Pickling is a traditional method of preserving food using a mild acid such as vinegar to prevent the growth of bacteria.
When you pickle onions you soak them in Brine (1 part Pickling salt, 2 parts water) before placing them in the pickling solution this helps draw out the water from the onions, this can also be done with thick fleshed chillies. Before you soak the chillies it is best to make a few holes in the chillies to allow the solution to enter the chillies, they should be soak for between 4-12 hours. The brine soaking help they remain crisp and crunchy
Make sure you have jars are clean and well sterilised in boiling water before use, I like the Kilner style jars as they are easy to clean and reuse.
After you have soaked the chillies in the brine, remove them and carefully dry them making sure there is little or no brine left inside them, then place them in a jar as tightly as possible.
I have also sliced my chilles into 1 cm rings and pickled them as well, they unfortunaty they did not last long as I had them with almost everything.
A simple pickling solutions can be made from:-
500 ml Water
500 ml Distilled/White or Cider Vinegar
2 tsp non-iodized salt
Place the ingredients in a large pan and bring to the boil, and then cool for 10 minutes and then carefully pour over your chillies and seal the jar, invert the jar so that the pickling solution can enter the holes in the chillies and then top up the jar if required.
Air is the biggest cause of spoilage so try to removes as much as possible from the jars before sealing them; try to use non metallic lids as these can react badly with the vinegar.
The pickling process should take a couple of weeks, after that they should stay crisp for at least a year if stored in a cool, dark place.