Rinse and drain the jalapeno peppers. Then don a pair of disposable foodsafe gloves, if you have them.
Cut off the stem ends of the peppers, then slice the peppers into rings.
Add the vinegar, sugar, and salt (if using) to a large saucepan (large enough to hold all the peppers later, too). Bring to a boil.
Add the sliced peppers into the boiling brine, and bring it back to a boil. Boil the peppers for 4 minutes (only 2 minutes if you plan to process them in a water bath), stirring occasionally to make sure all the peppers change colour from bright green to a dull green.
Ladle the hot peppers and brine into clean jars. Seal with a lid and let cool. Store the jars in the refrigerator for up to 3 months.
If you choose to process the jars in a water bath, so they can be stored longer (2 to 3 years) unrefrigerated, use sterilized jars and hot lids and process pint jars for 10 minutes using proper canning procedures.
Notes
You can vary this recipe by using different types of vinegar, like apple cider vinegar or white wine vinegar. You can also add a spoonful of pickling spice to each jar, or add a clove or two of garlic to each jar, or a handful of sliced onions to the pot when boiling the peppers. You can add a spoonful of turmeric to add flavour and a yellowish colour.Jalapeno peppers can vary in heat level from batch to batch, so some batches may be 'hotter' than others.