To process ground nuts, some initial precautions need to be taken during harvesting of the crop
The timing of the peanut harvest is critical since it can greatly affect the yields and nut quality. As harvest time approaches, the peanuts should be inspected every day or two to determine the best date for digging. While the type, variety and planting date may be used as rough guides for determine the harvesting date, the best way to judge the maturity of the plant is to examine the pod itself. The crop is ready to harvest if the majority of the kernels are fully developed and take on a mature colour. Harvesting consists of either digging or pulling up the plants manually or using mechanised means such as a digger or southern plough. After the groundnuts have been harvested, they are inverted and placed in windrows in the field. The groundnuts are left to dry for about two weeks. During this period, the moisture content of the pods is reduced to about 10 per cent. In humid areas, the pods are sometimes picked off first and dried on mats so that they can be stacked or covered in the event of rain.
The three main stages of oil-processing are:
(i) Pretreatment: namely, the stages prior to the extraction stage such as cleaning, crushing and scorching. (ii) Extraction: this stage involves the separation of the raw material into oil and residue (cake). (iii) Post extraction treatments: comprising the packaging of the oil and cake for marketing.
Improved power ghanis have an oil extraction efficiency which is fairly close to that of small-scale expellers, and often constitute a viable alternative to the latter, especially in rural areas.
Crushing can be done in a small powered hammer mill. These are available from equipment manufacturers in many developing countries. Capacity should be above 100 kg/hour, and reduction should ideally be to pieces less than 0.5 cm square.
It should be noted that pre-crushing is not traditionally used with ghani extraction.
Oil extraction by pressing --
double-ghani mill, powered off a single 3 hp motor can be used.Each ghani takes a charge of about 35 kg which is processed in approximately one hour by the rotary movement of the iron pestle in the bowl. Thus, such a unit may process up to 560 kg of seeds per day. The two ghanis may also be powered by separate engines. In this case, 2 hp motors are needed. The pestles in power ghanis rotate at approximately 10 to 12 revolutions per minute as compared to 3 to 5 revolutions for bullock-powered ghanis.
A large number of designs of powered ghanis have been developed and marketed in India.
For further details contact Appropriate Technology Development Association, P.O. Box 311, Ghandi Bhawan, Mahatma Ghandi Road, Lucknow-226001 (India). This institution may then provide names of ghani manufacturers and/or individuals willing to provide detailed drawings of ghanis for local manufacture.