Top layer of cabbage darkened?

Ditto what Mutedog said.

With all lacto ferments, food must be kept below the brine level. With a short ferment (like small pickles under a week), its not a huge issue as not much has time to grow, but for a 2-6 week ferment like kraut, it's essential.

Without knowing your prep method beyond your picture, I'm going to make suggestions that may or may not apply to your current jar:

-Did you crush and then tamp your cabbage tightly into the jar? If the cabbage is fresh, there should be plenty of liquid being released to not only cover the top of the cabbage and your weight, but for me, typically an excess that sometimes escapes my airlock.

I pack it in with a tamper. It was covered in brine over the top of the weight. The water just disappeared.

-You appear to be using a Fido type hermetic sealing jar. I don't see an airlock on the lid, and you run a serious risk by fermenting things in competently sealed jars. Fido jars are like little tanks and would take a lot to shatter, but when you open one after gasses build up, you will likely wear your kraut. I use these for my kraut and other ferments: https://www.itsygarden.com/posts/making-a-fermentation-jar-for-pickles-sauerkraut-and-other-probiotic-foods/

It has a hole in the lid with a silicon airlock.

-Did you use a weight? (In your picture there does not appear to be one). When fermenting small bits, a weight is going to help keep your cabbage from reaching the surface of your brine. Using an outer leaf from your cabbage placed below the weight is also a good practice as it acts like a little kraut umbrella. ;) (the link in the point above also gives suggestions for weights, both for purchase and quick DIY)

A glass weight, just took it out.

Lastly, did you use enough salt? As a rule you will want about 2 tsp of non-iodized salt per 1 lb of shredded cabbage. Why non-iodized (aka table salt)? Because it can cause discoloration. Sea salt, canning salt or kosher salt are best, but if you used table salt, no worries, it won't affect the taste. Ideally you will cut your cabbage, crush it with a rolling pin or even your hands, add salt and crush a little more. Brine will appear very readily after this, especially as you press it tightly into a jar. Keep adding salted, crushed cabbage in layers into you reach the neck of the jar and then apply an airlock lid. Set the whole jar in a baking pan in case of overflow, especially if its a warm room.

2.5% Sea salt of weight of ferment.

After 2-6 weeks depending on taste preference, you'll have sauerkraut. =)

It goes fast here, ambient temps 80-90f.

As for your current jar, I would remove any discolored bits and make a quick 5% brine (recipe for brine is 2tbsp+2tsp salt for every quart of water) to cover the rest. It might not be as good as your next batch but it will still be tasty.

I just tossed the entire top half.

I do have a sauerkraut article/video tutorial in production right now, but it won't be ready for another 2 weeks (deli pickles will be up this weekend though using that same fermentation jar).
If you have any questions about the tips above, don't hesitate to ask me here or at my website: www.itsygarden.com

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