Extruders for Feed Production
Extruders are the machinery used to produce extruded petfood, (floating) extruded aquatic feeds and extruded animal feeds.
The extrusion cooking process, because it causes a high level of gelatinisation of starches, results in feeds with good water stability. It can produce 'expanded' floating feeds as well as sinking pellets. The process also improves the digestibility of the product. However, extrusion cookers are usually very large and expensive to purchase and operate.
Feeds which have ingredients such as soybean meal and cereal grains can be made more digestable, and the nutrients are therefore more available. Floating feeds are made using extruders along with highly water-stable sinking feeds which can be made with extruders as well. In some cases, extruders are used just to prepare feed materials, such as dry extrusion of soybeans.
Basically, an extruder is a long barrel with a screw auger inside which is specially designed to subject feed mixtures to high heat and steam pressure. When feed exits the die at the end of the barrel, trapped steam blows off rapidly, the soft warm pellets expand, and a low density floating pellet is produced. Extruders are very versatile, and can make feeds with many different characteristics. The main problem with extruders is that they are expensive to buy and maintain, and the feed manufacturers pass this cost on to feed buyers.
Another type of feed which can be made on extruders are soft-dry feeds. This type of feeds are usually high in moisture (12-15%) and fat (15%). They usually contain a number of preservative agents to prevent spoilage. Soft-dry feeds can be used for fish that prefer to eat soft feeds, yet they do not need refrigeration like moist feeds.
A more in depth guide into extrusion and the extruder machinery can be seen in our articles section, in the following article: Extrusion Equipment Design And Selection