The effect of mechanical dehuskers on the quality of macadamia kernels when dehusking macadamia fruit at differing harvest moisture contents

Abstract

Dehusking to remove the fibrous husk of the macadamia fruit following abscission is an essential first step in postharvest handling of macadamia nuts. Commercial dehusking uses machines, causing trauma for nuts. Mechanical dehusking of macadamia fruit at “field” (mean harvest) moisture content causes shoulder damage but the effect on kernel quality of dehusking fruit that has dried while on the ground between harvest rounds to “low harvest” moisture content is not known. We dehusked macadamia fruit by hand and with two mechanical dehuskers at field moisture content (23%) and at low harvest moisture content (10–12%) after ambient drying for three weeks. After-roast-darkening (dark, reject kernels), shoulder damage and weight of pieces increased while whole kernel was reduced when dehusking at low harvest moisture content compared with dehusking at field moisture content. There were only minor differences between mechanical dehuskers for kernel damage and no difference between dehuskers for dark roasted kernel. Kernel quality of macadamia is more affected by slow, ambient drying than the type of dehusker used. Improving harvest management by reducing time between harvest rounds is more important to macadamia kernel quality than the type of dehusker used.