A full rolling boil means the jam bubbles vigorously and continuously, even while stirring; this is crucial for proper setting., Use fresh or frozen rhubarb; if using frozen, include the juices for best flavor., No need to peel rhubarb; just remove leaves as they are toxic., Use a non-reactive pot such as stainless steel or enamel to prevent flavor changes., Butter reduces foam during cooking; skim foam for clearer jam., Follow pectin package directions carefully for timing and sugar amounts to ensure proper gel., Allow jars to cool and sit undisturbed for 12-24 hours before checking the seals and labeling., Unsealed jars must be refrigerated and consumed within a few weeks.