Flowability, of food powders

Ehlermann, D.A.E. and Schubert, H. 1987. Compressibility characteristics of food powders Characterizing the flowability of food powders by compression tests. In Physical Properties of Foods—2 (R. Jowitt, F. Escher, M. Kent, B. McKenna, and M. Roques, eds). Cost 90bis Final Seminar Proceedings. ECSC, EEC, EAEC, Brussels and Luxembourg. 

Peleg, M. 1978. Flowability of food powders and methods for its evaluation. A review. J. Food Process. Eng. 1, 303-328. 

Compression and compaction parameters such as density, porosity, stress, and strain are introduced. Furthermore, other factors of importance in stress measurement of powder beds in different situations such as compression, tension, shearing, and impact are explained. The fluidity of food powders is a controversial topic in food powder characterization and of top relevance in the food industry. Concepts such as compressibility and other flowability indicators are important for understanding the effects of compression phenomena during storage, production, and handling. Food powder strength concepts such as hardness relate to other concepts like attrition, which are a common occurrence in compaction processes. 

Teunou, E., Fitzpatrick, J.J., and Synnot, E.C. 1999. Characterization of food powder flowability. 

The influence of key parameters, such as particle size and moisture content, in food powder development, manufacturing, and control has been widely studied. Other effects provided using cells with different geometries, mixtures of different size particles, or anticaking agents can also be found in various publications. The following sections summarize a literature review of historical contributions and new research on these effects and the use of compression properties for flowability characterization. 

Conversely, Ehlermann and Schubert (1987) sustained that compressibility results from materials of different composition cannot be compared and that flowability characterization through compressibility must be made specifically for each food variety. Moreover, confined uniaxial compression is a simple compression test that provides an approximate measure of the flowability of powders. Therefore, it is not suitable for silo design but may prove to be a convenient method for process control in any food laboratory (e.g., to evaluate particle cohesion). Table II offers a range value definition for flowability classification by comparing flow function (ratio between the maximum consolidation stress and unconfined yield stress) with compressibility. 

A very common undesirable aspect of compressibility is its negative influence on flowing capacity. Compression tests have been used widely in pharmaceutics, ceramics, metallurgy, civil engineering, and in the food powder field, as a simple and convenient technique to powder compressibility and flowability. 

Bulk characteristics, such as temperature, bulk density, and flowability, may be adjusted in a preparatory step to improve size enlargement. Prior to briquetting into ration-sized agglomerates, vegetables, food pulps, and fruit juices maybe frozen. Metal dusts and powders, as well as certain minerals, are often heated and briquetted hot to make use of their increased malleability at elevated temperatures. 

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