Making Jam Without a Thermometer

Weigh fruit and sugar; 60 to 70 percent sugar to fruit gives a jam that keeps. Mix them with lemon juice and leave them an hour so the juice runs. Put two saucers in the freezer. Boil the jam hard in a wide pan, stirring often, skimming the foam. After 10 to 15 minutes, drop a spoonful on a cold saucer, wait 30 seconds and push it with your finger. If the surface wrinkles, it's set. Ladle it into hot sterilized jars, seal and turn them over for five minutes. Low-pectin fruit like strawberries takes longer.