Wash and cut napa into halves or quarters and air dry for couple hours to rid of all water.
Weight the vegetables and calculate 2% of the total weight for salt,
(1 tbsp of salt = 1/2 oz; approx. 5 lb vegetable to 3 tbsp salt)
There are 7.5 lb of cabbage here, I use 4 - 4.5 tbsp of Kosher salt,
it's alright to use a little more or less salt, don't stress over the math.

Gently
rub salt into the vegetables until the leaves are wilted, pack them
tightly into a clean jar, put a weight on top to keep the vegetable
submerge in its liquid and seal the jar, if there's not
enough liquid to cover the vegetables, dissolve 1 tbsp of salt in 1 cup
of water and pour into the container until the vegetables are covered.
I'm using a glass pickle jar here to show you the water seal, there's a channel for water around the mouth of the jar and a bowl is inverted to keep air out. You can use any large size glass bottle for the pickle, but you have to keep an eye out for mold and be diligent about releasing gas forming inside the bottle as the vegetables ferment.
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Here are some old photos from my last post 4 years ago.
The napas have been cleaned and air dried ready to go into the 2 gallon crock,
2 pieces of stones are used to weight down the vegetables.
Put a layer of cabbage at the bottom of the crock, sprinkle some salt on top and press down, repeat
until all the cabbages are salted and pressed into the crock, it may take a while to do this.
After
couple hours of salting the vegetable shrunk and exuded more liquid, its
volume reduced by approximately 1/3 and I was able to fit both pieces of stones
into the crock, the liquid covering the stones were from the vegetables,
I didn't have to add any salt water to cover the them.
Approximately 10 days to 2 weeks of fermentation the kraut is ready to eat. Napa kraut is much milder than
regular sauerkraut, and you can use it the same way. I use it for
soups, stews, hot pots, dumplings, stir frys, etc etc.....
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For Lacto-Fermented Mustard Greens
(Sorry Thomas, this post is VERY late)
Use
3 - 3 1/2 tbsp of Kosher salt to 5 lb of thick stem mustard, air dry
the greens until slightly wilted, gently rub salt into the mustard,
press and put a weight on top to release moisture from the vegetable,
then pack tightly into a clean container, there should be enough liquid
to cover the vegetable, otherwise add salt water (1 tbsp salt + 1 cup
water) to cover it.
This post is linked to
The Gardener of Eden host of Thursday's Kitchen Cupboard, drop by Robin's place to see more preserving ideas and cooking recipes.