How to Can Jam and Jelly, the USDA Way

Learn the safe way to make jam and jelly, and you’ll have a sweet, convenient treat for months to come!

Jelly Temperature Test
There are two ways to test jelly for doneness. For the temperature test, simply use a jelly or candy thermometer to boil the mixture until it reaches the temperature specified for the altitude where you live. 
Chart From United States Department of Agriculture