Wash 1 1/2 cups of packed mint leaves. Place in a large saucepan and crush thoroughly with a wooden masher; add 2 1/2 cups water and bring quickly to a boil. Remove from heat, cover and let stand 10 minutes; strain. Measure 1 3/4 cups in a saucepan; add sugar and lemon juice, mixing well. Stir in green food coloring until desired color is obtained (about 10 to 15 drops). Place over high heat and bring to a boil, stirring constantly; add liquid pectin immediately. Taste and add mint flavor if necessary. Bring to a full rolling boil and boil hard for one minute; remove from heat. Skim quickly and pour hot into hot sterilized jars; seal. Yield: 2 (8 ounce) jars.