Canning soups with milk or butter
I've read in countless places that it is dangerous to can homemade soups that contain milk, cream, butter, oil, etc. What I can't seem to find out is why - does anyone know the reason for this?
Most of my soups are basically the same variation on a creamed soup, sometimes containing milk and sometimes not. I sautee the onions, add whatever veggies (summer squash, zucchini, carrots, leeks), then add potatoes and veggie stock, boil it all until it's soft, and blend it. If it's too thick I'll add some more stock or some milk. It generally turns out to be thinner than something like spaghetti sauce, but not as thin as storebought cream soup, because of the potatoes.
Anyway...I just got a pressure canner, and want to know if it would be safe to can this kind of soup, if I should just freeze it like I always have, or if I should alter the recipe in order to can it safely.