Bring boiling-water canner, half full with water, to simmer. Wash jars and screw bands in hot soapy water; rinse with warm water. Pour boiling water over flat lids in a saucepan off the heat. Let stand in hot water until ready to use. Drain well before filling.
Stem and crush strawberries thoroughly, one layer at a time (I use a potato masher for this). Measure exactly 4½ cups of prepared fruit and the balsamic vinegar into a large saucepan (at least 6-8 quarts).
Add the powdered pectin to the strawberries in the saucepan and stir to combine. Add butter (to reduce foaming).
Bring the mixture to a full rolling boil (a boil that doesn't stop bubbling when stirred) over high heat, stirring frequently.
Stir in sugar and return the mixture to a full rolling boil. Continue to boil for exactly one minute, stirring constantly. Remove from heat and skim off any foam with a metal spoon.
Add 1 tablespoon of the fresh ground black pepper and stir to combine. Take a little taste (careful, as it will be hot!) and add more pepper, if desired.
Ladle into the prepared jars, filling to within ¼ inch of the tops. Wipe jar rims and threads.
Cover the jars tightly with two-piece lids. Screw the bands on tightly. Place jars on elevated rack in canner. Lower rack into canner. (Water must cover jars by 1 to 2 inches. Add boiling water, if needed.)
Cover the pot and bring water to a gentle boil. Continue to boil for 10 minutes.
Remove jars and place them upright on a towel to cool completely. After the jars cool, check the seals by pressing the middle of the lids with a finger. (If lids spring back, lids are not sealed and refrigeration is necessary.)
Wash the jars with hot soapy water, rinse well and set on a clean kitchen towel to dry.
Stem and crush strawberries thoroughly, one layer at a time (I use a potato masher for this). Measure exactly 4½ cups of prepared fruit and the balsamic vinegar into a large saucepan (at least 6-8 quarts).
Add the powdered pectin to the strawberries in a saucepan and stir to combine. Add butter (to reduce foaming).
Bring the mixture to a full rolling boil (a boil that doesn't stop bubbling when stirred) over high heat, stirring frequently.
Stir in sugar and return the mixture to a full rolling boil. Continue to boil for exactly one minute, stirring constantly. Remove from heat and skim off any foam with a metal spoon.
Add 1 tablespoon of the fresh ground black pepper and stir to combine. Take a little taste (careful, as it will be hot!) and add more pepper, if desired.
Ladle into the prepared jars, filling to within ¼ inch of the tops. Wipe jar rims and threads.
Cover jars tightly with lids and allow to sit at room temperature, undisturbed for 24 hours then refrigerate or freeze as desired.
See Café Tips above in the post for more detailed instructions and tips to ensure success.
If you prefer to use Metric measurements there is a button in each of our recipes, right above the word “Instructions”. Just click that button to toggle to grams, milliliters, etc. If you ever come across one of our recipes that doesn’t have the Metric conversion (some of the older recipes may not), feel free to leave a comment and I will add it.
This recipe yields 8 8-ounce jars of jam.