Now hot peppers of many kinds dominate American cuisine and I've grown a fair number myself; ancho, Anaheim, jalapeno. But in recent years I've discovered serrano peppers. They can be used sparingly in cooking or salsas (I usually choose jalapenos instead for those purposes) but they make excellent hot pepper vinegar.
In the past I've picked them all green but this year they got away from me and began to ripen. I suspect this will make the vinegar even spicier. We're still using last year's batch - this is one of those things that gets better with sitting.
I found that the excellent Joy of Pickling by Linda Ziedrich had a recipe for something she calls Picque. Picque, or pique, is a Caribbean vinegar-based sauce that apparently is often made with pineapple rind and various herbs. This recipe is simpler and is great with kale, cooked Southern-style. It is also good as a brightener in cooking or salads where you might add a squeeze of lemon juice or other splash of acidity.
Picque
adapted from Joy of Pickling
Clean serrano chiles (green or mixed green and ripened) and remove most of the stems. Slit with a knife but leave whole. Choose glass bottles with non-reactive caps (old vinegar bottles with dispenser tops are ideal).
Divide these ingredients among the bottles. (You'll have to guess how much in each bottle depending on the size of the bottle.)
4 garlic cloves, halved
12 whole black peppercorns
1/8 t pickling salt
12 whole black peppercorns
1/8 t pickling salt
Push serrano chiles into the bottles as tightly as possible. Pour unheated, undiluted cider vinegar directly over the chiles to fill the entire bottle.
Note: The recipe is for 1 cup of cider vinegar; divide the other ingredients according to the size of the bottle. The chiles take up a lot of volume and I typically get two bottles per recipe.
Shake the bottles to dissolve salt, cap, and let sit in a cool place for several weeks before using. You may refill the vinegar once, but it won't be as good.