A questions OF FOOD

If you have any technical enquiries, please write to the Technical Enquiry Unit at IT. Enquiries of general will be published on this page in each issue of Food Chain.

Dear Sir/Madam

I read from Intermediate Technology News, September 1990 of a manual press for cooking oil being promoted in Malawi applicable for oil crops like groundnuts and sunflower. My Burmese friend, Arthur Mundt of Yezin, Myanmar, is looking for such a manually operated press for oil extraction and will be very interested to acquire a unit or build a prototype if they find the design suitable, especially for sesame seeds. YOU can send this information to me and I will add this to my other compilation of potential designs for my friend.

Sincerely

Eulito U Bautista, IRRI Agric Eng,

Manila, Philippines

We have been using the spindle press to process goundnuts in Malawi and a very similar design is in use in Zambia for sunflower; at present, we are encouraging the design in Zimbabwe for sunflower. One thing should be made clear at the outset, the oil press is only one part of a process. Use of the press directly, without conditioning the oilseeds beforehand will not produce much oil. For groundnuts, the process is briefly as follows:

1. Grading by hand, to remove possible aflatoxic nuts.

2. Size reduction, to reduce groundnuts to a flour. This step can be achieved by traditional hand pounding in a mortar and pestle. We have, however, developed a design of manual roller mill to reduce the laborious nature of this step.

3. Winnowing, to remove skins from groundnuts. Optional.

4. Moisturizing. With groundnuts, 10 per cent by weight of water is added and mixed thoroughly with groundnut flour.

5. Heating. Flour is heated to 90°C for 10-15 minutes and stirred continuously to prevent charring. The end point of heating is quite critical but can only really be judged by experience. Initially, the moisturized flour will clump or stick together, when compressed in a fist. As the heating is completed, the flour becomes a free flowing powder and will not stick together when compressed into a fist.

6. Pressing. The heated flour is placed in the cage and a sandwich built using the metal pressure plates, these assist oil extraction and the removal of the oil cake from the press. The spindle is then compressed slowly. Once oil flows pressure should cease until the flow stops, and then resumed. The end point is reached when no more pressure can be safely applied by four people - two on each arm of' the press - or practically when five screw threads remain above the top frame of the press.

After pressing, the spindle is raised and the cage now containing the oilcake, is raised on the brackets on the press frame. The spiedle is again lowered, and the cake and plate sandwich expelled from the cage. The cakes can be separated into discs and are an important byproduct of the process and can be used directly to improve human nutrition (the protein content with groundnut cake is about 40 per cent), or the cake may be used for animal feed.

Finally, the oil is left to stand overnight for removal of gross solids, filtered and finally boiled, before sale. No refining process is involved.

The process is thus a batch process, with a l0kg charge of oilseed per batch. With a practiced team, 10 batches per day is achievable. The yield per batch will depend upon the seed type and oil content, but with groundnuts of 45-48% oil content the yield is 3.0-3.5 litres per batch.

With regard to using the process for sesame, I see no reason why the process could not be used. Tour friend would have to experiment as it may be possible that the diameter of the holes in the cage would have to be reduced, due to the small size of the seed.

With sesame the process may be even more straightforward, as it may prove unnecessary for processing steps I to 3.

I hope the above proves useful, if you or your friend should decide to build a press, or if you should require any further information, please get in touch.