Stir for the recommended amount of time and carefully scrape sides of bowl to catch all stray sugar granules. Warming jam with sugar crystals may help redissolve the sugar. If you have a microwave, use it to heat the mixture. This will help maintain the bright color and fresh taste of a freezer jam. The cause of pectin crystals may be the use of too much underripe fruit.
Underripe fruit has more pectin than ripe fruit.
The combination of commercial pectin with that in the underripe fruit is more than is needed. Warm the mixture to redissolve the crystals or strain them out. To prevent pectin crystals , make sure the fruit is ripe but not overripe. To prevent crystals resulting from chemical interactions, warm the jam to redissolve the crystals or strain them out. The crystals are harmless, but may be unsightly.