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Preventing Kahm Yeast and Mold in Fermentation

How to safely remove kahm yeast and mold from fermented vegetables

It happens to all of us. You open a jar of sauerkraut or fermented pickles and there’s something unwanted growing on the top. Don’t worry! Here is everything you need to know about kahm yeast and mold.

  • Is it still safe to eat?
  • What is the difference between kahm yeast and mold?
  • How can you prevent it from happening?

Kahm Yeast

Kahm yeast is a wild-yeast strain that forms a layer that completely covers the top of a ferment. If it’s been left to ferment for a while, it may have trapped air bubbles below the surface.

The picture below is kahm yeast growing over the top of fermented pickles. You can really see how it traps bubbles and forms a complete layer.

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Kahm yeast

Is kahm yeast safe?

While kahm yeast is not ideal, it is not actually harmful. So it is fine to eat a ferment contaminated with kahm yeast.

I most often get it on my ginger beer, hot sauce, and apple cider vinegar.

Here’s how to deal with kahm yeast:

  1. If you find a layer floating on top of your ferment, just skim it off. It is usually pretty easy to remove.
  2. However, the ferment will still be contaminated and the yeast will grow back again and again. So I recommend finishing up the ferment quickly so you don’t have to keep removing yeast.

Mold

Mold is a much bigger concern. It should be pretty obvious when a ferment has mold. It can be blue, green, black, brown, or white. It’s usually fuzzy looking, and unless it’s been there for a long time, it doesn’t cover the entire ferment.

How to safely remove kahm yeast and mold from fermented vegetables
Mold on fermented beets.

When you see mold on top of a ferment it is just the sporing body. Like mushrooms and other fungi, most of the mold filaments (called hyphae) are unseen, below the surface.

There are certain kinds of mold that are perfectly safe to eat. These include cheese, miso, and tempeh. However, the majority of the molds are NOT safe to eat.

Here’s how to deal with mold on a ferment:

  1. If the mold is on sourdough starter, a fermented beverage, or a condiment, then throw it out. The hyphae will have contaminated the entire ferment. It can’t just be scraped off.
  2. The only type of fermentation that is safe to eat after mold contamination is salt-brined ferments. And there are still a few rules:
    • The brine must be at least 2% salt to prevent the hyphae from growing in the liquid. So mold on a lower salt ferment isn’t safe.
    • Remove the mold completely, it usually comes off easily enough. And remove any of the vegetables/fruit/etc. that was floating above the brine as it will be contaminated by the mold.
    • The salt-brine fermented food that remained completely below the brine is safe to eat. I recommend eating the ferment quickly, as the mold usually comes back within a few days of being removed.
    • If eating a mold-contaminated ferment isn’t your thing, it’s fine to dump it into the compost. Never eat a moldy ferment that you are uncertain about. It’s always better to be safe.

Prevention

It is impossible to have a perfect ferment every time, but there is a number of things we can do to ensure that our ferments don’t get contaminated.

  1. Cleanliness: If you’ve had any mold or kahm yeast in your kitchen then make sure that you’ve sanitized all the affected jars and equipment. And be extra clean for the next few months.
  2. Temperature: Mold and yeast both thrive in warm temperatures, so try to ferment at less than 68 F (20 C).
  3. Air-tight ferments: If you don’t have a pickle pipe or fido jar then make sure your vegetables are completely submerged below the brine.
  4. Follow the recipe: Use the right amount of salt in your brine. Keep other types of cultures well-fed and vigorous. And the good bacteria/yeast/fungus will prevent contamination.

Filed Under: General Fermentation InformationTagged With: Kahm Yeast, Mold

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Comments

  1. Mohsin

    July 27, 2020 at 11:16 pm

    Well i started to brew pineapple vinegar now what happen is
    With in 7 days a thick jelly started forming i think so it might
    Be mother of vinegar after that what i did is i filter the pulp and juice and kept this mother with this juice
    Is this correct but i didn’t understand so fast the mother take place
    Also let me know if i see this mother it that mean that my
    Vinegar is ready or i had to wait

    Reply
    • Emillie

      July 28, 2020 at 9:30 am

      Hi, I haven’t made pineapple vinegar, so I don’t know if it has a mother, nor what the mother would look like. I know that pineapple makes stringy, clumping yeast when it’s used in other fermented beverages (kombucha or water kefir). Maybe that is what you are seeing? Good luck!

      Reply
  2. Richard Townshend

    September 5, 2022 at 11:12 am

    I have had success preventing or minimizing kahm yeast by adding a layer of olive oil on top of the fermentation….it’s a good fix and it’s edible!

    Reply
    • Emillie Parrish

      September 6, 2022 at 11:01 am

      Thanks for sharing! I haven’t tried that, but I can see how oil would create an effective oxygen barrier. Cheers!

      Reply
    • Anonymous

      September 26, 2022 at 4:51 pm

      I’ll try it

      Reply
    • Ellen

      November 9, 2022 at 3:38 pm

      I used to cover my ferments with coconut oil that would harden and this also helped the veggies stay below but the one exception to topping with oil of any kind is if you have garlic in the ferment. Apparently, botulism can develop.

      Reply
      • Emillie Parrish

        November 10, 2022 at 8:58 am

        I’ve never tried that. Thanks for sharing!

        Reply
  3. AF

    November 2, 2022 at 11:49 am

    What do you do to remove Kahm yeast in your ACV? Just learn to live with it?

    Reply
    • Emillie Parrish

      November 2, 2022 at 1:40 pm

      Kahm yeast will naturally die as the ferment acidifies. So you don’t need to remove it or worry about it at all. Once it dies you can filter it out of your ACV (when bottling). The pickle photo was taken about 3 weeks ago. This past weekend the yeast was all dead… but I was impatient to eat the pickles so I didn’t take a photo. Cheers! Emillie

      Reply

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