Cut off the stem of the pineapple (the fruit must make 600 g pulp), quarter and cut out the woody center lengthways. Peel and finely chop the fruit.
Put the pineapple, lemon juice (freshly squeezed) and whiskey in a saucepan. Mix the sugar with Gelfix and stir into the fruit mass. Let everything boil, stirring constantly. Take it off the stove. Immediately fill the mixture to the brim in prepared jars, close, turn and place on the lid for about 5 minutes.