Traditionally, casings are made of animal intestines though are now often synthetic. Some sausages are cooked during processing, and the casing may be removed at that time. Sausages may be preserved by curing, drying in cool air, or smoking

History

It is believed that sausages were invented by Sumerians in what is present day　Iraq, around 3000 BC.Fact: date=September 2008 Chinese sausage làcháng (臘腸/腊肠), which consisted of goat and lamb meat, was first mentioned in 589 BC. Homer, the poet of Ancient Greece, mentioned a kind of blood sausage in the Odyssey (book 20, verse 25), and Epicharmus (ca. 550 BC – ca. 460 BC) wrote a comedy titled The Sausage. Evidence suggests that sausages were already popular both among the ancient Greeks and Romans, and most likely with the non-literate tribes occupying the larger part of Europe.

Sausage in Italy has its roots in Lucania, the actual Basilicata. Philosophers such as Cicero and Martial stated a kind of sausage called "lucanica", actually widespread in Italy, was introduced by Lucanian slaves during the Roman empire. During the reign of the Roman emperor Nero, sausages were associated with the Lupercalia festival. The early Catholic Church outlawed the Lupercalia Festival and made eating sausage a sin.Fact: date=May 2008 For this reason, the Roman emperor Constantine banned the eating of sausages. Fact: date=May 2008 Early in the 10th century in the Byzantine Empire, Leo VI the Wise outlawed the production of blood sausages following cases of food poisoning.

Traditionally, sausage casings were made of the cleaned intestines (or stomachs in the case of haggis and other traditional puddings) of animals. Today, however, natural casings are often replaced by collagen, cellulose or even plastic casings, especially in the case of industrially manufactured sausages. Additionally, luncheon meat (such as Spam) and sausage meat are now available without casings in tins and jars.

The most basic sausage consists of meat cut into pieces or ground and filled into a casing such as an animal intestine. The meat may be from any animal, but traditionally is pork, beef or veal. The meat/fat ratio is dependent upon the style and producer, but in the United States, fat content is legally limited to a maximum of 30%, 35% or 50%, by weight, depending on the style. The USDA defines the content for various sausages and generally prohibits fillers and extenders. Most traditional styles of sausage from Europe and Asia use no bread-based filler and are 100% meat and fat (excluding salt and other flavorings, such as herbs). In the UK and other countries with English cooking traditions, bread and starch-based fillers account for up to 25% of ingredients. The filler used in many sausages helps them to keep their shape as they are cooked. As the meat contracts in the heat so the filler expands.