Wash the jalapeño peppers and remove the seeds and stems (optional for a spicy taste). Process or blend the peppers into a fine chop using a food processor.
In a large pot or heavy saucepan, combine the peppers, vinegar, sugar, salt, and green food colouring. Over medium-high heat, bring the mixture to a rolling boil. Boil for five minutes, stirring often.
Put the mixture back over high heat and bring it to a rolling boil. Add the pectin and simmer, stirring constantly, for 1 minute. Take off the heat.
Pack canning jars leaving a 1-inch headspace. Add to a water bath and let sit for 10 minutes (the high altitude may require an extension of the processing time). Before serving, let the jelly "gel," or firm, for about a day.
