Here's the definition that's on our security deposit page, which doesn't get into the nitty-gritty: Normal wear and tear is a term that Wisconsin law does not define.
(3)Protein Fat-Free Percentage, Protein Fat-Free Content, PFF Percentage, PFF Content or PFF of a product means the meat protein (indigenous to the raw, unprocessed pork cut) content expressed as a percent of the non-fat portion of the finished product.
Since the inception of the Meat Inspection Act of 1906 the law has been expanded to include other kinds of meat products. In 1967 Congress passed the Wholesome Meat Act and the Wholesome Poultry Act which set a minimums sanitation standard for State inspections of meat packing and poultry plants.