In part 1 on this topic we talked about the process of making dry pet food. Let me briefly summarize, so that you don’t have to go back to the original comment:
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.
Most semi moist foods are manufactured in a manner similar to dry foods, with a few differences. The product is formulated, mixed, and passed through an extruder just like dry food. The extruders are configured at a lower temperature and pressure than dry foods. After leaving the extruder semi moist food instead of drying goes through low agitation coating drums where water, chemicals that help to maintain moisture (humectants), and acids are added. After that the food goes into a refrigerated cooler to set the structure so it will maintain a higher moisture content and spongy texture. Semi moist foods with 25% to 35% are higher in moisture than dry foods with typically around 10%. This also means that they are therefore more exposed to spoilage from mold and bacteria. Additionally, the high moisture content also makes this type of food susceptible to loss of moisture and texture deterioration. To address these issues, semi moist foods are formulated with mold and bacterial inhibitors and packaged in special moisture proof bags.
The French army developed the processing of canning food back in the good old days of 1809. Since then, the process has made many improvements to improve quality. However, the basic principles still to this day are the same. Sealing a food product in a can and then heat sterilizing it continues to be one of the most common and affordable ways of preserving food products.
Most canned foods contain a high level of meat products as their base. Fresh and frozen meat and meat by-products are delivered in frozen or refrigerated truck loads. The meat product is ground into small pieces and then carefully weighed and added to a batch mix that may include grains and definitely includes minerals and vitamins as required by their nutrient profiles. After combining the ingredients they go into the mixer where they are thoroughly blended. During this process the temperature is increased and the starch in the food begins to gelatinize. At the same time the protein begins to denature, which improves texture and flavor. Foods that contain carbohydrates generally require a higher temperature to fully cook the starch. Once the product has been properly cooked, it then moves on to the canning process. While the cooked mixture is still hot, the product moves into the filler and seamer machine. This machine fills, places the lids on, and seams from 300 to 600 cans a minute. Steam is blown over the top of the filled can as the lid is applied to maintain the heat, so that when the can cools, it will be vacuum sealed to help prevent spoilage. Once the cans are filled and sealed, they move into the sterilizer where they are heated to temperatures of 121° Celsius for at least three minutes to ensure that any dangerous bacteria are killed. Finally, once the cans have been sterilized, they are cooled, and labeled.
Understanding the manufacturing process of commercial pet foods can help you to choose the best type of food for your cat or dog. Once you choose the type of food you wish to feed, you can pick a quality manufacturer and then closely examine the product line and the individual ingredients to determine the most nutritious and palatable food for your pet.
Ingredients are similar for wet, dry, and semi moist foods, although the ratios of protein, fat, and fiber may change. A typical can of ordinary cat food reportedly contains about 45 to 50% meat or poultry by-products. The main difference between the types of food is the water content. It is impossible to directly compare labels from different kinds of food without a mathematical conversion to dry matter basis.
While the manufacture of pet food can seem complex, it is actually very similar to the way human food is manufactured. Reputable manufacturers go to great lengths to provide a consistent, nutritious product that meets all of a pet's nutritional needs.
The problem with these impressive processes of pet food manufacturing is the processing of the ingredients. One of my favorite experts, Dr. Wysong, D.V.M. calls it “food torturing”. Because it’s done behind the scenes, you don’t see it and it is kind of not so pretty. In his “The Truth about Pet Foods” book he concludes: “What happens between the farmer’s field and the commercial package significantly vitiates healthful nutrition. Unfortunately this dangerous middle is by and large ignored. Once foods are milled, fractioned, blended, extruded, pelleted, dried, retorted, baked, dyed, breaded, fried, sauced, gravied, pulped, strained, embalmed, sterilized, sanitized, petrified to permit endless shelf life, and finally prettified, they become something entirely different from the wholesome starting materials. The vast majority of modern foods are inert and anonymous processing concoctions of a few base ingredients… the resulting myriad products are nothing more but nutritional shells of the real thing.”