This is a simplest recipe to ferment this bitter and spicy mustard green with the large thick crunchy stems. After a few days 3-5 five days in the warmer weather and maybe a week in colder weather, they will become sour and crunchy without any vinegar. There are several ways to do it. Some boil the brine and dip the green into the warm brine to wild them. Some place the green under the sun to wild them. Some add vinegar. One day I learned this way from a friend-she skipped every extra steps and the fermentation is still happened and good too. How easy than this: the mustard green only needs to be cleaned, cut and add to salt, sugar solution. Done.
A large, clean, non metal (preferred glass or ceramic) jar or several old pickled jars or a large container which can hold the green.
Fresh Asian Mustard Green/cai lam dua (the one with large, thick stems) it is sold in packages at Asian stores
1 or 2 shallot or 1 small yellow onion, thinly sliced
Sea salt or table salt: 1 Tbs and 2 tsp (30 gram) for 1 litter/quart water
Sugar: 1 tsp for 1 litter of water
Water enough to cover the green in containers
Cut mustard green including the large center stems, into 1-2 in sections, wash and rinse well. Place the green into the container, top with onion slices, and cover with water. Measure the water when pour it over the green. Calculate the salt and sugar as above ratio. Then place sugar and salt in a medium bowl, pour some water from the container and mix well until all salt and sugar dissolved. Pour back to the container and shake or stir the water make sure all sugar and salt are even distribute in water. Press the green down and place a small plate or a plastic bag filled with a little water. Make sure all the green is cover by the brine, try to press the green down occasionally/ daily is ok. Cover with the lid. Leave the jar at warm place in the room.
If the weather permits, put the jars near the warm window or outside in the warm weather during daytime. It will help speeding the fermentation up. The color will change from green to yellowish green. The brine maybe turn lightly cloudy and slimy at the first few days and bubbles will appear during the fermented process. When there is little of green color left on the stem. Taste to see if it is ready to eat, it should be sour and lightly salty. If it is sour enough to your taste. Store the container in the fridge to slow down the fermentation. It lasts a long time in the fridge.
We usually eat this as a side veggie dish with stewed, boiled pork or fish.