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Boiling sugar, crushed pineapple, and pectin together demands continuous attention during the final rolling boil to reach the proper set point without scorching the fruit solids at the bottom of the pan. Precise measurement of the 5 cups of granulated sugar is chemically required because sugar acts as a preservative and structural agent alongside the 4.5 tablespoons of classic pectin, meaning arbitrary reductions will prevent the mixture from gelling.
Freezer tests offer the most reliable method for checking jam consistency without relying solely on electronic equipment. Place two small ceramic plates in the freezer before starting the cook time. Spoon a small amount of the boiling jam onto one chilled plate, return it to the freezer for exactly one minute, and push the edge of the jam with your finger. Wrinkling and holding its shape indicates the gel point has successfully been reached; liquid running flat requires another two minutes of boiling before retesting on the second plate.