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We started a batch of sauerkraut about a month ago. We used the outer leaves of the cabbage to cover the shredded cabbage below. The cabbage was brined with adequate salt (about 2 tsp per pound). The brine level was well above the surface of the cabbage, which was displaced even more by a plastic bag filled with additional brine.

We last checked it about a week and a half ago, but the brine was at the same approximate level.

Today we checked it, and the brine level was below the surface of the cabbage. The top leaves smelled musty, so I removed them, as well as the 2 or so inches of cabbage below them. At that point, the cabbage smelled exactly as it should - salty, lactic-acidy. It also tastes excellent.

Most recipes I find simply note that if the brine level drops below the surface, just add more brine. My concern is that I don't know how long the brine has been below the surface.

I know most toxins can't survive in a lactic-acid/salt-rich environment, so are we ok? I am planning to hot pack and can today just to be safe, but it seems to be passing all visual/taste/smell tests. My biggest concern would be botulism, but botulism can't survive with that amount of salt.

Am I ok? Or should I err on the side of caution?

  • Personally, I would do as you did...remove the surface layer, proceed as usual. As long as there is no mold or slime, and botulism is not a concern in the brine, of course. – moscafj Oct 1 '16 at 20:19
  • Salt -- sodium chloride -- does not prevent botulinum growth. However, oxygen does. Salt also has no effect on the botulinum toxin if it's already been produced. – jscs Oct 2 '16 at 0:54
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    It is the lactic acid environment that is important for safety in kraut. – moscafj Oct 2 '16 at 13:19
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    You got my comment backwards, @AndyGiesler; I'm sorry if it was worded badly. Yes, presence of oxygen prevents growth; lack of oxygen enables. – jscs Oct 2 '16 at 17:43
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    Yes, although it's worth noting that the spores do not mind the presence of oxygen; but they're also inert. It's when they germinate that the toxin is produced, and that only happens in an anaerobic state. This is the thing that makes botulinum so insidious, to my mind: you're right that lack of oxygen prevents all kinds of other nasties like mold, but C. botulinum exploits that niche. – jscs Oct 2 '16 at 18:06
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Unfortunately nobody can give you a definitive answer about your batch without testing. But I can give you more information to help you make a more informed decision.

As you are, I'm concerned about botulism. You mention that "botulism can't survive with that amount of salt". I'm not sure whether that's true. If an environment is salty enough, or if it's less salty but acidic enough, you're all set. But the question is what's enough; at some point it's far less likely, but not impossible, for clostridium botulinum to survive.

Your primary defenses were (1) a salty, acidic environment below the surface, and (2) oxygen at the surface. It's hard to know whether the cabbage tissue at the surface was anaerobic enough; maybe so. As for acidity at and near the surface, if mold was involved somehow that could lead to a drop in acidity. From Sandor Katz's excellent The Art of Fermentation, p. 50:

Molds can also digest lactic acid, lowering the acidity of the ferment that enables it to be effectively preserved.

So...

  • if the surface environment became tolerable for c. botulinum, and
  • if it grew in that environment, and
  • if it produced botulinum toxin, which then got into the submerged kraut

then as I understand it, boiling and canning won't change the presence of that toxin unless you boil it for at least 10 minutes. (Thanks to Josh Caswell for pointing this out in the comments).

On the other hand... that is a whole lot of ifs.

I'm just an informed layperson, so you'll need to make your own food safety call based on this and information from others. My guess: your kraut is just fine.

But because I always err on the side of caution, in the same situation I'd probably chuck the batch (with tears in my eyes). Though not in this exact situation, I've done it many times, and it hurts, but I sleep better, especially since I share my ferments with others.

Or if your "hot pack" will heat the kraut long enough to address both botulinum spores and toxin—I know nothing about canning—you're probably fine too. I'm not sure what that does to the kraut's texture, and you lose probiotic benefits, but it sounds like addresses the safety concern, at least for botulism.

Some more sources:

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