Rehydrating Food Powders and Avoiding Lumps: Effect of Powder Properties and Liquid Flow

Abstract

Poor dispersion of beverages from dehydrated powders is a defect that obstructs the development of novel dehydrated food powders. We investigate how the physico-chemical properties of the powder grains affect the dispersion process. We used insoluble and non-cohesive grains to form islands of powders at a static water surface. Liquid “wicking” can avoid the formation of lumps, lead to complete sinking of powder grains when the grain contact angle is below a critical value in the range 51°-77°. The effect of grain size on powder sinking, or on the depth of island formed, was experimentally studied to understand the impact of particle size enlargement on powder dispersion. The interplay of grain contact angle and size was also quantitatively demonstrated. We also report the conditions leading to the detachment of a powder island from the interface, forming a powder lump that is wet outside and dry inside. Importantly, introducing flow in the liquid by agitation does not necessarily improve the dispersion process.