Note: If you have never canned before, I highly recommend Joy of Cooking: All about Canning and Preserving and the Ball Blue Book of Preserving. These books will help you learn about safe canning practices and the equipment you will need.
To me, the most important thing about making jelly successfully is following the measurements. If the measurements below don’t match the recipe on the package of pectin, follow that recipe instead to get your jelly to set properly. I’ve made jelly in the past that doesn’t “jell” and remains a liquid, and it’s mostly because I tried to sneak in more juice than the recipe calls for.
Start by crushing 4 quarts of hulled strawberries with a potato masher in a large pot. Cook for about 5 minutes.
Strain the berries using a jelly bag or cheesecloth. Let the juice drip into a bowl for an hour or more. You can save the berries to make fruit leather.
When the berries have drained, sterilize jars by boiling them in a large pot of water for 10 minutes. Let them sit in the steaming water until you are ready to use them.
Measure out 3 1/2 cups of strawberry juice. If you have extra, you can freeze ice cubes of the juice, which are especially good in lemonade.
Slowly stir in 1 package of powdered pectin, and start heating the juice over high heat.
Add 1/2 tsp butter to help keep the mixture from boiling over.
Bring the mixture to a rolling boil for 5 minutes.
Then add 4 1/2 cups of sugar, and stir to dissolve. Continue to heat the mixture over high heat.
Boil hard for 1 minute.
Skim off any foam, then ladel into the sterilized jars leaving 1/4 inch headspace. Place caps on and screw on rings. If you have a half-full jar, cap it and use it right away, storing it in the fridge.
Return jars to the hot water. Bring to a boil, and process for 10 minutes. Remove jars to a towel or cutting board and allow them to cool, undisturbed, for about a day.
Label jars and store them in a dark place. Yield: about 6 1/2-pint jars.