Performance evaluation of a bolt type pistachio hulling machine

Abstract

Most of the pistachio production is hulled by bolt type hulling machine in Iran which is the first world producer of pistachio, the only commercial type of hulling machine manufactured in the country. This study was conducted to evaluate the performance of this machine. The selected machine hulling capacity was 6 tons per hour. The selected pistachio variety was Ohadi, one of the important Iranian pistachios. The performance was measured 3 times at equal intervals of one week for 3 subsequent weeks during the harvesting season. A small box with the volume of 2200 cm3 holding about 1000 pistachios was used to collect samples from each machine outlet;the numbers of hulled, unprocessed and broken pistachios were counted. These three parameters were used to evaluate the machine performance. Higher number of hulled pistachios and lower number of unprocessed and broken pistachios indicate better machine performance. The statistical analysis of the data indicated that there is no significant difference between the four machines performance. The experiments also showed that there is no significant difference among the percentage of pistachios hulled at the beginning of the season and those hulled at the end of the season (at 3 subsequent weeks). The best machine adjustment, for minimum pistachio breakage which was achieved at a clearance of about 5 mm between the rotating drum and sharp hulling blade. At this clearance the machine hulled 73.8 percent of pistachios, 25.5 percent remained unprocessed which needed further hulling operations and 0.7 percent of the pistachios were broken.