Most beef sold in supermarkets today is grain-fed, meaning that after the animals are 6 months old, they are fed a diet of corn and other grains. These grains are cheap and fatten the animals quickly, lowering production costs for large-scale farms and increasing the marbling in the meat. But since cows’ bodies are not designed to digest corn, this type of diet makes them sick, often requiring antibiotics. Grass-fed animals, on the other hand, eat grass and hay, are not fed antibiotics or growth hormones, and are not confined. Grass-fed meat is generally leaner than grain-fed, but after some testing, we discovered that the differences are minimal. Note that because it has less fat, grass-fed beef is less forgiving when it comes to overcooking, so be sure to check the temperature of the meat at the beginning of the time range. The best way to source grass-fed beef, lamb, and bison is to seek out a high-end grocery store or a local butcher shop.