To begin, prepare your jelly jars and canning equipment. Always start with freshly washed tools, jars, etc.
Remove the seeds and stems from the washed jalapeño peppers. Weigh them to make sure you have 12 ounces of the peppers.
In a blender or food processor, puree the peppers with the vinegar until they are smooth. Pour the mixture into your non-reactive pot. Add the sugar and bring the mixture up to a rolling boil, and boil (while stirring) for 10 minutes.
Add the pectin and butter (see note below) and bring it back to a rolling boil.
Boil hard and stir for 1 full minute. Test to make sure it gels (see the video for tips.) Remove it from the heat.
Ladle the jelly into hot jars leaving 1/4 inch head space.
Remove any bubbles with a bubble wand, then wipe the rim of the jars with a damp cloth dipped in white vinegar.
Place a lid and ring on the jar and place the jar in the hot water bath or steam canner. Do this with all of the jars.
Process the jars for 10 minutes. (See the note about adjusting time for elevation in the article above. Processing times for canning recipes are always give for under 1000 ft elevation. You must make adjustments if you live at a higher environment.)
After the jars have processed, turn off the heat. If using a hot water bath canner, go ahead and remove the lid and let the canner rest for 5 minutes. If using a steam canner, leave the lid on while it rests 5 minutes. Only then remove the lid afterwards.
Transfer the jars to a lined surface in a draft-free location and let them sit for 12-24 hours. You can cover your counter with folded kitchen towels, or use canning mat or a cooling rack.
Remove the rings, test the seals, wash and label the jars. Store them away in the pantry.
Enjoy your homemade jalapeño jelly!
Notes
Butter helps prevent the jelly from foaming up. It will foam while it is actively boiling, but then the foam goes away as soon as you remove it from the heat to jar it up. This is a safe and effective method. If you do not wish to add the butter, you will need to skim the foam from the jelly before jarring it up.NOTE: My jelly recipe does not contain any food coloring. If you wish to have that classic "lime green" color, you will want to add a little green food coloring when you add the pectin. I am not a fan of food colorings, so I just go with the natural olivey color of the peppers.