The sausage and ground meat recipes discuss the appropriate fat content (and you grind fat separate from lean, etc.). So we want a 20% fat content, but how do we measure that? I could imagine doing some sort of quantitative analysis: grind fine, do solvent extraction, evaporate off the solvent, weigh the fat. But that seems a bit complex.
Or, is commercially supplied meat so consistent in fat content that knowing the cut and grade tells you the fat content sufficiently well? (leaving aside things like trimming). If that were the case, then I suspect that small volume meat producers (e.g. your local 4-H kid) which, while producing meat that is of high general quality, is probably not "standardized".
Do the "official meat inspectors" do this by eye? I can see someone with 20 years of inspection experience being able to just look at a steak and know the fat content.
