(491e) Quantifying the Extent and Rate of Caking in Food Powders

“Caking” is the phenomenon where materials gain strength during storage due to changes in the particle/particle interactions. A significant number of materials, including raw feeds, additives and process intermediates, from a wide range of industries are susceptible to these changes. Following storage, previously free-flowing and easily processable powders can have limited ability to pass uninterrupted through their process and this can have a detrimental impact on product quality. Therefore, the ability to quantify the extent, strength and rate at which a powder cakes is vital to process operators and designers. This presentation demonstrates how the caking of food powders can be quantified using powder flow characterization techniques.

Caking can occur via a number of different mechanisms: mechanical, thermal, environmental and/or chemical. A combination of mechanisms is discussed in this study, where the high levels of fats and sugars within food powders can also intensify the strength and rate of caking. Some caking mechanisms can be controlled by managing environmental conditions, however this can be impractical and uneconomical. Accurately quantifying unacceptable characteristics and the stimuli that contribute towards caking for particular powders is therefore highly advantageous.

A range of food powders were evaluated to investigate the effect of extended storage time and environmental conditions on their flow properties. Samples were placed into 25 ml cylindrical vessels and initially conditioned using an FT4 Powder Rheometer® (Freeman Technology Ltd, UK). Conditioning was completed by passing a bespoke, twisted blade through the powder along a prescribed helical pathway. This promoted the formation of a uniform powder bed with a repeatable stress state within the sample. The test samples were then stored in an environment at controlled humidity and temperature levels for predetermined time periods. Stored samples were analyzed using the same bespoke blade and test parameters to measure the powder’s resistance to motion and quantify the relative change in flow properties as a result of caking.

Analysis of the powder’s resistance to motion with respect to blade position provides strong evidence of localized caking within some materials. At elevated humidity levels, some powders gained strength at the powder-air interface, forming a “crust”. It was possible to easily evaluate both the strength and depth of the crust and improve understanding of moisture migration through the powder bed.

This study demonstrates that caking is a complex phenomenon and that powder flow characterization is a relevant technique to quantify the progression of caking as a function of time, relative humidity and temperature. In turn, this characterization can assist with adapting the process environment or parameters to limit caking and retain optimal processability.