Wash and drain the grapes and remove from the bunches. Set aside 1 pound.
Crush the remaining 3 pounds and combine with water and the jalapeño in large saucepot. Bring to a boil, add sugar and simmer for 1 minute.
Strain juice through three layers of cheesecloth or a damp “jelly bag”. Discard solids.
Measure out 4 cups of juice and add pectin. Bring to a boil, and remove from heat.
Slice remaining 1 pound of grapes in half. Distribute halved grapes evenly to each jar.
Ladle the juice into each jar, cover with lids and seals and process in boiling water for 10 minutes.
Let cool at room temperature overnight, then tighten jars. Label and date the jars. Can be stored unopened at room temperature for 12 months. Refrigerate after opening.