To make the juice:

1. Remove the stems, and gently wash and drain the grapes.
2. In a large stainless steel pot, add the grapes and just enough water to cover them.
3. Bring to a boil over medium high heat, stirring and crushing the grapes occasionally, just until the grapes are softened, 5 to 10 minutes.
4. Transfer crushed grapes to a dampened jelly bag set over a bowl.
5. Cover the sides with plastic wrap to avoid any splashing, and let drip for at least 2 hours or overnight to collect the juice.

To make the jelly:

1. Wash jars and lids. Place jars in a big pot filled with water and heat to a simmer (180° F - 80° C). Place the lids after you turn off the water, when the water it's still hot but not simmering anymore.
2. Keep them warm on a baking dish in a 250° F oven until ready to use.
3. In a large stainless steel saucepan, combine the grape juice with the sugar and lemon juice.
4. Bring to a boil over medium-high heat, stirring to dissolve the sugar.
5. Boil hard, stirring frequently, and skimming off the foam, for about 20-25 minutes, or until mixture begins to thicken and have that sheen on top.
6. Quickly pour hot jelly into hot jars, leaving 1/4 inch space from the top.
7. Wipe rim, put lid on and screw tight.
8. Place jars in canner, ensuring they are completely covered with water, place lid on.
9. Bring to a boil and let boil for 10 minutes.
10. Remove lid and let cool for 5 minutes before taking jars out of canner and storing.