I've got a box of peaches and I want to make jam. Most of the recipes I've looked at are pretty straightforward, but what is pectin, and why do they call for so much sugar—like five cups of sugar for four cups of peaches? WTF? My peaches are already almost too sweet.
A: Pectin is a thickener used in most jams. Unlike gelatin, which is often made from animal tissue like horse hooves, pectin is a plant-based molecule that's important in supporting cell structure and is usually derived from processed apple, orange and beet material. Pectin comes in powdered and liquid forms, which have different characteristics and behaviors.
Sugar activates the pectin and makes it do its thickening thing, so the balance of fruit, pectin and sugar determines whether you get peaches in syrup or peach jam. Messing with that balance by, say, using less sugar than a recipe calls for can take you into uncharted territory.