Originally posted by AngelZoo
[B]micki: You do not have to add all the fats and such to an extruded food, some companies choose not to, which is perferctly fine, and preferable to some people (such as myself) solid gold is a perfect example.
In comparion to extrusion vrs rendering, extrusion wins hands down, rendering is the cooking method that most companys (think of those found at popular pet stores and grocery stores) use.

Here's a quick little article for anyone whom is interested.

http://business.gorge.net/gorgevet/wysong.htm
See, everything that I've read (and info from my vet) states that the extrusion method was far worse that baking. Here's a direct quote from one of the sites:
"Most dry food is made with a machine called an expander or extruder. First, raw materials are blended, sometimes by hand, other times by computer, in accordance with a recipe developed by animal nutritionists. This mixture is fed into an expander and steam or hot water is added. The mixture is subjected to steam, pressure, and high heat as it is extruded through dies that determine the shape of the final product and puffed like popcorn. The food is allowed to dry, and then is usually sprayed with fat, digests, or other compounds to make it more palatable. Although the cooking process may kill bacteria in pet food, the final product can lose its sterility during the subsequent drying, fat coating, and packaging process. A few foods are baked at high temperatures rather than extruded. This produces a dense, crunchy kibble that is palatable without the addition of sprayed on palatability enhancers. Animals can be fed about 25% less of a baked food, by volume (but not by weight), than an extruded food."

Also, this is what I've read about the rendered fat (not used on all extruded foods, but most):
"You may have noticed a unique, pungent odor when you open a new bag of pet food -- what is the source of that delightful smell? It is most often rendered animal fat, restaurant grease, or other oils too rancid or deemed inedible for humans.

Restaurant grease has become a major component of feed grade animal fat over the last fifteen years. This grease, often held in fifty-gallon drums, may be kept outside for weeks, exposed to extreme temperatures with no regard for its future use. "Fat blenders" or rendering companies then pick up this used grease and mix the different types of fat together, stabilize them with powerful antioxidants to retard further spoilage, and then sell the blended products to pet food companies and other end users.

These fats are sprayed directly onto extruded kibbles and pellets to make an otherwise bland or distasteful product palatable. The fat also acts as a binding agent to which manufacturers add other flavor enhancers such as digests. Pet food scientists have discovered that animals love the taste of these sprayed fats. Manufacturers are masters at getting a dog or a cat to eat something she would normally turn up her nose at."