Food powders can be classified into different categories according to their handling properties. The
bulk properties of food powders are a function of physical and chemical properties of the material,
the geometry, size and surface characteristics of the individual particles, as well as the history of the
system as a whole. This chapter introduces some ways to evaluate food powder failure properties, such
as angle of wall friction, effective angle of internal friction, failure function, cohesion, flowability,
compressibility and other mechanical properties. These mechanical properties can be combined with
environmental conditions such as moisture, temperature, particle size and chemical composition in
order to condense physical and chemical issues related to the powder during manufacturing and
distribution. Shear testers are used for bi-dimensional stress quantification that leads to the calculation
of these properties. Other direct measurement methods for failure properties are also introduced.
Handling properties such as angle of repose, angle of slide, conveying angle and angle of spatula are
provided with some relevant reference methods, and new methods such as rapid methodologies are
utilized for evaluating drainage, flow or conveying capabilities. Powders are classified according to
handling in dispersion systems or according to their dynamic or static conditions during transport or
Bulk density and porosity are of fundamental practical use when doing quality control in the food
industry. These parameters can help to determine, for example, whether a raw material can be mixed
or a final product can be packed in a predetermined container. Bulk density is classified depending
on its measurement method. Particle size, voidage and other properties are studied with known
equations, including bulk density as a variable to see the influence of other conditions. Food powder
compressibility is useful to evaluate the extent of the intentional or unintentional compression that a
powder suffers during transport or production. Examples of compressibility values are shown, as well
as useful models are developed in order to explain compression mechanisms. Strength properties,
especially for brittle and fragile powders such as agglomerated coffee or milk, explain attrition
phenomena for these types of powders. Abrasion and friability illustrate how these degradating
physical processes occur.
The last section of this chapter reviews instant properties in relation to powder solubility in
water and rehydration properties. Different instant properties are defined, as well as standard and
non-standard methods for their evaluation.
3.1.1. Introduction
Powder flow is defined as the relative movement of a bulk of particles among neighboring parti-
cles or along the container wall surface (Peleg, 1977). The practical objective of powder flowability
investigations is to provide both qualitative and quantitative knowledge of powder behavior, which can
be used in equipment design and in equipment performance prediction (Sutton, 1976). The flow char-
acteristics of powders are of great importance in many handling and storage situations encountered