Steamer canning Concord grape juice question
I was wondering how long you normally steam your Concord grapes for juice? The instructions I have say that from the time the steam starts coming out of the lid it should take 60 minutes to get all the juice. If I only steamed the grapes for 60 mintes I would get around 2-3 quarts from a full batch, but if I steam them for around 3 hours I get 5-6 quarts. My elevation is 4500 feet above sea level, so that my have something to do with it, but I am just trying to figure out if I am doing something wrong.