Robert Sietsema answers the age-old question: What is an organ, anyway?

In Rome it goes by the name of "quinto quarto" — the so-called fifth quarter of the animal, comprising the offal and other variety meats. Concealed in sausages, or even reviled and discarded in some cultures, these tissues constitute a prized part of the culinary arsenal in Rome. But there has always been something a little raffish about eating them here in the U.S., though certain organs like liver, bone marrow, and tripe have recently achieved more widespread acceptance — among chefs at least, who find it stylish to incorporate obscure animal parts into their menus.

What is an organ, anyway? It’s a delimited collection of tissue or tissues, often all in one place and dedicated to a specific biological function. The kidneys, for example, filter the blood to produce urine, while the tongue furnishes our sense of taste, assists in producing speech, and waves chewed food through on its way down the alimentary canal. What are variety meats, then? This term includes organs, but also things like tendon and jowl that are not specifically organs but have achieved fifth quarter status by being rejected by broad segments of the dining public due to unwanted textures or associations, or difficulty of cooking.

In this two-part piece, we’ll first explore several aspects of organs and other variety meats, from the biological functions, to myths and associated tales, to the culinary uses to which they’ve been put. In the second half, we’ll identify those cuisines in which offal (an even vaguer term) may be most readily found, and what dishes to look for.

Blood — Yes, blood is technically an organ, even though it seems odd. Pumped by the heart and transported via veins and arteries, blood ferries nourishment to the body and aids in defense against disease. Blood is colored by hemoglobin, a component of red blood cells that bonds with oxygen to carry it throughout the body, and also removes the carbon dioxide that results from metabolism. Culinary uses of blood — usually from a cow, pig, duck, or chicken — include thickening and coloring stews and soups, and as an ingredient in sausages and puddings. Some cultural groups drink blood straight out of the animal in religious rituals or for reasons of health.

Bone marrow — The yellow and red jelly-like tissue inside bones is known as bone marrow, constituting as much as five percent of the body weight in some animals. While the red bone marrow’s primary function is to generate red blood cells and lymphocytes (white blood cells), the yellow bone marrow is mainly fat. Bone marrow of cattle and pigs has long been important in European cuisines, where special bone marrow spoons were developed in 18th century France and England to scoop the marrow out. In Southeast Asia and China, marrow is more likely to be used as soup thickener, or bones containing marrow cracked open and put in soup so the marrow can be sucked out.

Brain — In both vertebrates and invertebrates, the brain is the center of all cognitive functions, the wheelhouse of the ship, if you will. Known familiarly as "gray matter," the brain achieves the consistency and appearance of pudding in the pigs, sheep, and cows that are the principal sources of culinary brains. In those animals, the organ is wrinkled, bilaterally symmetrical, and lobulated. The brain is composed mainly of neurons and ganglia, and is about 60% fat, making it the fattiest organ in the body. The use of brains as food is more limited than some other organs, though it takes well to fritters and scrambled eggs, and can be pan-sauteed with little or no extra oil added, in much the same way as foie gras. When seared, the outside can become crusty, while the inside retains the texture and wobbliness of custard.

Ear — The ear is a uniquely diverse and complex organ, protruding from the body, but also going inside the skull and interacting with the brain. It has two primary functions: collecting sounds from the outside world and assisting animals in maintaining balance. The first function is assisted by the exterior manifestation of the ear (often called the "outer ear"), consisting of a molded flap of skin given shape by cartilage. This is the only edible portion, and when cooked it can become pleasingly crisp. Ear is particularly popular in China and Mexico, sometimes as a snack.

Eye — The organ of sight has almost no muscle, which is the type of tissue usually labeled meat. Instead, it’s a giant ball of goo — way bigger than expected because little of the organ is visible on the outside of the creature. Over 90 percent of the eyeball is water, mixed with collagen to produce a Jell-O-like consistency. Eyeballs are sometimes seen in Mexican and Korean cooking, and Cajun cooks have been known to use them for their magical properties. Does eating eyeballs improve your eyesight? Probably not, but maybe your second sight.

Face — The face meat of a cow or pig is cheap meat indeed. Consisting of such tissues as cheeks, ears, lips, brow, and sometimes eyelids and eyeballs, these tissues are most often made into headcheese (aka "brawn"), which has been popularized in the current era in warm form by Mario Batali and others. Before that, it was mainly a cold luncheon meat found in Eastern European meat cases. Head cheese is made by long-boiling the whole head; connective tissue and bone provide the natural jelly to glue it all together.

