2lbs Organic lemons or meyer lemons don't use regular lemons
27 Grams Kosher salt or sea salt
Sealing and fermenting
Cut the lemons into quarters the long way, then add salt, mix, and quickly seal in the vacuum bag. Allow the lemons to ferment in the bag for 2 weeks, or until sour to your liking.
As the fermentation progresses, the bag will inflate from carbon dioxide. While I've never had a bag burst, I do cut the corner off of the bag as needed to release carbon dioxide, resealing the cut corner without using the vacuum to keep the lemons contained.
After the lemons are fermented, remove them from the bag, put them rind-side down on a cutting board, and, using a sharp paring knife, cut away the pith and seeds and discard. If you used the vacuum method, you can squeeze the capillaries and pith to extract fermented lemon juice.
From here, the lemons are shelf stable and can be held in the refrigerator, or water-bath canned in their brine if you used brine. Canning in brine will also tenderize the rind, which is a nice bonus. Do not can lemons in their juice, which could become bitter-save that for another fresh purpose like salad dressing.
Tenderizing the rind
Finally, you need to heat the rind long enough for it to become tender. My favorite way to do this is to seal in a vacuum bag and cook sous vide at 150 F for 2 hours, but you can also steam them.
To Ferment Lemons in Brine
Make a 3% brine solution by mixing 30 grams of salt for every 1000 grams of water.
Cut your lemons into quarters and pack into a large jar, such as a half gallon mason jar, or a couple quart jars.
Cover the lemons with the brine, weighing them down with an object in the jar like a clean stone to keep the lemons submerged under the brine. Allow the lemons to sit at room temperature and ferment for 7-14 days, or until sour to your liking. Seal the jar tightly then refrigerate. There is no need to turn the jars upside down.