Influence of the Forming Die Design on Processing and Physical Properties of Gluten-Free Crisps

The aim of the research was to evaluate the influence of the forming die openings shape on processing parameters of the extrusion-cooking process and on the selected properties of gluten-free crisps. The experiment used blends of corn grits, unroasted buckwheat, rice, and dried blackberries. The extrusion process of gluten-free crisps was carried out via a prototype EXP-45-32 single-screw extruder with L/D=16. During the tests, 5 different forming dies were assessed: 2 openings with a diameter of 2 mm each, 1 round opening with a diameter of 3 mm, 1 cross-shaped opening, a star and a heart. During the tests, the processing efficiency and energy consumption of the extrusion process were tested, and the expansion index, bulk density and hardness of the crisps were investigated. The research demonstrated that the forming die shape affects the efficiency and energy consumption of the extrusion-cooking process of crisps. The lowest efficiency was found if a heart-shaped die was used, and the highest efficiency was determined in the case of a star-shape die. Moreover, the highest specific energy consumption was noted when using a star-shaped die during crisps extrusion. Crisps obtained using dies with larger diameters were characterized by a lower expansion index. The complicated shape of the die opening resulted in less expansion of the obtained crisps. The highest bulk density and hardness were found in the case of crisps obtained on a star-shaped forming die.