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close this bookFood, Nutrition and Agriculture - 11- Edible Fats and Oils (FAO - FPND - FAO, 1994)
close this folderGhani: A traditional method of oil processing in India
View the document(introduction...)
View the documentTraditional ghani technology
View the documentCrushing oilseeds
View the documentOil yield
View the documentRecent evolution of oil processing
View the documentAdvantages and disadvantages of ghani crushing
View the documentBibliography

Traditional ghani technology

The oilseeds and subsequently the expressed oil are held in a scooped circular pit in the exact centre of a circular mortar made of stone or wood. In it works a stout, upright pestle which descends from a top curved or angled piece, in which the pestle rests in a scooped-out hollow that permits the pestle to rotate, eased by some soapy or oily lubricant. Today the single angled piece takes the form of two shorter pieces pinioned or chained together. The bottom of the lower angled piece is attached to a load-beam; one end of the load-beam rides around the outside of the barrel, while the other is yoked to the animal. The load-beam is weighted down with either heavy stones or even the seated operator. As the animal moves in a circular ambit, the pestle rotates, exerting lateral pressure on the upper chest of the pit, first pulverizing the oilseed and then crushing out its oil.

Within India there are regional variations in ghani design (Patel, 1943;Chaudhuri and Selvaraj, 1985), which probably arose from the nature of the oilseeds that were regionally available for crushing. The large granite ghanis of southern India have a capacity of 35 to 40 kg, requiring two animals yoked side by side and two operators, one for the animals and the other near the mortar. The load-beam is very long and curved and rides on a strong outer groove on the mortar. These ghanis have a life of four to five years, after which the pit is too worn to be useful. The wooden ghani of western India has a capacity of 8 to 15 kg, has an oil outlet at the base of the pit (which is kept plugged during crushing) and frequently has the operator seated on the load-beam. The Bengal ghani has a small capacity of only 5 to 10 kg per charge and is usually used to crush a mixture of rape and mustard seeds to yield a bouquet of flavours. The pit is small and the pestle is tall and has a stout base. The operation is prolonged so as to permit slow enzymatic liberation of several pungent alkyl isothiocyanates from the precursor glucosinolates in the prevailing warm, moist conditions. Punjab ghanis are of similarly small capacity but generally carry a short pestle.

Traditional Indian ghanis for crushing oilseeds - Ghanis indiens traditionnels pour le pressage des graines olineuses - Ghanis indios tradicionales para la molturacie semillas oleaginosas

For the mortar, the trunks of hard woods such as the tamarind tree (Tamarindus indica), neem (Azadirachta indica), jack (Artocarpus heterophyllus), baheda (Terminalia bellirica), shirish (Albizia lebbeck) and sal (Shorea robusta) have been utilized regionally, all these being very large trees (Patel, 1943). Pit designs also vary with region, and could even take the form of a wooden sleeve that sits snugly in the cavity and is less expensive to replace (Patel, 1958). Even wooden strips laid radially in the pit cavity are in use. The pestle is generally made of baheda, shirish or babul (Acacia nilotica) wood, with a bulbous tip sometimes clad with lengthwise metal strips. The shape and design of the pestle end must match that of the pit to avoid excessive dead space (Nag, 1982). The curved or angled piece was once fashioned out of a single large piece of wood; a shortage of these has led to the use of two pieces, the top one angled or curved and the bottom one straight; these are tied, chained or pinioned together for easy detachment when the pestle has to be removed. The strong load-beam has to be designed so that lateral pressure on the animal does not force it to lean from a comfortable upright stance during ambulation. Trained male animals, cattle or buffalo, are generally used, usually blindfolded to avoid dizziness and distraction; however, on small ghanis in certain areas even human labour, both of men and women, is employed (Achaya, 1993).