Making Fermented Mustard Greens

It’s spring and I happen to have an incredible abundance of mustard greens. Coincidentally, I was watching Kenji Lopez make Sichuan Beef Noodle Soup and at the end he added fermented mustard greens which is apparently a popular condiment in Sichuan noodle shops. Kenji mentions this at 20:18 in the video.

Fermented mustard greens are generally called suān cài 酸菜 (“swen tsai”) in Mandarin.

Since I have so much mustard, I thought I would try making it.

In Kenji’s video it looks like he was using the brand Yibin Yacai (Sui Mi Ya Cai, Sichuan Preserved Mustard Green) which has these ingredients: mustard greens, salt, raw sugar, compound spices (chili, ginger, Sichuan pepper, Chinese cinnamon, fennel, clove, Chinese nutmeg, garlic), potassium sorbate, acesulfame-k.

For my first experiment, I didn’t do any research on suān cài, and I decided to do a very simple 2% salt fermentation. I washed the fresh mustard greens and weighed them, and then added 2% salt by weight and a little bit of live sauerkraut from a previous fermentation. Using my hands, I mashed the mustard greens until they were fully wilted and the mustard had released its juices. Then I added it to a glass jar, placed a cabbage leaf on top, and used a weight to keep the solids below the liquid.

I did not record how long I fermented for - probably about a week - but one of the most interesting things about the ferment was the smell. After a few days, the ferment smelled like the inside of a cigarette smokers home. It wouldn’t say it was a bad smell, but it was different and interesting to me. Very clearly smokey, earthy, and grassy.

I’m not a chemist, so I asked and LLM (take all this with skepticism), and long story short, there’s a lot of volatile chemical similarity between fermented mustard and tobacco.

The final PH was 3.5 so it was in the safe zone, I ate it, and it was good. I ate it plain, but also mixed in some sugar and spices. It’s probably not to everyone’s taste, but it was a fun experiment.

I should also mention, I did another experiment where I blanched the mustard greens and did a similar 2% salt fermentation. This ferment was a complete failure. Really bad smell, some weird yeast, and very high on the PH scale. From what I read, blanching is a traditional step in making suān cài, so I’m not entirely sure why it failed. I suspect it was due to high temperatures, as I made the batch during a heat wave.