Foot — "Give me a pig foot," sang Bessie Smith, "and a bottle of beer," articulating the appeal of this pickled bar snack for the cuisine of the American South. Usually including the actual foot — bone and all — plus part of the shank, the foot of the pig, chicken, cow, sheep, and goat is not an organ but a variety meat, including muscles, ligaments, skin, and tendons. While smaller examples can be gnawed on as snacks, more common usage is found in the foot’s broth-generating properties, used in terrines and soups (in Japan, ramen especially), and valued for its gelatinous properties and its collagen, supposedly good for the skin.

Gizzard — The gizzard is a type of stomach, often one of several in birds, fish, worms, and dinosaurs. Its purpose is grinding up morsels of food rather than sloshing them around with stomach acids. Often, the gizzards contain gravel or other grit to aid in the grinding action. Gizzards are extremely muscular and usually take lots of cooking. The most important gizzard is the chicken’s, which is featured in fried chicken ensembles or eaten by itself either fried or baked. Turkey gizzards are consumed in roasted or pickled form. Gizzards of chickens and turkeys are also important components of stuffings, though they don’t come in the Pepperidge Farm package; they must be added from that little wax-paper package of organs found inside the bird.

Heart — Most meat that we eat is actually muscle, and the heart — which circulates the blood through the mammalian body — is an extreme form of edible muscle. Why extreme? Well, the heart is stronger and more fibrous than any other muscle, which means it must be tenderized or long-chewed when eaten. It is especially popular in South America as street food, often marinated and then cooked over charcoal as kebabs and eaten with chile sauce. Chicken hearts are similarly skewered in Japanese restaurants. Heart meat is high in protein and such nutrients as iron, selenium, phosphorus, zinc, and amino acids, according to Men’s Fitness.

Intestines — The large intestines of pigs, commonly known by the rather unlovely name of bung, can be 30 feet in length, but typically only the last two feet — uniform in width — are used. These form the casings of large sausages in Western gastronomy; in parts of Asia, including China, this bung is eaten by itself, usually boiled for an hour or so and fried, sometimes stuffed, sometimes not. Typically, bung is cut into one-inch lengths before this type of use. Needless to say, the intestines must be very well cleaned before cooking, and are often turned inside out for this purpose. Kidney — Shaped and colored like a huge red bean, the kidney is an organ that filters the blood, removing water-soluble wastes, and adjusts the homeostatic balance of nutrients in the circulatory system; animals typically have two of them. Its byproduct is urine, which flows out of the body through a pair of ureters.

Kidneys are particularly popular as food in European nations such as England, France, Spain, and Sweden, where the most common cooking method is grilling and the flavor is concealed beneath sauces made with mustard and sherry. Chinese cooks stir fry them with other powerfully flavored ingredients. The downside of kidneys is that they frequently taste a little like pee. The upside is flesh that is bouncy like a rubber ball.

Liver — Like the kidney, liver is a filter organ that removes poisons from the body, but also synthesizes hormones and other chemicals needed for digestion. It dwells in the upper abdomen and contains several flap-like lobes. Calf liver is the most popular, but chicken, goat, lamb, and pork liver are also avidly eaten. The texture of the liver is crumbly and yielding, and is one of the few organs sometimes eaten rare or raw. Fish liver sashimi is popular in Japan. According to an elderly friend, liver was so despised during the Great Depression that American butchers gave it away free of charge. This may have served to popularize it, because now it is probably the most popular organ.

Lungs — The USDA has outlawed the eating of lungs in this country since 1971 for a variety of reasons, one of which is the slight potential of the organ transmitting tuberculosis or other pulmonary diseases via the phlegm that accumulates in the lungs of slaughtered animals. The lungs — every mammal has two of the them, which hang like gunny sacks in the chest cavity — are the means by which organisms intake oxygen and eliminate carbon dioxide. They are an important component of the Scottish national dish, haggis, and are often used in Italian cooking, where they are valued for their spongy texture.

Penis — Though it sometimes behaves like one, the penis is not a muscle; indeed, an erection is a hydraulic phenomenon by which the organ becomes engorged with blood. Its purpose is the impregnation of the female of the species during coitus, and the passage of urine that arrives from the kidneys. The penis is gristly in mouthfeel and without any flavor. Its most common usage is in Chinese and Korean cooking, wherein it is eaten to enhance the male libido rather than for any culinary properties.

Skin — Yes, the skin is an organ! In fact, pound for pound, it’s the largest organ in the mammalian body. It consists of three layers: the epidermis, dermis, and hypodermis (which is mainly fat). It functions as protective coating for the animal, but also helps to regulate body temperature. The skin can be eaten attached to underlying flesh, as in Chinese roast pig or Bolivian pig foot escabeche, or detached and cooked separately, as in the chicharrones prized in Mexican and other Latin cuisines.

