There are a lot of traditional preserved lemon instructions/recipes, and they usually are just lemons and salt. Some recipes include an herb sprig or peppercorns. The combination of lemons and salt makes this product very low risk for any pathogens.

In all the recipes, lemons are carefully washed and then are cut into quarters from one end, but not quite through the other, so the lemon opens up but doesn’t break apart. Salt is placed in the cavity to coat all the sides of the lemon slices the lemons are closed again. The outside of the lemon is also coated with salt. I have seen recipes from 1 teaspoon to 2 tablespoons salt used for each lemon.  They are then pressed into a jar to allow juice to fill in air spaces. Some recipes call for additional freshly squeezed lemon juice to fill in all air spaces. Make sure the lemons are submerged in juice. These can be safely left at room temperature for the first few days to allow the salt to dissolve. Then we suggest storing it in the refrigerator.

The salt will keep the lemons from decaying and molding for an extended period of time, so it needs to be an adequate amount. Watch for any signs of sliminess or mold and discard the mixture if that happens. Practice good hygiene when preparing this to reduce the likelihood of contamination. 

Cover loosely. The lemon and salt will corrode a canning jar lid, so a loose plastic lid or lining a metal lid with plastic wrap and leaving that loose is suggested.

Hope this helps.