Vegetable · leafy

Lacto-fermenting mustard greens (gai choy): 2.50% salt, 10.0days at 68 °F

Mustard greens — sold as gai choy in Chinese markets and called dai gai choy when mature — are the foundation of Chinese suan cai, a sour fermented green that predates Korean kimchi by centuries. The sulfur compounds (glucosinolates) produce a sharp, almost horseradish-adjacent tang during fermentation. Less common in Western fermenting circles but extensively documented in Asian fermentation literature.

Salt calculator

Enter your vegetable weight and a salt percentage. We return the exact salt mass in grams, plus teaspoons for each common grain.

grams
%

Grain matters: one teaspoon of Diamond Crystal weighs half as much as one teaspoon of fine sea salt. Weigh in grams when you can.

25g salt
4.39 tsp 1.46 tbsp 0.88 oz

Based on Fine sea salt at 5.69 g/tsp.

Safe range for lacto-fermentation. 2% is the most common default for cabbage, kimchi and pepper mash.

All salt grains
GrainGramsTeaspoonsTablespoons
Diamond Crystal kosher25 g8.82.93
Morton kosher25 g5.211.74
Fine sea salt25 g4.391.46
Pickling / canning25 g4.551.52
Default salt
2.50 %
Salt range
2.00% – 3.00%
Time @ 68 °F
10.0 days
Target pH
3.40
Water content
~90%
Preferred styles
kimchi baechu, lacto ferment, suan cai

Technique

Separate leaves from the central rib. Wash thoroughly (mustard greens trap grit). Drain. Pound or massage with 2.5% salt by total weight until leaves wilt and release liquid (8-10 minutes). Pack tightly into a wide-mouth jar with a 1-inch piece of ginger and one whole dried chili. Weight, ensure brine covers leaves, leave 1 inch headspace. Ferment 7-14 days at 65-72°F. Liquid will turn slightly cloudy and smell sharply sour — this is correct. Soft pink discoloration is normal from leaf pigments; gray or fuzzy growth on top is mold and the batch should be discarded.

Source: Katz — The Art of Fermentation (p. 105, Suan Cai). Last verified 2026-06-20.

Frequently asked questions

What percent salt for fermenting mustard greens (gai choy)?

2.50% by weight is the default for mustard greens (gai choy) (workable range 2.00%–3.00%). For 1000g mustard greens (gai choy), that's 25.0g salt. Use non-iodised salt and weigh in grams — teaspoon equivalences vary by salt grain. Source: Katz — The Art of Fermentation (p. 105, Suan Cai).

How long to ferment mustard greens (gai choy)?

10.0 days at 68°F (20°C). Cooler kitchens (60-65°F) slow fermentation; warmer kitchens (75-80°F) roughly halve the time per 10°F increase. Start tasting from day 5; target pH 3.40 or below indicates complete primary fermentation.

What's the best technique for fermenting mustard greens (gai choy)?

Separate leaves from the central rib. Wash thoroughly (mustard greens trap grit). Drain. Pound or massage with 2.5% salt by total weight until leaves wilt and release liquid (8-10 minutes). Pack tightly into a wide-mouth jar with a 1-inch piece of ginger and one whole dried chili. Weight, ensure brine covers leaves, leave 1 inch headspace. Ferment 7-14 days at 65-72°F. Liquid will turn slightly cloudy and smell sharply sour — this is correct. Soft pink discoloration is normal from leaf pigments; gray or fuzzy growth on top is mold and the batch should be discarded.

What category is mustard greens (gai choy) for fermentation?

Mustard Greens (Gai Choy) is a leafy vegetable. Mustard greens — sold as gai choy in Chinese markets and called dai gai choy when mature — are the foundation of Chinese suan cai, a sour fermented green that predates Korean kimchi by centuries. The … Preferred fermentation style: kimchi-baechu, lacto-ferment, suan-cai.

The kit for fermenting Mustard Greens (Gai Choy)

A short, honest kit for lacto-fermentation. The scale is the one that matters most — everything here is by weight.

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