The machinery of the red or white muscle fiber is much the same no matter what the animal, because it has the specific job of generating movement. Fat cells, on the other hand, are essentially storage tissue, and any sort of fat-soluble material can end up in them. So the contents of fat tissue vary from species to species, and are also affected by the animal’s diet and resident gastrointestinal microbes. It’s largely the contents of the fat tissue that give beef, lamb, pork, and chicken their distinctive flavors, which are composites of many different kinds of aroma molecules. The fat molecules themselves can be transformed by heat and oxygen into molecules that smell fruity or floral, nutty or “green,” with the relative proportions depending on the nature of the fat. Compounds from forage plants contribute to the “cowy” flavor of beef. Lambs and sheep store a number of unusual molecules, including branched-chain fatty acids that their livers produce from a compound generated by the microbes in their rumen, and thymol, the same molecule that gives thyme its aroma. The “piggy” flavor of pork and gamy flavor of duck are thought to come from intestinal microbes and their fat-soluble products of amino-acid metabolism, while the “sweetness” in pork aroma comes from a kind of molecule that also gives coconut and peach their character (lactones).