Fermentation, Food
Comments 6

what about the white film on my Sauerkraut?

Last night I was serving a friend dinner. Roast lamb and veggies with homemade sour cream and sauerkraut. My 3 gallon batch of fermented cabbage, burdock, apple, cranberry, seaweed and herbs was ready to harvest after bubbling for several weeks. I lifted the lid off the crock and found the surface of the brine covered with a thin white layer of yeast. This is the same yeast that I find on top of my sourdough starter, so I just wiped it away and pulled out a cup of kraut for us to eat.

white film on Sauerkraut

My friend curiously looked into the crock and asked about the white film. I told her it was yeast and that it’s not a problem. There is lots of yeast living in the air of my house since I have been fermenting for so long. ( this picture shows little bits of the yeast after I scooped most of it off)

But this morning I woke up with some nagging doubts. Is the yeast really not a problem? It is what I remember hearing from my fermentation teacher, Sandor Katz, years ago. And I have been eating it and not getting sick. But when I am serving other people I like to be sure that I am being safe.

A little online search brought me to this fabulous post on the science behind fermentation by Nourishing Treasure. This is what she has to say about yeast and the white film on top of the kraut

A Word on Yeasts

Yeast is another major inhibitor which requires an abundance of oxygen for growth. It’s often one of the first signs that you’re allowing too much oxygen near your sauerkraut. In the presence of oxygen yeasts can be oxidized to form vinegar – not something we want in our sauerkraut. Yeasts can also cause off-flavors and discoloration, visible signs you need a better seal on your sauerkraut. Pink sauerkraut (not from red cabbage) is a sign of yeast. This could be due to too much salt, or an uneven distribution of salt, or too much oxygen exposure. If you see a creamy film on top and/or one that smells yeasty, throw it out.

There is one yeast, however, that is helpful. Saccharomyces cerevisiae, a member of the ascomycetous yeast family (as opposed to the candida family) is probiotic and can help with candida overgrowth. Interestingly, Saccharomyces cerevisiae has the ability to shift its own metabolism from fermentive to oxidative. Do you know what causes it to make the switch? Oxygen. When present, oxygen will cause Saccharomyces cerevisiae to oxidize; keep the oxygen out, and this friendly yeast can help your sauerkraut to ferment and provide you with delicious probiotics.

White Film, Slime

Although mold is harmful, white film is not. This is just your friendly probiotic yeast at work. This happens more often when cabbage isn’t properly submerged under the brine, or the container isn’t sealed well.

Slime, however isn’t to be tolerated. This is most often the cause of too little salt, or salt that wasn’t evenly mixed into the cabbage.

There is my answer. The white, non slimy, film on top of my kraut is indeed yeast which has probably started to grow more because I stirred it up last week and let some fresh oxygenated air in. I had been scooping cups of kraut out while I was waiting for the fermentation to complete. In the future I will avoid stirring it up so much, to keep the oxygen out. This batch is ready to go in jars and be eaten.

white film on Sauerkraut

In case you are wondering what the yeast looks like before it is disturbed, one of the tell tale signs is that the film crinkles up when you push it to the side and it smells fresh. I didn’t think to take a picture of it before I scooped it off, but Herbangardener has a nice picture of the white film on top of her Beet Kvass. It is towards the end of the post under troubleshooting.

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6 Comments

  1. Thanks for this, Catherine. As a novice fermenter who has been slacking on research it is very helpful to know. I basically started fermenting first and am learning the ropes as I go. The part about the slime is very useful, I’ve had that happen to my batch and though a little put off still ate it all up. I lived to tell the tale, but will not repeat it. The hardest thing about fermenting for me is spending the time, love and money to make a beautiful batch of yummy kraut only to have it flop after days of anticipation. Often I sense that things aren’t right, but I refuse to believe it, and eat it anyway, you have convinced me to be more connected with my kraut, it is a living organism after all.

    It funny that we have to rot our food to perfection. And I tend to fall in love with it in a way too.

    Do you have any suggestions for the best equipment to use, to limit oxygen and increase the likely hood of a successful batch?
    I use a crock, but it did not come with a lid, but I found a plastic lid that fits into it and I usually weight it with a squash or rock, but there is a tiny bit of room around the edges, and as the fermenting gets going it bubbles up and so I am opening it to smash it back down, which I will avoid now.

    Thanks again!

    • Hi Ami,

      I use a big crock with a plate and a rock and push the stuff back down around the edges. I think that method works great and I never get mold, and only occasionally a little yeast at the very end of the cycle, which is harmless.
      In fact I was told by my fermentation teacher to check on the kraut, mess around with the surface and taste it from time to time. That way any bits that stick out get submerged and no molds can grow. This last time I had stirred the entire batch, exposing it to lots of air, that’s what I won’t do again.

      If you’re curious about some containers that don’t let any air in, I suggest you check out this post. http://www.nourishingtreasures.com/index.php/2012/07/03/sauerkraut-survivor-final-report/
      She did an experiment with 18 different jars and crocks.

  2. That was a very informative post. Sandor Katz mentioned that the yeast/mold should be cleaned before it gets colors, which is usually a sign that it is going through cycles and replicating.
    John S
    PDX OR

  3. Daniel says

    Thank you so much for this – my sauerkraut has been floating to the top, and, as a result, growing this white (but non-slimy) film and undergoing an unpleasant change in both smell and flavor.

    • Daniel, you want your veggies to always be under the top of the water. When they are exposed to air unwelcome yeast, mold, bacteria can grow. Make sure you have a plate with a weight pushing the cabbage down. And/or top off with a little salty brine.

      • John S. says

        You can get a white film on top of the water, even if the vegies are under a plate and rock. The white film is fine. It’s a probiotic kalm yeast (not a frantic yeast :)).  Clean it off anyway, as well as you can, because if you just leave it, hairy blue mold will grow on that, and the hairy mold is not good for you. 

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