Pet food is divided into various basic types. These include dry, semi-moist or intermediate moisture, into frozen dessert types and canned. The dry pet food is also known as kibble and there is a fourth category called treats.
Globally, the pet food industry is worth something like $60 billion which puts it in the same league as snackfoods.
The manufacture of pet food is similar to human food processing. It is a highly regulated process. In terms of processing, all hygiene requirements must comply with Annex II of EC Regulation 183/2005. This annex details all the requirements relating to facilities and equipment, people, quality control, storage etc.
The European Pet Food Industry Federation have produced a Guide to the Good Practice for the Manufacture of Safe Pet Foods. This contains some useful information and guidance to help you follow the law and produce safe pet food.
A canned pet food for example is produced the same way as any other although the raw materials might be different. All ingredients should be fresh and suitable for consumption.
Moist and Canned Pet Foods
Foods which are moist and usually canned have a texture and water content similar to fresh meat. They are designed to replace fresh joints of meat or meat pieces. They have a extremely high palatability and appeal to cats and dogs. Because of their high moisture content, they must be preserved by heat sterilization usually through canning. Cans are tinned steel but heat resistant pouches have come to the fore. Most canning processes use batch or retort but larger production is achieved more economically with a continuous system. The Campden process which is a botulinum cook is the most effective.
Very high premium pet foods use single-serve pouches and trays with foil lids. many European pet foods have meaty chunks in a gravy and jelly. It has become one of the leading innovations of the business.
Semi-Moist Pet Foods
The intermediate mositure pet fods have a 25 to 35% moisture content. They use various water soluble solids such as sugars, salt, sorbates as preservatives and propylene glycol. All is sufficient to stabilize the pet food by controlling water availability and keep the product at ambient without the need for refrigeration.
This type of pet food is not as popular as it used to be and is being replaced by semi-dry foods where the moisture content is between 15 and 25%. This is a softer version of kibble.
Manufacture Of Dry Pet Food (Kibble)
Dry pet food is less than 12% moisture. It usually contains a wheat or corn starch, some fat which is commonly tallow or poultry fat, vegetable oils, a protein from legumes such as soy but increasingly pea or other cheap bean source, the alternative protein being meat, offal or fish meal.
The meat used is often waste material or by-products from butchering which are not suitable for human consumption. These include lungs, tripe, kidneys, tongue, beef lips etc. The poultry offal include feet, heads and viscera. Much of this waste meat is low in fat hence the need to coat it with lard or tallow. This addition can make up to 10 per cent of the total offering.
A number of bioactives are added for special health benefits including vitamins, amino acids, minerals and preservatives.
The process of manufacture of a dry pet food is very straightforward. Most pet foods are manufactured using extrusion cooking methods. Dyes are also added to make the meat more attractive.
All the ingredients are mixed together in a large hopper before passing through a single-screw or twin-screw extruder.
Post-coating of the food is often conducted to improve the palatability. The food is made appetising by spraying it with a fatty grease but it makes it difficult to package and handle.
The palatability of this type of pet food depends on spraying particular types of homogenized protein and fat mix onto the product. Another method of improving palatability is to add fat into the mix.
The Use Of Extrusion
Extrusion is a successful processing method for producing a wide variety of foodstuffs from various ingredients. Most breakfast cereals as are dry pet foods, are manufactured this way. Research on this subject has largely been limited to commercial investigations into the ideal processing conditions for these types of products.
Extrusion cooking is done using either single- or twin cooking extrusion. Extrusion involves an extrusion screw that rotates inside a tight fitting barrel of defined length and diameter. As the mixture moces along the barrel it is subjected to both thermal heating and mechanical/frictional forces. The whole mixture forms a plasticized mass that is forced through a die. On leaving the die, the release of pressure causes moisture to rapidly leave producing puffing and expansion.
The same chemical changes that take place in processing pet food are also to be found in human foods. Starch gelatinization is a critical phenomenon which needs as much care and understanding in whatever food is manufactured.
Fats have a profound impact on the quality of food, not just from a nutrient perspective but also on the manner of the processing itself. The type of fat and the way it is handled have considerable bearing on how the petfood will taste. One study at the Departments of Biological and Agricultural Engineering and Food Science and Human Nutrition in the University of Missouri-Columbia, Columbia (USA) found that poultry fat and beef tallow have very different impacts (Lin et al., 1997). In their study they looked at the production of a kibble and how fat type and processing factors affected the degree of starch gelatinization.
The fat content has the most profound effect on the way starch gels. Generally, increasing fat content from zero to 75g/kg and initial moisture levels rising from 160 to 200 g/kg reduces the degree of starch gelatinization. Beef tallow has a bigger impact than poultry fat on a weight basis.
Lin, S., Hsieh, F., & Huff, H. E. (1997). Effects of lipids and processing conditions on degree of starch gelatinization of extruded dry pet food. LWT-Food Science and Technology, 30(7), pp. 754-761 (Article).