Screw press for cocoa butter extraction

Abstract

Cocoa butter is a natural fat extracted from cocoa beans. It is one of the main components of chocolate and is known for its unique creamy texture and flavour. To obtain cocoa butter, cocoa pods are first harvested from the cocoa tree and then cocoa beans are separated, fermented and dried. Afterward, the beans are roasted, which helps the development of their characteristic flavour. The roasted beans are then cracked using cocoa bean sheller and the cocoa nibs are separated from the cocoa shell by using winnowing machine. The nibs are then processed to separate the cocoa solids from cocoa butter. Most common method used for the cocoa butter extraction is hydraulic press, which is suitable for large scale cocoa processing. Extraction of cocoa butter is the main problem encountered in the small scale processing of cocoa beans. Hence this study is proposed to develop a suitable equipment system for small scale cocoa processing of cocoa beans. The study mainly concentrated on the development of a screw press type extraction unit for the separation of cocoa butter from cocoa nibs. The developed cocoa butter extractor consists of feed hopper, screw shaft, barrel/expelling chamber, control unit, oil outlet and cake outlet. The extraction of cocoa butter from cocoa nibs is performed by the combined action of temperature and pressure generated inside the barrel. As the material moves, the increasing screw diameter towards the outlet and decreasing volume between barrel and screw result in increased pressure within the press chamber, which ultimately separate the cocoa butter from cocoa nibs. In this study, three different process parameters with three levels were selected for the extraction of cocoa butter viz. barrel temperature (80, 100 and120°C), screw speed (50, 70 and 90rpm) and feed rate (2,3 and 4kg/hr) were optimised using Box-Behnken technique combined with response surface methodology. The optimized process parameters obtained for cocoa butter extraction were barrel temperature (100°C), screw speed (50rpm) and feed rate (4kg/hr). A maximum yield of 40 per cent of cocoa butter could be extracted at optimum condition. Characteristic study of cocoa butter and cocoa powder were carried out to obtain the quality as well as the proximate composition. The shelf life study of cocoa butter was done in polyethylene pouch of 80 micron thickness for a period of 3 months. Various quality parameters of stored butter were determined at regular interval of 30 days for 3 months. The cocoa butter quality parameters viz., iodine number, moisture content, peroxide value, free fatty acid (FFA) and water activity were within the allowable limits even after 3 months of storage. The total production cost of 1kg of cocoa butter was found to be Rs. 788. The developed cocoa butter extractor is economically feasible and commercially exploitable.