What is Kahm Yeast & Is Kahm Yeast Safe?

As a newbie fermenter, I came across kahm yeast and promptly threw everything out. I wish I knew then what I know now. If you are wondering if your ferment is safe, read on as Colleen explains what it is and what it means.

Posted by Colleen

If you’ve done any fermenting, particularly with vegetables and fruits, you’ve probably come across kahm yeast at one point or another. Kahm is the white film that often covers the top of your ferments. It is sometimes confused for mold. Even though it looks a little funky, it’s not something that is harmful to you or your ferment.

What is Kahm Yeast?

What is Kahm Yeast?

Kahm yeast is not a type of mold, but rather an aerobic yeast that forms when the sugar is used up and the PH of the ferment drops because of the lactic acid formation. Certain vegetables are more prone to getting kahm yeast, particularly if they are sweeter like beets, carrots, and peppers. It tends to form more often on open-air ferments, when the temperature is too warm, or in a low salt brine. While using an airlock on your ferments can decrease the chances of molds forming on the surface because of less contact with oxygen, kahm yeast can still form. The ferment in the picture shown above had an airlock during fermentation – not to worry, everything tasted fine!

Some people prefer to remove the the yeast by skimming the surface of the ferment, but it can be hard to remove all of it, and it will often come right back. I tend to just leave it be, skimming off as much as I can when I’ve decided it’s finished fermenting, right before I put it in the fridge. It will continue to grow in the fridge, but much more slowly.

How to Tell the Difference Between Kahm Yeast and Mold

Kahm yeast is a thin, white to cream-colored layer, sometimes with air bubbles of trapped carbon dioxide. It often has a “stringy,” bloom-like look to it. Mold, on the other hand, is raised and fuzzy and can be white, black, pink, green or blue. Mold most often starts as spots on the surface and then spreads into a thick layer. White mold is usually harmless. You can scrape it off.  But if you have mold of any other color throw the whole thing out. Phickle has written a great article on the difference between mold and kahm yeast here: The Wrath of Kahm: Is it Mold or Kahm Yeast?

Difference between kahm yeast and mold | fermentools

While getting mold on your ferments can be frustrating , it’s something that happens to all of us. Kahm yeast is even more common but is not something that needs to be worried about. If you’re having recurring issues with kahm yeast, try using more salt in your brine or fermenting at cooler temperatures. Make sure that you clean all of your fermenting vessels and tools thoroughly between use. Above all, stay calm and keep on fermenting!


To eliminate the problems associated with oxygen exposure, use airlocks with your ferments. The Fermentools lid is specially made of surgical-grade steel to fit the airlocks perfectly, not rust, and last a lifetime. To get yours, visit the Fermentools store.


Colleen has been foraging for wild food and fermenting for many years. She loves all types of fermenting, including making lacto-fermented veggies, kombucha, kefir, yogurt, and sourdough. She also has a special fondness for brewing hard cider and mead (honey wine). Along with her husband Joel, they grow much of their own food and herbs in a permaculture style garden. She makes and sells handmade herbal salves and lip balms in her Etsy shop, CocosHerbals, and writes about all of her adventures with food, gardening and homesteading at growforagecookferment.com.



  1. Stacey on June 28, 2020 at 8:37 pm

    Thanks for this. I think it’s a mental block. As soon as I see kahm I scrape ut off, put the ferment in the fridge and then Im worried about eating it. I used to immediately throw it out.

    Without a ph testing kit, what are some signs that the ph is around 4?

    I recently had kahm appear on my beet kvass. I used a 3% brine. Do you suggest maybe a 5% next time?

    • Carol Alexander on September 5, 2020 at 9:26 pm

      Hi Stacey,
      Did you see the link in this post to another one on the Phickle blog? She has a few suggestions of things you can try.

      • kwan on February 17, 2021 at 4:01 pm

        Hi Carol,
        I understand that kahm yeast is a result of the sugars being used up in my fermentation. Do you suggest I should add more sugar to prevent this? Will appreciate your advice.. I just started doing food fermentation and experimenting different fermented food.

        • Carol Alexander on February 20, 2021 at 12:55 pm

          I’ve never seen it advised to add sugar to a ferment.

  2. Linda Chandler on August 18, 2020 at 2:48 am

    I have 2 big buckets of watermelon vinegar working. Both have a thin layer of kahm yeast on top. I stir them everyday with my hand an have noticed on only one of them the top inch or so feels a little warm. Is it the yeast producing heat? Why only on one?

