Production of quality dog food kibble is no easy feat. Of course, we’ve been producing this type of food for nearly 70 years and it makes up nearly 70% of the market. But we still have much to learn about pulling all the key elements together and producing a consistent-quality product, and when you add the scrutiny that pet food is now under from consumers, regulators, and supply chain challenges it can get complicated pretty quickly.

The beginning: ingredient considerations

It all starts with consistent, quality ingredients. Many of the pet food battles today are being fought along the ingredient choice line. For the producer, one type of ingredient processes quite differently from another, and adding meats to the equation complicates things even further. While the process of pushing raw ingredients through an dog food machine sounds straightforward, the composition of those ingredients can have a profound effect on what comes out the other end:

The grind size of the starch sources and the consistency of the mix: Very coarse material and we end up with less expansion and more fines; too fine and it affects the dynamics of moisture absorption and changes the way in which one has to run the preconditioner and extruder.

The uniformity of the mix: An inconsistent mix will lead to fluctuations in the fortification and surging in the process.

Preconditioning to convert starches and aid safety

Once the mixed ground ingredients are delivered to the preconditioner, they should be complete blends with the exception of the liquid topical ingredients. The preconditioner is responsible for the initial process — adding steam and moisture and more mixing. This is where the cooking of the starches (gelatinization) begins. It adds residence time and heat to accelerate the reaction and starts the unpacking of the starch granules.

This is where some add meat slurries and fats. They should be added toward the middle to end of the conditioning steps lest we coat the starch granules and diminish the penetration of water and heat and delay gelatinization. Finally, some companies use the preconditioner for product pasteurization — the “kill step” for pathogens. The temperature at the end of the preconditioner should reach approximately 80°C for 30 seconds to assure a near complete knock down of organisms to provide compliance with the Food Safety Modernization Act (FSMA).

Extruding the results

Once the preconditioning process is complete the mash drops into the extruder. The extruder is a screw or auger within a barrel. The physics are such that we increase the flights per turn in order to compress the mash as it moves to the end of the barrel. This dog food production line process adds friction (mechanical energy) and is commonly described as “shear.” This shear increases the amount of energy that is transferred to the product.

At the end of the barrel the bulk solid (granular) flour or mash is converted into a molten mass (often called the “melt”), and the remainder of the cooking to gelatinize the starch occurs. The melt escapes from a small opening or die hole and exits the machine; as it does water droplets mixed into the melt begin to vaporize and then expand creating spaces trapped within the molten starch. The product expands and creates the kibble structure.

Drying the extruded kibbles

Today, much of this conveyance is done by dense phase pneumatic systems that reduce the deformation and breakage of traditional belt and screw conveyors. Modern drying equipment involves a massive volume of hot, dry air in a continuous process. At the end of the dryer kibbles may have been in residence for upwards of 25–30 minutes and may be heated to a temperature exceeding 250°F (121°C). That is much too hot to package as any latent moisture may still be active in the product and could lead to mold growth in the container. So, it passes to the “cooler” — a last leg of the drying process in which ambient air is circulated around the product in order to bring the temperature down and remove any remaining surface moisture.