I'm not sure why this happens. It seems to be worse when separating the pulp from the skin and not as bad or non existent when you are just taking the grapes off the stems. It goes away after a couple hours and seems to affect some people more than others.
Sam was put to bed and Jamey helped me finish canning 25 quarts of grape juice concentrate. I don't miss the lull at all. Yet.
Grape Juice Concentrate
In a clean, quart jar add 2 cups cleaned, stemmed whole grapes. Pour 1 cup sugar over the grapes. Fill jar, leaving one inch of head space, with boiling water. Cap with a hot lid and jar ring.
The recipe in the Simply in Season cookbook says you do not need to process/hot water bath them, but I have found that they do not all seal unless I do.
I put them in a hot water bath for 15 minutes. Don't be dismayed if it looks like the sugar has all settled on the bottom. It will eventually dissolve.
Wait a month or so before opening- the longer you wait, the stronger the flavor. Since this in a concentrate recipe, you will want to add some water after you have strained out your grapes at drinking time.