The taste, cooking aromas and mouth-feel of fats are crucial to the lure of carnivorousness. In addition, the fats are what help us tell, say, lamb from beef. There are two main kinds of fat in meat, explains Richardson. Triglycerides make up, he says, "the white stuff you can see – the strip around your beef steak or the little white flakes within it," and they are higher in saturated fats. Phospholipids, on the other hand, you can't see because they live in cell membranes and contain the healthier, unsaturated fat varieties. If you extract the triglycerides from meat, says Richardson, "you still get the flavour difference between the species, but if you take the phospholipids out, you start losing the species difference." Lamb, for instance, has a more complex flavour than beef because its fatty acid mix is different. Fat is also responsible for grass-fed animals tasting stronger than grain fed. Grass-fed animals produce omega-3 fatty acids, which – other than being an essential nutrient for us – produce a denser flavour.
In beef there's a subtler difference between grass- and grain-fed but in lamb the contrast is marked. Everyone agrees that grass-fed lamb is more flavoursome, although in countries where grain-fed lamb is more common, such as Spain and North America, the muted flavour is preferred. Whereas mostly grass-feeding countries (England, New Zealand, South America) love the strong lambiness they're used to.