Microwave processing of capsule-less powdered beverages

Abstract

Microwave rapid and selective heating is successfully applied to produce freestanding capsule-less doses of powdered beans or leaves for hot beverages preparation. 1 or 3-person doses, suitable for use in conventional hot beverage preparation machines are obtained in less than 5 seconds, without any additives except for water. Microwaves at 2.45 GHz are applied to allow shape retention and surface hardening of the pressed powders, thanks to the rapid steam generation. Load is contained inside a PTFE-lined applicator presenting micro-holes on two sides, to control vapor outlet. The use of rapidly generated steam, preferentially on the outer layers of the load, leads to weak bonding of the powders, without affecting the final taste of the brewed beverage. Modeling of the temperature- and moisture-dependent dielectric properties is used to optimize the applicator geometry, so that the outer layers of the pressed powders are preferentially heated, thus creating a rigid “shell” hosting the remaining pressed powders.