Trim the tough base off of the mustard greens, along with any yellow or brown portions of the leaves. To remove any dirt or sand, soak them in a large bowl of water for 10 minutes. Shake the vegetables to loosen the grit. Lift the vegetables out of the dirty water and rinse. Rinse the bowl, fill with fresh water, and repeat this process two more times. This cleaning step is very important.
In a large pot, add 10 cups (2.4 liters) of water, bring to a boil, and turn the heat down to medium low. Stir in 1 ½ tablespoons (26g) of salt, until dissolved.
Place the mustard greens into the simmering water 1 or 2 at a time, so they’re completely submerged. Blanch for 30 seconds, rotating them to evenly heat them on all sides. Lift the mustard greens out of the water and transfer to a clean sheet pan to cool.
Next, put the sliced ginger into the blanching water and bring the water back to a simmer. Once simmering, turn off the heat, and allow the liquid to cool to room temperature.
Once the vegetables are cool enough to handle, pour off any excess water from your sheet pan and rub salt (2 ¼ teaspoons/13g per pound of mustard greens) all over the greens, getting into the inner stems and rubbing the salt evenly across each stem/leaf until it has dissolved.
Place into a non-reactive bowl—stainless steel, enamel, ceramic, or glass work—and pour the ginger-infused blanching liquid over the vegetables. Place a large plate on top of the vegetables with a heavy pot (or a pot filled with water) on top to press them down and keep them submerged. Allow the greens to sit in the salted water for 24 hours at room temperature, covered with a clean towel or paper.
Disinfect the jar by first washing it thoroughly. Wash your hands, and rinse the jar with boiling water. With clean hands or tongs, lift the mustard greens out of the brine solution and let any excess liquid drain for a few seconds.
Squeeze the vegetables tightly. This removes spaces where air bubbles can form, and also makes them more compact. Place them into the jar along with the ginger slices. Do your best to squeeze the vegetables into the jar and distribute the ginger evenly. Reserve the brine, as you will be adding it to the jar momentarily.
Measure 1 teaspoon (6g) salt and ¾ teaspoon (3g) sugar per pound of greens, and sprinkle on top of the vegetables in the jar. Measure out 2 tablespoons (30 ml) white vinegar per pound of vegetables, and pour it over the salt and sugar in the jar.
Next, use a clean ladle to carefully transfer the brine into the jar until it is almost full. Check for air pockets that may be trapped near the bottom of the jar. Use a chopstick to move the mustard greens around to release any air bubbles. You can also cap the jar and move it around to coax air bubbles up to the top. Once you feel all air bubbles have been eliminated, fill the jar to the top to ensure that all of the greens are completely submerged in liquid.
Take a 10- to 12-inch square piece of plastic wrap and fold it in half twice to make a neat smaller square. Place it over the jar, making sure there are no air bubbles under the plastic wrap. Screw the top on over the plastic wrap to create an airtight fit.
Use a clean kitchen cloth to wipe any liquid from the jar and place a label on it with the date. Place the jar in a cool dark place for about 2 days, or until the mustard greens have turned from a bright green to a dull green.
After the mustard greens turn a dull green (2 days), put them in the back of the refrigerator, and they should be ready to eat in 7 days.
Store in the back of the refrigerator in the jarred brine. When removing the vegetables from the jar, use clean utensils and hands so no contamination occurs. They can be kept in brine for weeks in the refrigerator, but they are best eaten within 1-2 monthsNote: Salt content in nutrition information is an estimate, as we are unsure how much salt from the brine is actually absorbed into the greens.