While the beets are cooking, combine the sugar, vinegar, pickling salt, lemon juice and clove oil in a large saucepan or pot. Bring to a boil. Pour the hot brine over the beets in the jars to within 1/4 inch of the top. Wipe the rims with a clean towel and seal with lids and rings. Set at room temperature for 24 hours, then store in the refrigerator. Wait a few days before eating to allow beets to soak up the flavor.