Since there was an inquiry into Concord grape recipes, I thought I'd post one for grape juice. This recipe was given to me by Donna Flieg, who works for us. She said this recipe came from Linda Ziegler, who got it from Barbra Schwent. It uses old-school-grandma-like-dialect, which I personally thoroughly enjoy. Having a heritage from three major Ste. Gen family names (Flieg, Ziegler, and Schwent), you know this recipe is authentic.
Put grapes in large pressure canner. No more than 2/3 full. Close canner and put weight on. Do not exhaust canner. Bring pressure to 5 pounds. Remove from heat, allow to cool to zero. Line a large pot with an old pillow case and pour hot grapes into it. Hang "bag" and allow to drip. Chill juice to separate crystals in large cartons. Ladle into freezer cartons being careful not to disturb crystals which cling to sides of carton when chilled. Freeze or use for jelly or juice.
Since I am unfamiliar with freezer cartons I asked, and Donna said she uses plastic resealable ice cream containers.