Prepare home canning jars and lids according to manufacturer's instructions.
Jars should be covered with water and boiled 10 minutes to sterilize.
To prepare juice: Put mint leaves in a bowl; add 1 cup boiling water; let stand
1 hour. Press juice from mint leaves, reserving 1/2 cup mint extract, set aside.
Finely chop pineapple.
Add 1 cup boiling water; simmer 5 minutes, covered, stirring occasionally. Crush
pineapple; simmer 5 to 10 minutes. Strain juice through a damp jelly bag or several
layers of cheesecloth. Measure 3 cups pineapple juice.
To make jelly: Combine mint extract, pineapple juice, lemon juice, pectin and
green food coloring, if desired in a large saucepan. Bring to a boil over high heat,
stirring constantly. Add sugar, stirring until dissolved.
Return to a rolling boil. Boil hard 1 minute, stirring constantly. Remove from
heat. Skim foam if necessary. Ladle hot jelly into hot, sterilized jars, leaving
1/4-inch headspace. Wipe jar rim clean. Screw band down evenly and firmly just until
a point of resistance is met fingertip tight.