According to the Larousse Gastronomique, sweetbread is “the culinary term for the thymus gland (in the throat) and the pancreas (near the stomach) in calves, lambs and pigs.” Larousse further states that thymus sweetbreads are “elongated and irregular in shape” while pancreas sweetbreads are “larger and rounded.”
But sweetbreads are neither sweet, nor are they bread. The word “sweetbread” was first used in the 16th century, but the reason behind the name is unknown. Sweet is perhaps used since the thymus is sweeter and richer tasting than muscle flesh. Bread may come from brede “roasted meat,” or is used because bread was another name for morsel.
Sweetbreads fit into the category of offal, along with other organs, meaning “off-fall” or off-cuts from the carcass of an animal. Sometimes known as variety meats, the heads, tails, and organs of animals have long held a place in European kitchens. In the days before the supermarket (admittedly most of human history) when people butchered their own animals, nothing was wasted from the carcass. Thus many recipes for the nasty bits were created to make the most of these odd, often highly nutritional and tasty cuts. Sweetbreads, aka thymus glands, help young animals fend off disease, and after about six months, they are no longer needed and disappear. So sweetbreads are only found in calves, lambs and kids, with the sweetbreads from milk-fed veal calves being most commonly eaten.
Offal has always had a cult following in professional kitchens, though less so with home cooks until recent years. Sweetbreads are highly prized by chefs for their mild flavor and tender, creamy texture. They are quite versatile and can be prepared many ways: sautéed, poached, grilled, fried, roasted or braised. Sweetbreads are often supporting stars in pâtés, terrines, sausages, cold appetizers, stews and salads.
However they are cooked, sweetbreads must be soaked in cold water for a minimum of three hours, or even up to 24 hours, to remove any blood. Change the water a few times during the soak. Then blanch the sweetbreads—this makes their texture firmer–bring them to a boil in a pot of water and simmer gently for 5 minutes. Place in ice water to cool quickly and then drain. When they are cool enough to handle, take each sweetbread and pick it over, taking off the fatty, gristly, sinewy bits and veins. The trick is to do this without cutting or removing the membrane, though the membrane is removed in some recipes, so the sweetbreads can still be used if the membrane is accidentally broken.
Traditionally, French and Italian chefs serve sweetbreads in rich, creamy sauces, such as veloute sauce or brown sauce, like Madiera, or truffle sauce. Sweetbreads can be served breaded and fried, or grilled after a night-long soak in buttermilk, sautéed, poached or broiled. In the modern renaissance of offal sweetbreads are increasingly being seen on the menus of the nose-to-tail set.