Spleen — A zoology teacher in college once told her class, "The spleen is just a bag of blood," and indeed it is. While it once had more important functions in invertebrates, it now acts as a blood reservoir, and has anti-bacterial properties that make it function as a giant lymph node. It also metabolizes used red blood cells and salvages the components. Sicilians are particularly fond of spleen, and make it into little focaccia sandwiches called vasteddi or pani ca meusa. It’s a regular ingredient in French pot au feu. Apart from that, it is most often found as a component of sausages or sunk into pet food.

Sweetbreads (thymus) — Sweetbread is one of the most confusing terms in the offal lexicon. Usually pluralized, the term can refers to at least two completely disparate organs, both of which most commonly come from young animals such as calves or lambs. The thymus is one type of sweetbread, a bi-lobed gland that lies behind the breast bone and manufactures T cells. It is sometimes called "neck sweetbreads" and is high enough in fat that it can usually be sautéed with no extra oil once the exterior membrane has been removed. It is highly prized in French cooking and has enjoyed a vogue in American restaurants for the last decade or so. Argentines and Turks are fond of grilling sweetbreads over charcoal.

Sweetbreads (pancreas) — Sweetbread can also refer to the pancreas, a gland that hides behind the stomach, and is thus sometimes called "belly sweetbread." Manufacturing insulin and other hormones that aid digestion is the organ’s biological function. Shaped like a handgun, pancreatic sweetbreads sometimes end up in head cheese, but more often they’re breaded and fried or grilled over charcoal. Rabbits have no pancreas, but most vertebrates do. Other tissues sometimes described as sweetbreads include testicles, the parotid (salivary gland), and a series of secretory glands under the tongue.

Tail — The porcine tail is a popular foodstuff in many cultures, and is particularly cherished in Ontario. It can be pickled or smoked, but when boiled produces animal gelatin of the type used to glue headcheese together, or to form a stock for ramen. Mainly composed of skin and cartilage, and constituting a corkscrew in shape, it is a prize tidbit that often goes to the pitmaster in barbecue restaurants.

Tendon — This is the tissue that attaches muscles to bones. It is fibrous and partly composed of collagen, which makes tendon great for thickening soups. It is common is Asian cuisines, being a frequent ingredient in pho, and slicked with oil and ma la peppercorns in Sichuan cuisine. The variety meat displays a rubbery and jellylike consistency, and benefits from long cooking. When you pull a hamstring while jogging, you are injuring a tendon.

Testicles — The testes of an animal primarily function in producing sperm for the purposes of reproduction. They often hang outside the body in order to maintain a lower temperature than the body. Rocky mountain oysters are a euphemism for bulls’ testicles, valued as food in certain cattle-producing Western states, and they are known as lamb fries when referring to the testicles of baby sheep. In culinary usage, testicles are surprisingly tender and luscious, like a well-marbled steak.

Tongue — The glottal organ can go two or even three ways. It can be jellied and sliced thin as in Jewish beef tongue, which retains its bouncy and somewhat tough quality; it can be simmered into oblivion in chile sauce as is done in Mexican cuisine with goat and beef tongues; or it can be stir fried in Chinese cuisine, for which veal tongues and duck tongues are often employed. The human tongue is the organ that, along with the eyes and nose, most helps you enjoy your food via the taste buds which coat its upper surface.

Tripe (stomach lining) — Like sweetbreads, tripe is something of a catchall term. Most commonly it refers to the stomach lining of various farm animals, most especially the cow. This is called honeycomb tripe for its resemblance to a honeycomb. When thoroughly soaked before cooking, often in milk, it achieves a sparkling white appearance. To the extent it is cleaned, tripe has a neutral flavor that takes to many sauces. When not well-cleaned (which some cultures prefer), it tastes a little skanky. Latin cultures feature it in the soup called mondongo, while Turks use it as a hangover remedy in the soup iskembe corbasi. In fact, soup is the most common way to feature tripe, especially in the Balkan countries.

Tripe (small intestine) — In Chinese cuisine, tripe is more likely to refer to the small intestines, which are most frequently braised or stir fried. These are ubiquitous on unreconstructed Chinese menus in America. The intestines are of small circumference like drinking straws, long and rubbery. They make a prominent appearance in African-American food in stewed form as chitterlings, and in Argentine cuisine as a popular charcoal-cooked item in a mixed grill.

Uterus — The uterus (often hilariously pluralized in groceries and restaurants as "uteri") is readily found in Chinese supermarkets in the U.S., though more rarely seen in restaurants, making it more of a home-style dish. Its purpose zoologically is as a haven for the developing embryo or embryos prior to birth. The Vietnamese soup chao long contains it (along with other organs), wherein it presents a very chewy consistency and cooks up gray and somewhat hard. Remember, the uterus is mainly muscle. Uterus is also used in Thai cooking, most often immersed in red coconut curry.