Gel Point

The temperature at which jams “set,” which means that they’ve foamed and continued thickening from a loose liquid into a more-viscous, jammier consistency; see Wrinkle Test. Almost universally, jams cook until they reach 220°F [105°C]. If the fruit is low in pectin, it can still not firm up at that temperature, and may need to be taken as high as 240°F [115°C] but 220°F [105°C] is a good place to start.