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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?

  • The 2% salt is supposed to be based on cabbage weight. – paparazzo Oct 5 '18 at 16:13
  • whoa I thought it was 98% water, 2% salt; that's what the recipe I followed said; can you point me to a better recipe? because the difference would be like 2 cups of salt – jcollum Oct 6 '18 at 0:33
  • Think about it. Based cabbage just makes sense. I have not seen a recipe that in not based on cabbage. – paparazzo Oct 6 '18 at 0:57
  • I have seen several recipes that use a set amount of salt without weighing the cabbage at all. Why wouldn't 2% salt to water make just as much sense? – jcollum Oct 6 '18 at 1:31
  • Because the amount of salt lends flavour to the sauerkraut and basing it on the amount of water means how salty the result is will depend on how much cabbage you add. – James McLeod Oct 6 '18 at 2:17
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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.

If you don't want to see mold, you've surely picked the wrong hobby.

The Futility of Preventing Mold

I get that you're asking how to prevent mold, but the real question is: can you 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: mold happens. It 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 minimize it.

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.

  • 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 Oct 17 '18 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 Oct 17 '18 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 Oct 18 '18 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 Oct 21 '18 at 21:29
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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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