Think twice before you spend your hard earned money on sausages and feed them to your family and friends.
The casings of most sausages and hot dogs are made out of dissolved, homogenized cowhides that are then extruded into a solid tube.
Originally, sausages were made by stuffing an animal’s pureed internal organs into its intestines. As sausages shifted from a locally made food to a mass-produced industrial product, it became infeasible to make all sausages with traditional intestine casings.
Some sausages are now stuffed into inedible synthetic casings, but for consumers preferring a more natural-seeming food, an alternative edible casing was needed. Enter collagen, the primary protein that makes up connective tissue in the bodies of humans and other animals.
To make collagen sausage casings, the hides of slaughtered cows are set aside and have their hair removed. The hide is then chopped up and mixed with water, lactic acid and cellulose fibre until it swells into a slurry. A vacuum removes air from the slurry, which is then homogenized, re-vacuumed, and pressed into a thin, flat shape. This casing is then coagulated with salt, plasticised with glycerin and dried until it is needed.
The cheaper end sausages are stuffed with chopped eyes, ears, noses, animals private, unedable parts, intestines, offal etc and flavoured with artificial, toxic flavours to make them taste acceptable.
You are better to pay more and get a meat sausage from a reputable butcher that may be better for you. It is probably still wrapped in cow hide though.
Sources: http://www.askthemeatman.com/what_are_collagen_casings.htm http://www.ehow.com/about_5305009_types-natural-synthetic-sausage-casings.html