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Related My sauerkraut has mold covering the surface, is it ok? -- but this asks if it's ok, I am thinking it's not OK and want to prevent it from growing at all.

Usual setup:

  • 3 heads of cabbage, shredded and mashed
  • 5 gallon bucket, food safe, with lid, kept in basement
  • dinner plate on top of kraut, quart of water on top of plate
  • 2% salt-water solution to cover kraut, with 2 inches of extra water
  • all floating cabbage scooped up

I still get a lot of mold on the surface and it just grosses me out. Talking about 5-10 quarter-sized patches of mold. I've seen suggestions like putting a cabbage leaf on the surface, which still results in mold, it's just on the cabbage leaf.

Do I need to scoop all the kraut into jars at the 3-4 week mark? I was under the impression that you just leave the kraut in the bucket and transfer a jar's worth out when you need more in the fridge.

Is there a tried and true method for stopping any mold from growing?

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4 Answers 4

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Brining vs. Dry-Salting

Vegetable fermentation is normally done by one of two methods:

  1. brining (submerging whole or chopped vegetables in brine)
  2. dry salting (mixing chopped vegetables with salt and letting osmotic magic draw fluid from the vegetables to create a brine)

I'm pretty sure you're describing a brining process. Kraut is normally a dry salted application. Sandor Katz's "The Art of Fermentation" is a bible for this sort of thing. See Chapter 5 for a discussion of this; he lists kraut and kimchi as the classic examples of dry salting. You might want to try a more traditional dry-salting process. Katz's Wild Fermentation site has a weight-based dry-salting recipe.

Having said that—it won't guarantee you get no mold.

The Futility of Preventing Mold

I get that you're asking how to prevent mold, but the real question is: Can you absolutely, 100% of the time, prevent mold?

Maybe you could with with an industrial-grade setup, but I'm not even sure of that. I've been making kraut and many other vegetable ferments for almost a decade now, and I can tell you this: Sometimes mold happens. It doesn't have to happen often (I see it very rarely), but if it does? That doesn't mean you did something wrong.

From The Art of Fermentation section "Surface Molds and Yeasts" (p. 103 in my hard-cover printing):

"An inevitable aspect of [fermentation] technique is the edge, where (in an open vessel) the surface of the liquid... comes into contact with oxygen-rich air. The meeting... encourages rich biodiversity, where molds and yeasts frequently develop. Surface growth is common and normal; it should be removed, bit is not cause for alarm and it does not ruin your fermenting vegetables."

Minimizing Mold

Having said that—I'm with you. Mold grosses me out. I try to prevent it, and usually I can.

In my experience, the wider the vessel's neck, the more mold and kahm (yeast) develop. I have good results with 2-quart mason jars, which have a low neck-to-volume ratio. That minimizes the "edge" that Katz describes. For large batches, that means multiple 2-quart jars, but the control is worth it to me.

I also check the surface of my ferments every 2-3 days and skim off any developing kahm or mold. Every time I check, I'm exposing the surface to more mold and yeast spores... but if I catch it when it's the size of a pinhead, it won't grow to the size of a quarter.

I've also had much better success since I started using actual fermentation weights and vented lids for my mason jars. Any will probably do, but I've been using this weight and this lid.

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  • I was considering putting CO2 on top of the water surface actually (with a one-way valve in the bucket lid). Sounds like those fermentation jars at the end are doing similar things... Also it's surprising that Katz doesn't say anything about mashing the kraut. I assume he is just letting the salt do the work? I've also wondered if freezing the kraut would speed the cell-breaking process along (probably too much though, might get mushy). Great answer, thanks.
    – jcollum
    Commented Oct 17, 2018 at 23:26
  • Also I have those weights -- they could use a better design, they are hard to pick up if they are wet.
    – jcollum
    Commented Oct 17, 2018 at 23:27
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    @jcollum These weights are designed to address that slipping problem: amazon.com/gp/product/B076V66FZ4. Lehman's Hardware in Ohio also has good supplies; for anybody, but they cater to the Amish/Mennonite community there, where preservation is important: lehmans.com/category/fermenting-pickling. As for mashing, step 4 of his recipe is what you're looking for (he calls it "tamping"). I use a wooden cabbage pounder -- had to sand it to fit a wide-necked mason jar. CO2 production is only high for the first week or two; after that, you're probably more susceptible to mold.
    – Andy Giesler
    Commented Oct 18, 2018 at 13:30
  • Those weights don't look different enough to address the issue. A good glass weight would have an "omega" shaped handle in profile -- you need to be able to curl your fingers a bit under it to deal with the slippage. Learned that the hard way after I bought weights that didn't have that. Or a bit of sandblasting on the grip area would do it maybe
    – jcollum
    Commented Oct 21, 2018 at 21:29
  • I've been using the process I outlined in my answer below for 2 years now and have never seen any mold. It's 100% possible to make sauerkraut without mold.
    – jcollum
    Commented Nov 6, 2020 at 23:44
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I have been told that by taking a plastic bag and turning it inside out (to get a surface which is cleaner and presumably there shouldn't be mold spores on the inside of a new bag), fill it with water and place on the top of the ferment to keep it anaerobic. The gases can escape around the edges of the bag but oxygen entering should be minimal. Hope that this helps!!

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  • Not a bad idea. Hard to pull off in a 5 gal bucket
    – jcollum
    Commented Jan 11, 2020 at 1:57
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Been a while but the real solution for this for me was to use "Waterless Airlock Fermenter Lids". You put the kraut into off-the-shelf mason jars, pump out all the air and put the kraut on a shelf for a few weeks. Zero mold, every time. I've done it about 6 times now.

There's an answer here that says something about "The Futility of Preventing Mold". Well, I managed to prevent it by taking away the oxygen. Lactobacillus does not require oxygen, mold does.

https://smile.amazon.com/gp/product/B07921Y1CY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I add 2% salt to the cabbage as I tamp it into the jars (100g cabbage + 2g salt)

edit to add: at this point, 2 years later (!!!!!) this process still works great, I haven't seen mold in my kraut since then

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    I always push anaerobic ferments to people, especially people just starting out. You can totally get successful open-air ferments, but it can be iffy. Thorough preparation (including equipment sterilization), temperature control, and oxygen control are all incredibly important factors in fermentation. I'm glad you found a solution!
    – kitukwfyer
    Commented Oct 31, 2020 at 1:04
  • Totally. Anaerobic removes the variable of mold in your air -- which apparently I have plenty of. I'd need to put in an air filter near my ferment if I was trying for a ferment without the air-lock lids.
    – jcollum
    Commented Nov 2, 2020 at 16:47
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If you don't want mold and are willing to get something similar to sauerkraut, use Asian-style fermentation. The Laotians use cooked rice (usually sticky but I don't think it matters) soaked in water. And the Koreans use rice flour which gets cooked in water. Either way, the addition of the rice accelerates the fermentation and instead of taking months it takes a few days depending on the ambient temperature. This would not leave much time for mold to grow.

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