Well, I did extensive research and this is what I found. Years ago, it was made from a piece of good meat that has been covered with water and baked till tender. Then pick and shred the meat...make sure it is nothing but meat. No bone. No gristle. No fat. No sinew. Chop the meat up fine. Add in apples, raisons, currents, spices, sugar, suet, vinegar, cider and cook real slow for 2-3 hours. Then you can can it for pies later.
They are also made from green tomatoes...vegetarian. I went to the NONE SUCH web site to see what they put in their mincemeat and couldn't find a list of ingredients. So I would guess it has meat in it too. But it doesn't have to.