Extracting Berry Juice
Prepare fruit by washing and stemming (or hulling strawberries).
Place the fruit in a pot with a small amount of water. It's usually about 1/2 cup water for every 2 to 4 cups fruit, but see recommendations below based on the specific type of fruit.
Bring the fruit and water to a simmer over medium heat and cook, mashing frequently with a potato masher, until they've completely fallen apart and released their juice (about 5 to 10 minutes).
Strain through a jelly bag or a fine-mesh strainer lined with a double layer of dampened cheesecloth.
Canning Berry Juice
Start by preparing a water bath canner, along with jars, lids, and rings. The canner should be barely simmering (180 F) for a hot pack.
Heat the strained juice to about 190 degrees F over medium-high heat, but do not boil. Turn down the heat to low and keep the juice at 190 F for 5 minutes. Add sugar and stir to dissolve (if using).
Ladle the hot juice into prepared jars, leaving 1/4 inch headspace. Apply canning lids and screw-on rings to finger tight.
Process in a water bath canner for 15 minutes for half-pints, pints, and quarts. Above 6,000feet in elevation, increase canning time to 20 minutes.
After the canning time has completed, turn off the heat and leave the jars in the water to cool slightly for 5 more minutes (to help prevent siphoning), then use a jar lifter to remove the jars to cool on a towel on the counter.
Check seals after 24 hours and store any unsealed jars in the refrigerator for immediate use. Properly canned and sealed jars of strawberry juice will maintain peak quality on the pantry shelf for 18+ months. Refrigerate after opening.