Experimental and numerical investigation into the destemming of grapes

[摘要] ENGLISH ABSTRACT: The removal of grape berries from the stems is an important step in the winemaking process. Various problems are experienced using the destemmingmachines currently available, where the berries are mechanically removed andseparated from the stems by a rotating beater shaft and drum. Not all berries areremoved from the stems and broken stems can end up with the removed berrieswhich can result in unwanted characters and flavours in the wine. Thedevelopment of these machines is currently limited to experimental tests.In this study, the destemming process was investigated experimentally. Theability of the Discrete Element Method (DEM) to simulate this process was alsoinvestigated. A range of experiments was designed to obtain the materialproperties of the grapes. These experiments included the measurement of thestem stiffness and break strength, the berry stiffness, and the force needed toremove a berry from the stem.Experiments were conducted to gain further insight into the destemming process.Firstly, a simplified destemming machine with only a beater shaft and a singlegrape bunch was built. The influence of the bunch size and the speed of thebeater shaft on the number of berries removed from the stems were investigated.Secondly, field tests on a commercial destemming machine were conducted andthe performance of the machine was measured.A DEM model of both the simplified and the commercial destemming machinewere built. Commercial DEM software was used with linear contact and bondmodels. The stems were built from spherical particles bonded together and asingle spherical particle was used to represent each berry. The measuredstiffnesses and break strengths were used to set the particle and bondproperties. Modelling the simplified destemming machine, it was found that theDEM model could accurately predict the effect of the bunch size and the speed ofthe beater shaft on the number of berries removed from the stems. The model ofthe commercial destemming machine could accurately predict the machine'sperformance in terms of the number of berries removed as well as the number ofbroken stems.

[发布机构] Stellenbosch University