The physical characteristics of a premix are crucial in ensuring flowability, mixability, and homogeneity of a blend, as separation of the components during transport and feed manufacture can be detrimental in ensuring a consistent ration of nutrients to an animal.

Hygroscopic ingredients, such as niacin or choline, can cause both physical and chemical issues within a premix in humid conditions. Weight increase and a visual score is given to determine how ingredients behave during manufacture and under different environmental conditions.

The difference between a kilogram of rocks and a kilogram of feathers – one takes up a large amount of space per unit of weight. Bulk density is determined for both individual ingredients to provide an estimate of a premix’s bulk density or done on the premix itself. Modifications of premix carriers can be done to increase or decrease bulk density, to better fit in a bag, or flow better through a feed mill.

Particle Size distribution - The ideal bell-shaped distribution of a premix can only be attained if a good quality carrier (wheat middlings or rice hulls) with a similar particle size distribution to the nutritive particles is used. Fine vitamin particles can segregate easily if the carrier has a large particle size (eg calcium carbonate).

Vitamins and minerals range in particle size, from large particles (e.g., Vitamin E) to small dense particles (e.g., minerals). It is important for all the components in a blend to remain suspended within the premix during transportation, mill or equipment vibration. Determining how a specific premix behaves under these conditions can be tested using a Vibratory trough, which simulates segregation cause by vibration and fall.