Through the generosity of some friends from church, we received many pounds of grapes, white and purple. I decided to make grape jelly out of these grapes since the rest of the family was not enjoying eating these seeded grapes. After a quick Google search, I became a grape processing professional (Not at all!)
The consensus among grape juice/jelly web sites was to first wash the grapes and pick them over for any bad grapes. Take the grapes off the stems and mash them with a potato masher. I opted to just run them through my food processor the first time. I only had 4 lbs of white grapes, so it didn't take too long. (And these didn't stain when the juice leaked out a little.)
With the concord grapes, I washed and picked them over, then put them all into my big huge stock pot. I didn't want to mash them and then move them and get my entire kitchen all stained, so I mashed them with the potato masher in the stock pot. Some of the grapes didn't get mashed, but they break down as they cook, so I wasn't too worried.
So after your grapes have been squished up, one way or another, put them on the stove in a pot that holds at least twice the volume of the grapes. Turn the oven on to medium high heat to get the grapes up to temperature, stirring occasionally, then turn down to medium-low heat to allow the grapes to break down and release their juice. How long you let them sit really depends on how many you have. When I had 4 lbs of white grapes it took about 15 minutes. When I had 15 lbs of concord grapes, it took about an hour. Anyway, you want to let it simmer for a while to get the juices out of the grape. Stir occasionally to make sure nothing burns on the bottom. (You shouldn't need to stir too much if you're simmering on low.”
Prepare another bowl or pot, big enough to hold all the juice, by wrapping a cheesecloth over the top of the bowl and securing with an elastic band or twine. Let the cheesecloth sag a little if you have a large amount of grapes to strain. Pour the grapes over the cheesecloth and let them sit for at least an hour. I found that I needed to stir them a little every 20 minutes or so to let the juices move around and drip through. I also covered it, just to make sure the fruit flies didn't make their homes in my grapes.
What drips through is the juice that you use to make your jelly. It may form crystals after sitting in the fridge for a day, but that doesn't affect the juice or jelly, so don't worry about the crystals. Different pectins have different recipes, so I can't tell you how much you'll need, but you can always top it up with another kind of clear juice (apple, cranberry, pear, store-bought grape). The first recipe I made, with store-brand pectin, called for ¼ cup lemon juice, 4 cups of grape juice and 4 ½ cups of sugar. The second recipe that I made, with Certo pectin, called for 5 cups of grape juice and 7 ½ cups of sugar. They both tasted great.
If you decide to skip the jelly and just drink the juice, I have to tell you that it is very sweet if you drink it straight up. We ended up mixing it half and half with water and it still tasted just as good (if not better) than the store-bought stuff. It was just too sweet and concentrated straight from the grape!
So there you have it. That's all I've learned about grapes in the last few days. I welcome suggestions and ideas from anyone with more than three days experience in the grape juice/jelly-making business.