    • Carol Alexander on September 3, 2020 at 4:18 pm

      Interesting! That’s what I would say. Or, because it’s near the surface where the room is warm.

    • Kimberly on September 30, 2020 at 12:39 am

      To answer your question, I would need to ask you if the bucket with the yeast growing is the bucket that you put your hand in first?

      I ask this because if so, then maybe that bucket somehow got the spores for the yeast in it from your hand/arm being in there. Just a thought.

      Also, yes, both your ferment and the yeast are exothermic (that means that both produce their own heat). So, if you have yeast growing in one bucket and not the other, then it is likely that the yeast is the factor that is producing the additional heat and making it so noticable to you. Hope these responses help a bit.

      • Carol Alexander on October 10, 2020 at 3:31 pm

        Thanks for those thoughts, Kimberly!

  3. Felix on September 30, 2020 at 7:21 pm

    Are the pics gone?

    • Carol Alexander on October 10, 2020 at 3:33 pm

      Working on fixing that, Felix!

  4. Aileen on October 8, 2020 at 6:33 pm

    I get a white sediment on the bottom of the jar of dill pickle …is that Kahm yeast?? We threw out 42 jars of dills this year because I wasn’t sure if they were still good or not.

    • Carol Alexander on October 10, 2020 at 3:35 pm

      I think kahm is a film that floats, normally. Could that sediment been from your water? I get sediment because I have a lot of minerals in my water.

      • Dee Kay on November 10, 2020 at 1:19 am

        I think Carol’s right, the precipitate at the bottom could be from mineral-rich “hard” water. This also happens when your brining salt has other ingredients in it; double-check the label.

    • Randy on November 4, 2020 at 9:32 pm

      Aileen, that white sediment is probably nothing more than wild yeast that was more active early in the fermentation. It can generate a lot of CO2 gas if there are sugars present. It’s what sometimes makes dill pickles a little fizzy, and I usually consider it a good thing.

    • Jes on November 13, 2020 at 5:09 pm

      I got that with every batch of fermented pickles I did last summer, and none of them had a weird smell or tasted off. I think it must be sediment from the water, but it didn’t alter the flavor of the pickles. Might even be a product of the carbonation interacting with soft plant tissue. Smell is the definitive thing for me: if it smells way too alcoholic or like a full garbage can, I toss it, but if it smells sweet and fresh, I keep it, even if it’s got particles floating at the bottom (as long as there’s no fuzzy mold, obviously).

    • kevin on February 21, 2021 at 7:25 am

      pretty sure white sediment on bottom is normal .the reason I say this is that the living ferment kefir I buy from the shop has white sediment on the bottom of the jar also my homemade kefir and lacto water all have white sediment on bottom which pretty sure is the good stuff cheers

  5. Kerry Crouch on November 1, 2020 at 4:46 pm

    First time making homemade vinegar. A food preserving group I associate with says the white growth is the mother of my homemade vinegar. Do you agree.

    • Carol Alexander on November 13, 2020 at 3:36 pm

      I would have to see. A mother usually looks like a glob of mucus swimming in the jar. Kahm yeast is a white film that floats on the top.

  6. Cory on November 4, 2020 at 9:57 pm

    I am making apple scrap vinegar. Did the first four weeks with the fruit in it, stirring every day. Now on the second week without the fruit and I now have this filmy white floating on top. I am ready to do a second straining. Once I finish straining should I add vinegar to make it more acidic, and will it get rid of the yeast, or should I just toss it all?

    • Carol Alexander on November 13, 2020 at 3:34 pm

      I am not sure, Cory. I would try doing a test. Split the batch and add vinegar to one and not the other. Hopefully, someone with more vinegar experience can help.

    • Elsi on November 30, 2020 at 5:55 pm

      Cory — could the filmy white floating be a mother? Vinegars often produce a mother which is a good thing.

  7. David on January 3, 2021 at 2:42 pm


    I just found kahm yeast on the top of my apple cider vinegar. Does it mean everything is bad and the mother will not grow.

  8. Apple Scrap Vinegar – The Urban Nanna on February 10, 2021 at 4:43 am

    […] mould or white kahm yeast develops on top of your vinegar, don’t worry too much: just scoop it off and leave the liquid […]