Wash the pineapples thoroughly. Peel off the tough outer skin and remove the spiky eyes with a paring knife. Remove the core, then slice or cube the pineapple into bite-sized pieces. Set aside the cores for juice.
To create your own juice, simmer the cores in a saucepan with enough water to cover them. Let it simmer for 10 minutes, then strain the mixture. Add sugar if desired. For the recommended extra light syrup, use 6 ½ cups of juice and ¾ cup of sugar for a 9-pint batch.
In a large saucepan, add the prepared pineapple pieces to your chosen syrup, juice, or water.Heat the mixture to a simmer and cook for 10 minutes to help soften the pineapple and eliminate air pockets (this is key to keeping the fruit intact during canning).
While the pineapple is simmering, sterilize your canning jars. Ladle the hot pineapple pieces into the jars, leaving ½-inch headspace. Pour in enough of the hot syrup or juice to cover the fruit, again leaving the ½-inch headspace.
Wipe the rims of the jars with a clean cloth to ensure there is no food residue. Place the lids on top and secure them with canning rings, tightening them just until fingertip-tight (don’t overtighten, as this can affect the seal).
Fill a boiling water canner with water and bring it to a rolling boil. Carefully lower the jars into the canner and process them according to the altitude chart below. Standard process times for below 1,000 feet in elevation are 15 minutes for pints and 20 minutes for quarts.
After processing, carefully remove the jars from the canner and allow them to cool on a towel-lined surface.
Once cool, check the seals by pressing down in the center of the lid—if it doesn’t pop back, the jar has sealed properly.