Domesticated animals are grown and slaughtered for meat for human consumption. Normally, only 30 to 40% of the animal is utilized for human food (meat cuts, edible offals, processed meat products). In monetary terms this represents by far the most important product of meat processing plants. However, economics of operating the meat slaughter plant, together with the cost of pollution abatement and/or disposal of inedible material from the slaughter operation, demands that the rest of the material produced from the slaughter operation be used profitably. In most countries everything produced by or from the animal other than the dressed carcass is considered a by-product. Another name for by-products is coproducts. The term "co-product" is coming into common acceptance, to indicate that these materials are contributing to process profitability. In some countries the terms "offal" and "by-product" are interchangeable. Hides and pelts are obvious byproducts and are discussed elsewhere. A partial, but not all-encompassing, list of animal by-products is given in Refs. 1-4.
Many products can be made from the nonmeat parts of the animal (Fig. 1), and various by-products often contribute significantly to the meat plant's profitability. In some instances the commercial value of these by-products is often higher than the sum of the running expenses and the margin required for the meat plant to operate profitably.
Also, because there is a worldwide shortage of animal protein, it is essential to maximize the use of these raw materials. This applies both to products used directly for human consumption and to protein-containing material that can be processed and fed back to animals.
By-products are usually classified as "edible" or "inedible." Edible by-products, such as heart, liver, tongue, oxtail, kidney, brain, sweetbreads, and tripe, that are segregated, chilled, and processed under sanitary conditions are called "variety meats" (or in some countries, offals). Chitterlings and natural casings (intestines) and fries (lamb or calf testicles) can also be eaten. In some countries, the blood and/or blood fractions from healthy animals, processed hygienically under conditions specified by the appropriate regulatory authority, can be an edible byproduct. Some by-products must be processed or refined before they can be eaten. Examples include stomachs for tripe, bones and skin pieces for gelatin manufacture, and fatty tissue for edible fat. Most noncarcass material, if cleaned, handled, and processed in an appropriate manner, could be edible.
There is a sizable international trade in edible byproducts because they are a very economical source of high-quality protein and fat. Custom, religion, palatability, and reputation of these products usually limit their use for human consumption. How a meat processor classifies a specific product depends both on the possible utilization of that product and the availability of a potential market. For example, many potentially edible by-products are downgraded to an inedible use because a profitable market does not exist. Many animal by-products are often underused. Their effective utilization depends on having a practical commercial process to convert the animal by-product into a usable commodity, actual or potential markets for the commodity produced, a large enough volume of economically priced raw material in one location for processing, a method for storing perishable material before and after
Hide Carcass Blood Casings Soft and Paunch and or pelt
Boning hard offals gut contents
Edible Petfood Inedible
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