This recipe uses one box of traditional fruit pectin. If you make a lot of jam, you may want to buy pectin in a multi-use container. Follow the instructions on the container for the amount that equals one box of pectin. Pie cherries or sour cherries make the best jam.
Put six clean, 1 cup jam jars into a large pot of water. Bring to a boil and reduce to low to keep the jars and the water hot.
Put six new lids in a small saucepan of water. Bring to a simmer, reduce heat to low and keep warm.
Pit the cherries.
Put the cherries in a food processor and pulse until finely chopped. There should still be bits of fruit visible.
Measure four cups of chopped cherries.
Combine the chopped cherries and pectin in an 8 quart saucepan.
Over high heat, bring the cherry mixture to a full, rolling boil; one that cannot be stirred down.
Add the sugar all at once.
Stir and bring the mixture to a full rolling boil as quickly as possible. Boil for one minute.
Remove the jam from the heat.
Skim off any foam.
Remove the jars from the hot water. Turn the heat to high and bring the water to a boil.
Ladle the jam into the hot jars filling to ¼ inch from the top.
Put a lid and a band on each jar. Tighten until you just meet resistance. The lid must be loose enough to allow air to escape (but not allow water to enter) otherwise the jar will explode when being processed.
When all the jars are full, lower them into the boiling water.
Return the water to a boil and boil 10 minutes at sea level. If you are above 1000 feet in elevation, increase the processing time by the amount noted below.
Remove the jars from the boiling water and tighten the lids. Do not overtighten or you may break the seal.
Allow the jars to cool completely.
When cool, the lids should all be concave or, if pressed, should stay concave. If the lids pop up in the center, refrigerate that jar as the seal is not adequate to protect the contents.
Add the following time to the original 10-minute processing time based on altitude: 1000-3000 feet above sea level: 5 minutes; 3001-6000 feet above sea level: 10 minutes; 6001-8000 feet above sea level: 15 minutes; 8001-10,000 feet above sea level: 20 minutes