Comparison of impact hulling of almonds using 3 impellor geometries

Abstract. Almonds are a major horticultural crop grown primarily in California, Australia and Spain. Almonds come in many varieties which have different shell types (soft, semi-hard and hard), kernel shapes and flavors. In California and Australia most varieties are soft shelled. Almond growers allow the fruit to dry on the tree, mechanically shake them to the ground and after drying to a kernel moisture content less than 6% are collected for processing. The first step in processing is the removal of the hulls. As almonds are more valuable to Australian producers as an inshell product, processors desire to only remove the hull and leave the kernel in its shell. Hence, this work is about maximizing the creation of inshell almonds without creating too many loose kernel.

This research shows that impact threshing of Nonpareil, Carmel and Marcona varieties is a viable process to achieve a high proportion of inshell almonds. The best hulling performance was achieved using early harvested fruit. Tests were undertaken using three different geometries of impellor blades. High speed video showed the different blade geometries created different fruit impact angles with the outer wall of the impact thresher.

For the soft shelled Nonpareil variety of almonds the impellor with radial blades created the most inshell with least creation of loose kernel. For the soft shelled Carmel variety the ultra backward blade with 60° backward facing blades performed the best. The work also highlighted that several lower energy impacts was preferred over one higher energy impact.