1 to 3 Texas Ruby Red or Rio Star grapefruit
1 1/2 cups water
1/8 teaspoon baking soda
5 cups granulated sugar
1/2 (6 ounce) bottle liquid fruit pectin
Remove skins in quarters from grapefruit and lemon. Set fruit aside. Lay quarters flat; shave off and discard almost all white part.
With a sharp knife or scissors, slice rind very thin. Combine rind, water and baking soda in large saucepan. Bring to a boil and simmer, covered, 20 minutes, stirring occasionally.
Chop peeled grapefruit and lemon; discard seeds. Add to cooked rind and continue simmering 10 minutes.
Measure 3 cups fruit mixture into large saucepan. Add sugar to fruit in pan; mix well. Place over high heat; bring to a full, rolling boil, stirring constantly. Boil hard 1 minute.
Remove from heat and stir in pectin at once. Skim off any foam. Stir and skim 7 minutes. Ladle into hot sterile jars and seal.