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Have you ever kept a batch of kraut around long enough to see it discolor at the top? This happened to me recently. It’s been so long since this happened – because we usually eat our ferments so fast – that I had kind of forgotten about the phenomenon.

But I remembered back when I used to keep ferments in a refrigerator in half-gallon jars. Eventually I had some of the top of the kraut go from green to brownish. Or, in this case, a jar of kimchi ended in two completely distinct coloring patterns – the red of the chilies at the bottom and the blah brown cabbage at the top.

It turns out there is a chemical compound that causes this to occur and, thinking back on the occurrences, I think I may have figured out why it happens. Or at least I have a guess.

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The good old Journal of Food Science came up when I did a bit of research. I’m kind of a science geek myself and even committed my four years of college to chemistry. But food science is what really interests me, which is probably why fermentation is such a fun-filled and geeky process in our house.

Anyway, this article abstract in the Journal of Food Science claims that the compound causing the color change is leucoanthocyanidin. It’s a mouth full, to be sure. The funny thing is I opened the jar of kimchi, thought it smelled delicious, and gave it a taste before even reading up on this. The flavor was great with tons of tang and spice. The texture was a bit limp compared to a similar jar with no discoloration, but certainly edible.

So, what is it that might be causing this compound to form? Well, I don’t know for sure, but I have a guess. For my first few years of vegetable fermentation I never really bothered with weights. The brine sort of went to the top of the vegetables and I hadn’t come across what I now strongly believe to be one of the most important aspects of vegetable fermentation – keeping the vegetables completely submerged. And so those batches I used to find in the back of the refrigerator that were discolored were invariably never weighted down.

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Fast forward to now and I always use weights in my ferments. Generally it is these ceramic fermentation weights, but I’ll also throw a cabbage leaf or root vegetable slice in there if need be. Just anything to keep the veggies down.

This batch had those weights until we started chowing down on it and then someone removed them. And it sort of just sat out at room temperature for several weeks before I opened it up again and found the discoloration.

So, maybe no brine covering the top of the vegetables = leucoanthocyanidin = discoloration? That’s just my guess. I also think that adding more brine if your vegetables aren’t well covered by a couple of inches of brine or are not in an especially cool location helps.