Fish Nutrition & Feed Technology

Unit 10 - Methods of feed formulation and manufacturing

10.5.2.Grinding

1. Hammermills
2. Attrition Mills
3. Roller Mills
4. Cutters
5. Screening

Grinding or particle-size reduction is a major function of feed manufacturing. Many feed mills pass all incoming ingredients through a grinder for several reasons:

• clumps and large fragments are reduced in size,
• some moisture is removed due to aeration, and
• additives such as antioxidants may be blended.

All of these improve the ease of handling ingredients and their storability.

There are other reasons for grinding and the associated sieving of ingredients in formula feeds before further processing. Small fish and fry require plankton-size feeds available in dry form as a meal or granule. Extremes in particle sizes are wasteful and often dangerous. Fry have been killed because of their inability to pass through the digestive system large pieces of connective tissue and bone present in dry animal byproducts, or hull fragments found in cottonseed meal and rice bran. On the other hand, dust or "fines" may become colloidal suspensions in water, so dilute that several mouthfuls carry little nutritive value.

The grinding of ingredients generally improves feed digestibility, acceptability, mixing properties, pelletability, and increases the bulk density of some ingredients. It is accomplished by many types of manual and mechanical operations involving impact, attrition, and cutting.