Crystallized fruit means candied fruit, and candied fruit is synonymous with preserved fruit. Sugar-based preservation -- a technique borne from necessity but now practiced as a luxury -- produces a bite of fruit that satisfies your most ravenous candy craving without losing the fruit's flavor identity in the process. Pineapple -- packed with juice-filled cells and pectin-rich cell walls -- develops the candied texture and consistency with little effort on your part, but it takes about five days for the fruit to exchange its water content for sugar. Barely ripe, fresh pineapple works best for this technique.
Cut the pineapple into 1/2-inch-thick pieces. You can cut the pineapple into rings or bite-sized pieces; both work as long as they're about 1/2 inch thick.
Bring equal parts -- by volume -- sugar and water to a boil in a heavy-bottomed saucepan over medium-high heat; add a tablespoon of light corn syrup to prevent the sugar from seizing. You need enough of the mixture to keep the pineapple submerged, or about 9 cups per pound of fruit.
Adjust the heat to medium. Allow a few minutes for the syrup to cool and add the pineapple. Spread the pieces in an even layer using a wood spoon or other heat-resistant utensil.
Simmer the pineapple for 20 minutes; adjust the heat as needed to maintain a lightly bubbling simmer. Remove the saucepan from the heat and place it on a cooling rack and let it sit overnight; cover the saucepan with plastic wrap after it reaches room temperature to prevent debris from entering.
Simmer the pineapple for 20 minutes the next day -- in the same manner as before -- and let it sit overnight. Repeat the simmering-and-sitting-overnight process four more times. If the syrup reduces below the pineapple, cover it with simple syrup until submerged.
Return the saucepan to the stove and set the heat to medium-high. Simmer the pineapple and syrup until it reaches 235 degrees Fahrenheit, or the soft-ball stage of candy-making.
Let the pineapple and syrup sit overnight once more. The next day, transfer the pineapple pieces to a wire rack set on a baking sheet, spacing each piece about 1/4 inch apart or more. Place the baking sheet in the oven.
Turn on the oven light; the light produces enough heat to raise the oven temperature to about 100 F. Keep the crystallized pineapple in the oven until it feels dry to the touch.
Coat the pineapple in granulated sugar, if desired. Store candied pineapple in an airtight container at room temperature for up to 24 months. If the crystallized pineapple feels soft or discolors during storage, toss it.