What is Kahm Yeast & Is it 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 kahm yeast 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 kahm yeast looks a little funky, it is not something that is harmful to you or your ferment.

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 here had an airlock during fermentation – not to worry, everything tasted fine!

Some people prefer to remove the kahm 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?

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.

  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.

Leave a Comment