not only ruin the taste but potentially create a health hazard. Moreover, a good cover facilitates the right balance between aerobic and anaerobic fermentation phases, which is crucial to achieving that perfect brew.  It's also imperative to understand that yeast and mold spores are literally in every breath we take -- so every time you open your brew, you are exposing it to foreigners. 

Pro tip: brews can often change over time as foreigners get introduced.  Key indicators are a change in color of new scobys -- or a change in taste, color, look, or smell of your overall ferment.  If your booch isn't quite what it used to be, the easiest solution is to just grab a new scoby to get you back on track.

But don't worry, the force within the booch is strong, and the bacteria and yeast in quality cultures like Gaia are wild strains anyway that work as a team to mercilessly eliminate foreign invaders (while ensuring ensuring proper pH also works the biology to your favor).  The problem generally comes when it gets overwhelmed by invasion -- often due to incorrect (too low) temps or improper covering. 

Now, let's delve deeper into the breathing needs of kombucha and explore the best options for covers, including a brewery-approved method.

Kombucha's Breathing Needs: Not as Much as You Think

A common misconception in the kombucha brewing community is the exaggerated need for the brew to "breathe." While it's true that kombucha undergoes a phase of aerobic fermentation, where oxygen is utilized by yeast (and some bacteria) to ferment the sugars into alcohol acids and trace alcohol, it also goes through a significant anaerobic phase. This is because kombucha has lots of different varieties of yeast and bacteria.

During the anaerobic processes, the bacteria convert the alcohol and sugar into healthy organic acids in a closed environment, without the need of oxygen.  Think about how the scoby forms on top of the brew, protecting it and sealing it up.  Now think about trying to blow through it.  It's not very breathable, right?

Kombucha doesn't require as much air exchange as one might assume.  It's essential to strike a balance that facilitates both aerobic and anaerobic fermentation without exposing the brew to potential contaminants.

The Science Behind the Cover (& Why NEVER to Use Cheesecloth)

To understand why cheesecloth, muslin, and reusable cloth covers are not suitable, we need to explore the size of mold and yeast spores and the potential for contamination from other particulates.

  • Mold and Yeast Spore Sizes: Mold spores can range from 3 to 40 microns in size, while yeast spores are generally between 1 and 5 microns.
  • Cheesecloth Pore Size: The pores in a cheesecloth can vary significantly, but they are generally much larger than the size of mold and yeast spores, allowing these unwanted guests easy access to your brew.

The Downside of Reusable Cloth Covers

While reusable cloth covers might seem like a more sustainable choice, they come with their own set of problems:

  • Harboring Contaminants: Over time, cloth covers can harbor bacteria, mold, and yeast spores, creating a breeding ground for contamination.
  • Inconsistent Pore Size: Cloth covers have inconsistent pore sizes, which can allow larger particles, including dust and insect debris, to enter your brew.
  • Maintenance: Reusable cloth covers require regular washing and, ideally, sterilization to remain safe, adding to the labor and complexity of your brewing process.

Point being: if you ever run across a kombucha company trying to sell you an overpriced pretty cloth cover, they are either ill-informed, dishonest, or both.  And you should probably run the other way.  We're looking at you, Hannah Crum. 👀

The Superior Alternatives

Understanding the limitations of cheesecloths and reusable cloth covers brings us to more reliable alternatives: coffee filters and paper towels.

  • Coffee Filters:
    • Disposable: Being a one-time-use option, paper towels prevent the accumulation of contaminants, offering a fresh, clean cover with each use.  All without much of a tax on mother nature.
    • Food-Grade: We get it, the covering isn't supposed to touch the brew.  But this is a food application.  When you have a better option AND it's food grade, you should probably use it.
    • Fine Pore Size: Coffee filters have a fine pore size, more effectively keeping out mold and yeast spores while still allowing your kombucha to breathe.  
    • Aerobic and Anaerobic Fermentation: Kombucha undergoes both aerobic and anaerobic fermentation, meaning it requires some air but not much. Coffee filters strike the right balance, permitting a limited air exchange that supports healthy fermentation without letting in contaminants.

  • Paper Towels (in a pinch)
    • Better Pore Size: While not as fine as coffee filters, paper towels still offer a more controlled pore size compared to cloth materials, providing a safer barrier against potential contaminants.  In a pinch, they'll do -- use two.

  • Ultra-Fine Poly Mesh
    • Ultra-Fine Pore Size: the right poly mesh features an ultra-fine pore size, creating a needed barrier.
    • Reusable, Food-Grade, and Easy to Sanitize: Being made of a material that is easy to clean (and food-grade), poly mesh stands as the only reusable option that you would want to consider. It can be sanitized between uses simply with hot water (180°+F water or peracetic acid wash), maintaining a hygienic brewing environment over time.
    • Economical and Eco-Friendly: Given its reusable nature, opting for a poly mesh not only saves you money over time but also reduces waste, making it a green choice for regular brewers.
    • Professional Brewery Standard: Leveraging a poly mesh brings a piece of the professional brewery setup to your home, helping you adhere to high standards of brewing, just like the experts do.

Coffee Filters + Ultra-Fine Mesh: A Brewery-Approved Option

At our brewery, we have found that a combination of a coffee filter and an ultra-fine mesh make your brew essentially impervious. The ultra-fine mesh acts as a formidable barrier, and when used in conjunction with a coffee filter, it creates an optimal environment that supports both phases of fermentation while keeping contaminants at bay. This duo offers a robust solution, providing the necessary breathability while maintaining a sanitary brewing environment, steering you towards brewery quality booch, every time. It's a tried and tested method, bringing professional brewery standards right into your home brewing setup.

But remember, if you're only going to choose one, a coffee filter is the way.


In the intricate dance of brewing kombucha, ensuring the purity of your ferment is paramount. While cheesecloths and reusable cloth covers might be readily available, their use can jeopardize the quality and safety of your brew.

Opting for a coffee filter as your kombucha cover not only offers superior protection against contaminants but also fosters the right environment for both aerobic and anaerobic fermentation processes to flourish.  And adding a fine mesh makes it all the better.

The next time you set out to brew, keep in mind that the right cover can make all the difference -- so choose wisely.  And remember, if you want to brew like a pro, consistency, a heat mat, pH strips, and a proper brew log are a must.

Happy brewing, booches!


  • Raw Brewing Co.

    Hey there Valerie, there’s lots of sizes of coffee filters — we use them on stuff pushing 18 inches wide or more. We will carry them at some point for an easy source, but they’re relatively easily available.

  • Valerie Lillie

    Yikes, I had no idea. I have a 2.5 gallon with a wide mouth. I don’t think there is a coffee filter that would fit. I currently use a black cloth secured with rubber bands and hadn’t thought about the prospect of contamination each time I remove it (which isn’t often – even so…). Okay, so a poly mesh it is. Thank you for sharing this very important information.

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