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I had a batch of sauerkraut fermenting in the basement. During the fermentation I had to leave for over a week and left my roommates with the basic instructions to check it a couple times and skim off any mold that might form. They forgot about it, and when I returned I found the brine level was down to the weights (but not exposing the cabbage) and that there was a full cover of dark greenish/grayish mold on the brine surface.

I've removed the mold carefully and found the submerged cabbage smelled and appeared ok, with the exception of some being slightly darker where the weights were not directly on top of it. This kraut was removed and thrown out, and only totaled about 1 cup. The mold did not contact the kraut, and the kraut itself seems to have remain submerged.

Overall I'm leaning towards it being ok, and might try small samples in cooked dishes--is this reasonable, or should I just toss it and start a fresh batch to play it safe?

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As a general rule, fluid and moist foods that have gone moldy should be discarded. It's probably not very good to give advice as whether your saurkraut is safe or not, especially since we haven't seen it. Eating a little mold is not dangerous for a healthy person though, so one could taste it and/or let it ferment further and see how it develops. I'm recommending against this though, and for starting over. –  citizen Dec 22 '12 at 20:48
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As always, if in doubt throw it out! It's cabbage and vinegar, it can't have cost much. Is it worth getting food poisoning over? –  ElendilTheTall Dec 22 '12 at 21:20
    
I doubt Genghis Kahn ( kitchenproject.com/history/sauerkraut.htm ) allowed mold to deter him from eating home made sauerkraut, nor did it deter my grandmother or my mother; but times may have changed. –  Wayfaring Stranger Dec 22 '12 at 21:41

5 Answers 5

up vote 8 down vote accepted

Per NC State's Extension's article on pickles and sauerkraut (some emphasis added):

Pickles or sauerkraut mold during fermentation.

Answer:

Unsafe—microorganisms are growing improperly.

Possible reasons

  • Fermentation temperature was above 75°F.
  • Too much salt was used, not allowing adequate lactic acid production.
  • The cloth on top of the kraut was not kept clean during fermentation (may need to be replaced after skimming).

Per Penn State Extension's Saurkraut Guide (emphasis added):

Do not taste it if you see mold on the surface, feel a slimy texture, or smell a bad odor.

Their PDF on Saurkraut says:

To avoid surface mold growth, keep the cabbage submerged at all times by covering it with a plate just small enough to ft inside the fermentation container or with two or three clean quart jars filled with water. An acceptable alternative is to fill a large, sealed, food-grade plastic bag containing 4½ tablespoons of salt and 3 quarts of water.

Again, no indication of acceptable types of mold.

I cannot endorse the existing answers which indicate that mold is an acceptable part of the saurkraut making process, unless credible science based evidence is presented, from reputable sources such as University Extension Centers or, better yet, peer reviewed journal sources.

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Interesting, and great to see cited information, but I do consider it normal to get small mold colonies which I skim off as soon as they appear. Typically they are quite small (1/8 to 1/4 inch) and look a bit like popcorn. Once skimmed they don't reappear for several days. Perhaps this is due to the location that I store my kraut, but I've never made a batch without these appearing. –  STW Apr 10 '13 at 12:45
    
From uaf.edu/files/ces/publications-db/catalog/hec/FNH-00170.pdf "Some spoilage may occur only on the surface. You may be able to remove this spoiled kraut and use the rest. However, molds that grow on the surface of kraut can change the acidity of the kraut, making the kraut susceptible to spoilage by microorganisms that are harmful. Molds grow best when they can get some air. Try to keep the kraut container airtight. Check kraut for mold often and quickly remove any mold that you see." –  Jefromi Apr 10 '13 at 13:58

Imchecked my kraut a few weeks ago, but it was not ready to can. At that time I removed a layer of gray greenish mold from the top, boiled and added more brine, put back downstairs for a few more weeks. I am canning this morning. It's ready. Once again, the mold had formed on the surface, i scraped it off, but the kraut itself was packed down tightly under 5 inches of brine. I did remove some of the kraut floating on the top after I removed the mold. It is in a pot to bring to a boil. I canned last year too, and had the mold issue. It didn't kill me to eat that kraut. I think the mold is just part of the fermentation process. I noticed this year, it is a little more sauer rhan last year, but i made a bigger batch and waited longer to can as when I checked it a few wekks ago, about half way down the crock, the cabbage was not ready. I think the mold is fine. Leave any food sitting around for weeks and yes, you are going to have mold. I don't have time to skim it everyday. I think it's just the build up of scum on the top layer and then yes it grows mold on it.

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Good that you survived. Please take a look at the accepted answer before you consider doing this again. –  Chris Steinbach Oct 21 at 18:18

My family has been brewing kraut for centuries and mold is normal. Its called "scum" when you see the scum you scrape it off the top and if your water is too low add more salt water. Dont let the mold scare you. it could be true that pink, or black is bad. ive only seen blue mold.

As far as sources go see "Wild Fermentation" by Sandor Katz

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Mold on kraut is normal and a part of the process. White, blue, green are normal. Just scoop it off and add salty distilled water to compensate for the water loss in the mold removal. If the mold is black or pink, dump it. Those colors are deadly. kraut cannot be made without mold. If you ferment the cabbage for a couple of weeks and do not see mold you have probably killed the bacteria & enzymes in the mix by using iodized salt in the primary mix. Then you need to start over and use just plan sea salt. Remember blue, green or white your alright, pink or black you are dead Jack!

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Please present credible University Extension or more scientific sources to back up this assertion that there are safe types of mold in sauerkraut fermentation. My research (see my answer) indicates otherwise. This is the 2nd question where you have presented dubious to dangerous safety information. –  SAJ14SAJ Apr 10 '13 at 7:32
    
While it's plausible that mold is safe at least in some cases if removed promptly, I have no idea where you've gotten this thing about mold colors from. –  Jefromi Apr 10 '13 at 17:56

As long as the kraut was submerged below the brine all the time it's been fermenting it would be fine. The mould forming on top of the brine is a natural by-product of the fermentation process.

It's when the kraut has contact with the air and forms mould you should discard.

I experiment with making chilli hot sauce using a similar fermentation process and the same principle applies to the chilli mash.

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How is floating in the brine, eating sugar and producing toxins different from sitting on the cabbage, eating sugar and producing toxins? –  Mischa Arefiev Dec 23 '12 at 18:08

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