How to safely home can grape juice using the tested USDA method.
Wash and stem grapes.
Put grapes in sauce pan.
Crush with potato masher or similar device.
If there's not enough juice to cover the crushed grapes, add just enough boiling water from a kettle to cover the grapes.
Heat pot to a boil, then lower to a simmer and simmer uncovered for 10 minutes, until the grape skins are soft.
Strain through either a double-layer of cheese cloth, or a jelly bag.
Discard skins and sediment.
Put juice in covered containers in the refrigerator and let stand there for 24 to 48 hours.
Carefully pour juice into a pot, being careful not to disturb the sediment at the bottom of the containers.
Taste the juice cold, see if you want to sweeten it.
If so, do so now to taste.
Heat juice, stirring occasionally, until it comes to a boil.
Ladle hot juice into jars. (See note on special jar sterilization.)
Leave 1 cm (1/4 inch) headspace.
Wipe jar rims.
Put lids on.
Process in a water bath or steam canner.
Process half-litres and litres for 5 minutes; 2 litre (quart) jars for 10 minutes. Increase time as needed for your altitude.
Grape Juice. www.healthycanning.com