Slice your jalapenos. When slicing your jalapeños, you might want to wear some gloves to avoid getting the oil on your skin and elsewhere later. I don't like to do that and sometimes I pay for it, lol. So be warned!
Fill your jar. Add the jalapeños to your mason jar. It should be near full. To about an inch and a half below the rim.
Make your brine. Add 2 tablespoons of salt to one quart of water in a separate jar. Stir or shake well to dissolve the salt.
Add the brine to your jalapenos. Pour the brine over your jalapeños. They need to be submerged. If you have leftover brine, you can save it for another ferment or use it in your next soup or bread instead of salt.
Weigh down your jalapeños. Place a glass fermentation weight on your jalapeños. If you don't have one, you can use a boiled, clean rock, a baggie filled with marbles or brine, or some other food-save, non-corrosive item you have on hand.
Cover your jar. If you are using a mason jar, I highly recommend a fermentation lid. They are self venting and are so easy to use. No maintenance necessary. If you don't have one, you can use a 2-piece mason jar lid. But you'll need to remember to burp it once a day. Or you can try to screw the band on very loose, so it can self vent. But keep an eye on the fermentation to see if a yeast layer forms on top, which is harmless, but should be skimmed off or it will make your fermentation taste off.
Place your jar in a dark place with a bowl under it, at about 70-80 ℉. This temperature should be maintained over the course of the next 3 weeks. Some fluctuation is fine, but avoid prolonged lower or higher temperatures. For more details on fermenting and why it is important, visit my lacto-fermented vegetables page that is a beginner course on fermenting.
After 3 weeks of fermenting your jalapeños, they will have turned an olive color. Open the jar and smell them. They should have a pleasant tangy scent and be firm and crunchy. Now Taste them. If they are nicely tangy and you like them that way, you can refrigerate them at this point. Fermenting them for three to four weeks for a full fermentation yields the highest health benefits.
If for some reason your ferment smells putrid or seems slimy or mushy, you probably don't want to taste it. Something went awry. But it will still make great food for your compost. It's very unlikely that anything will go wrong, if you followed the instructions and used clean equipment, but when you're dealing with live foods, stuff can happen. Maybe your temperature was too low or too high or your jalapenos had been treated with pesticides. It's always a bummer, but remember, while it can happen, it is not the norm. Don't be discouraged and do try again. If they taste good to you, then close the jar with a regular lid and place it into the refrigerator. Here it should last at least a year or more. Use as needed. Be sure to save the juice and drink a bit of it each day as a tonic, or use in salad dressings, sauces or soups for a great flavor.