2.1.2 Oil seeds

(see Flowsheet 2)

Flowsheet 2 Traditional (wet) Process for Processing Oil seeds (General Flowsheet)

1. With groundnuts, palm kernels and often with shea nuts.

2. By pounding, crushing between stones or a stone and an iron bar or by the service mill; fresh coconut is grated.

3. Groundnut paste is treated by stirring and addition of some water (12 %). Crushed palm kernels are cooked in excess water. Shea nut paste is treated by beating in air and washing of the cream or cooking in excess water.

4. Tunkusa and kuli-kuli for human consumption from groundnuts; animal feed from palm kernels and coconuts.

Groundnuts

Groundnuts are almost exclusively processed in combination with the utilization of the residue for human consumption. In fact often the by-product, a kind of a snack, has to be understood to be the main product and the manufacturing of the groundnut oil only as part of the process.

In Ghana the following process was observed:

- decorticated groundnuts are roasted, treated by a rubbing action and winnowed to remove the pellicles
- the nuts are crushed between stones, several times to obtain a fine paste
- this paste is stirred vigorously, while gradually adding some hot and/or cold water (about 10 % w/w)
- when the oil appears it is skimmed off and the mass formed into large balls and some more oil is pressed out by hand; the balls are called: tunkusa
- the tunkusa is subsequently processed into kuli-kuli, a ring or ball-shaped snack, prepared by frying products moulded out of tunkusa in groundnut oil. It can also be used as the main ingredient for “groundnut soup".

For Burkina Faso, a similar process has been described.

A typical example has shown a recovery of 0.5 kg oil and 3.5 kg kuli-kuli (out of 3.8 kg tunkusa) from 4.0 kg of groundnuts; the production of the oil and tunkusa took 5 man working hours.

Palm kernel

After cracking the palmnuts, the palm kernels can be separated out. Traditionally they are processed into an oil after roasting. The roasting makes the palm kernels brittle and more easy to crush by pounding. However, the quality of the oil deteriorates because of the temperature and the oil becomes dark coloured. After roasting the kernels are pounded. Then the pounded mass is mixed into excess water and boiled for hours, during which the oil is skimmed off. Finally the oil is dried by heating. 18 kg of palm kernels give I gallon or 4 kg of oil in about 12 man working hours.

Coconut

The basic way to process fresh coconut is to cut the coconut lengthwise in half and to remove the white kernel or so-called 'meat'. The meat is first grated on a grating surface by hand then mixed with water and pressed out by hand or foot. This procedure is repeated several times. The coconut milk obtained is left to stand for a few hours to permit the separation into a supernating oil-containing cream and water. Subsequently the cream is collected and transferred into a cooking pot and heated under continuous stirring to dry the oil by boiling. The protein in the cream coagulates and dries. The oil is filtered. The residue can be eaten as a snack.

Shea nut

Also shea nuts are processed following a wet process. This process has been studied in Mali and includes:

- drying and roasting of the nuts - decorticating of the nuts
- pounding of the shelled nuts into a liquid mass, that contains particles smaller than about 3 mm
- crushing of the mass into a very fine paste between stones or a stone and a metal bar
- in some areas the brown paste obtained is mixed into water, and air is brought in by beating, a cream appears; this cream is washed several times to remove all brown particles and transferred into a cooking pot; the cream is heated until the oil is collected at the top; the oil is skimmed off
- in other areas or later in the year the brown paste is mixed into boiling water and boiled for an hour, after which the oil is skimmed off; more water is added and boiling continued; finally, a second layer of oil is skimmed off
- by the next day the oil has hardened into a fat, and can be packed in leaves.

The time required for processing (grinding and oil extraction) of 12 kg shea kernels was found to be at least 18 man working hours, of which 14 hours were required for grinding. Generally, however, much more time is needed. Oil recoveries depend on the quality of the nuts and the skills of the women and can range from 20 % to more than 40 % on kernel weight. Normal yields have been reported to be between 20 and 30 %. In South Mali, recovery rates of 34 to 41 % have been reported recently.

Possibilities for improvement

Traditional methods make use of readily available utensils as a pounding mortar, crushing stones, calabashes and cooking pots. As they all apply water to assist the separation of the oil, these methods have in common that crushing of the seed into a very fine paste is essential. This stage is the most time consuming and exhausting one. This drawback of traditional methods can only be overcome by crushing using mechanical means. Such means, as motorized mills, require considerable investment and are only feasible at the village level. In fact they are already available in many villages in the form of so-called “service mills".

The only way to avoid the use of a motorized mill is to change to a complete dry process using a hand press. During this process the seed is treated before pressing with care, by crushing into flakes, moistening and heating, in order to make the oil available so that it can easily be extracted by pressing.

The equipment to be used is unsophisticated and sturdy. However, investments required are only feasible at the village level. The process will be treated in detail under 2.2.2.