Wrinkle Test

Another way to tell if jam has set (see “Set,”). Place a plate in the freezer. When it is cold (and you think your jam has cooked to the right point), place a tablespoon or so of the jam on the cold plate and let it sit for a couple of minutes to cool. Then nudge the pool of jam with your finger and see if it wrinkles. If it does, the jam will be thick when it cools. If it doesn’t, keep cooking the jam, return the plate to the freezer, and test again in 10 minutes.