Cardamom Grape Jelly

3 1/2 lbs concord grapes
1 1/2 cups water
1 (1 3/4 ounce) box dry pectin
7 cups sugar
3 teaspoons ground cardamom

Cook grapes in water in a covered saucepan.
Strain mixture through cheesecloth.
Measure 5 cups of the juice and pour into a 5-quart kettle.
Add the pectin and cook over high heat, stirring constantly, until the mixture comes to a full, rolling boil.
Boil rapidly one minute, stirring constantly.
Add sugar and cardamom and boil rapidly again for one minute.
Remove jelly from heat, skim off foam, and pour into hot sterilized jars, leaving 1/2-inch space at the top of each jar. Process in water bath for 10 minutes.