Here are two methods to tell if your jam is cooked enough:
- Method 1: You can use a sugar thermometer. In theory, when the temperature reaches 104°C/105°C, the jam is sufficiently cooked and ready to be jarred. In practice, I find the readings to be quite variable, depending on the thermometer’s position in the pot. I tend to rely on the method described below.
- Method 2: The "cold plate" method. Pour a small amount of jam onto a plate straight from the fridge. The mixture should form a rounded drop, not run, and wrinkle slightly when pressed with a finger. At this stage, the jam is fully cooked, but you can stop earlier depending on your preference. With this method, you can clearly see what to expect in terms of consistency.