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.
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. Understanding what causes fermentation can highlight the importance of keeping the vegetables completely submerged during the process. And so those batches I used to find in the back of the refrigerator that were discolored were invariably never weighted down.