Fill the bottom layer of a 3-piece steamer with water. Put washed grapes in the top of the steamer. Cover with lid. Cook on medium heat on stovetop until juice starts to accumulate in the middle portion of the steamer.
When enough juice has accumulated to fill a jar, hold a canning jar with an oven mitt under the drain valve on the center portion of the steamer. (Or alternatively, put the jar on a stool below the steamer so that the hose reaches into the jar.) Open the value and allow juice to fill jar. Leave 1/4 inch headspace for pints and quarts.
Continue steaming the grapes to remove all the juice, and fill jars as juice accumulates. Frequently and carefully check the bottom layer of the steamer to refill water as needed.
Process jars in a boiling water bath for five minutes.
1 bushel grapes makes 15-20 quarts concentrated juice. Drink concentrated, or dilute with water or seltzer and sweeten to taste.