This ruby grapefruit jelly is one of the first kanten jellies I learned to make. Once I process the juice, I pour the jelly back into the rind of the fruit, where it sets, making for a dramatic presentation. If you have some goodumeshu (plum brandy) on hand, I suggest adding a few tablespoons to the grapefruit juice. It’s a magical ingredient that will amplify the flavor of the grapefruit juice, making the jelly taste almost like candy. One useful tip is to make sure the juice you are adding is at room temperature. If you add very cold juice, you risk the jelly setting up in the pan, before you can pour it into your grapefruit shells. If you do not have an electric citrus juicer, you can squeeze the juice from the grapefruit with a reamer; avoid citrus squeezers, which will damage the rind.

Excerpt from Rintaro: Japanese Food from an Izakaya in California.