Issue 11 - June July 1999
From the Small Farm Resource page on the net
The extraction of oil from an oil bearing commodity involves some or all of the following steps, depending on the particular commodity to be processed, the scale of operation and the technical options available to the processor.
The first stage of the process sometimes requires the separation of the oil bearing part of the plant be it a nut, fruit or seed. The process is generally referred to as decortication or dehulling. Seeds with thin testa similar to rapeseed or sesame seed can be processed without decortication.
In most cases the oil bearing material is then broken into smaller pieces by pounding in a pestle and mortar or by manual or motorised grinding. When motorised oil expellers are used the decorticated or undecorticated material can often be fed directly to the expeller.
The next step involves heating the oil bearing material, sometimes with the addition of a little water to assist in the rupture of oil bearing cells and in the liberation of oil. At small scale this is carried out in a pan over a fire but mechanised heaters or kettles are available and used in commercial plants small scale heater-Cecoco.
Figure 1 - Small Scale Heater (scorcher) Cecoco
The oil bearing material is now ready for oil extraction. Five basic technical options exist; hot water floatation, ghanis, manual presses, powered expellers and solvent extraction.
1.Hot water floatation is probably the simplest method and is still used in many rural areas. The ground material is placed in boiling water and simmered for several hours. On removing from the fire and cooling the oil floats to the surface and is skimmed off. In general the oil is then heated in a shallow pan to drive off the last traces of water. This improve" the keeping quality of the oil as water has a catalytic role in the development of rancidity in oils. The extraction efficiency is generally low, and problems often occur with the formation of oil-water emulsions which makes the final separation difficult. In some cases salt is used to break such emulsions.
2.In many countries a large rotating pestle and mortar system known as a ghani is used for oil extraction. Ghanis are powered by animals or motors (power-ghanis) although sometimes human power is used. The mortar is firmly fixed in the ground and as the pestle rotates oil is released by friction and pressure and runs out of a small aperture at the base of the mortar. A typical one bullock ghani can process 40kg of material/day. In the case of power-ghanis either the pestle or mortar is fixed, the other rotating. Power ghanis usually are operated in pairs and have a typical capacity of 100 kg/day. The extraction efficiency is generally greater than animal units.
3.Other traditional methods are still used to extract oil from oil bearing materials. Such systems include the use of heavy stones, wedges, levers and twisted ropes to apply pressure to the material and so squeeze out oil. They are inefficient, of low capacity and labour intensive.
Traditional presses are now increasingly being replaced by better engineered, more efficient mechanical presses. Many different types of mechanical press are in use but they fall into two basic types, plate presses and ram presses. In the first type a plate or piston is forced into a perforated cylinder containing the oil bearing material by means of a worm. In some cases hydraulic jacks have been used, care is needed to make sure there is no leakage of hydraulic fluid that might contaminate the edible oil. In a ram press a piston forces the oilseed forward in a perforated cage fitted with an adjustable choke at the outlet, which controls the pressure. Ram presses provide a greater shearing action than simple screw presses and have been found to be considerably more efficient for some raw materials. It is important that when selecting a particular type of press its suitability for the raw material to be processed is determined.
FEATURE: Davidson Plum.
The Value Adders: Greg Trevena and Fudge A'fare
|Power Ghani||Plate Press|
|Mini 40||Traditional Animal Powered Ghani|
To obtain greater throughputs and extraction efficiencies it becomes necessary to use powered devices and the oil expeller is the most common of these. A whole range of expellers are available with capacities ranging from a few kg/hr up to tons/hr. They all work on the same basic principle. The raw material, which may have been previously heated to aid in the release of oil, is fed continuously to the expeller where it is fed by the wormshaft into a horizontal cylinder. A controllable pressure is built up in the cylinder by means of an adjustable choke at the cylinder exit. The internal pressure ruptures oil cells in the material and oil flows out through perforations in the cylinder cage. Some care has to be taken when selecting an expeller for a particular commodity. Many have been designed for particular applications, in terms of internal pressure, amount of shearing action etc. Certain types tend to be more adjustable and hence less product specific than others.
Small scale expellers c 40 kg/hr
None of the above extraction systems are able to remove all of the oil from a material. In most small scale rural situations this is of little or no importance as the cake, that remains after the oil has been removed, finds uses in local dishes, in the manufacture of secondary products or for animal feed. Some raw materials however do not release oil by simple expelling; the most notable being rice bran. In order to remove oil from commodities that do not respond to expelling or to extract the final traces of oil after expelling it is necessary to use solvent extraction. Solvent extraction is a high technology process that has to be carried out at comparatively large scale. Capital costs are high. Essentially the process is one of continuous counter-current extraction with the raw material flowing in one direction against a solvent; usually hexane. After oil extraction the solvent passes to a recovery plant where the solvent is stripped off under vacuum. The crude oil then passes on for refining. Due to the large scale involved it would seem unlikely that solvent extraction would find much application in minor oil product processing.
Griffith University Hosts a Great Day -
Five Speakers, an Association Formed and Lemon Myrtle Shortbread for Afternoon Tea
There was a packed audience, an intensive line-up of speakers and far too much food at the bushfoods conference held at Griffith University (Brisbane) August 21st.
Griffith University (Nathan Campus) kindly laid out the venue for this one day event and opened the proceedings with a brief but tantalising presentation of the work they are undertaking in micro and clonal propagation of selected bushfood species (see article page 14).
Nerandra Nand, a postgraduate student working under the auspices of Dr Rod Drew, brought out his `babies' - Davidson plum in their jelly medium. Nerandra gave an enlightening talk on the background and processes of micropropagation and clonal propagation - not to be confused with genetic engineering!
Drs Merv and Elwyn Hegarty joined forces to discuss the research they are undertaking into the constituents of bushfoods and Joan and Alan Cribb gave a fascinating two-handed talk on bushfoods - and native seaweed!
Dr Rob Fletcher had the audience by turns thoughtful and rolling in the aisles with his no-nonesense presentation on new crops and I attempted to keep an over-fed and rather fatigued audience inspired with an overview of the industry.
The open invitation for participants to bring their plants, products or promotional material was taken up by many and the special display area was crammed with books, food, posters, (free) rainforest fruit drink and trays of all-too-alluring bushfood plants. I went to the conference with 12 boxes of goods and came back with 14!
Morning and afternoon tea and lunch were all based on bushfoods - though finding fresh fruit proved a challenge (see menu opposite).
In between the talking, eating and networking, the Queensland Bushfood Association was formed and, I hope, some contacts made which will prove fruitful in the years to come.
My personal thanks to Dr Janet Gorst who leapt in with enthusiasm and time she probably couldn't spare to make the day work.
To Nerandra Nand, Dr Rod Drew, Dr Rob Fletcher, Sarah, Alan and Joan Cribb, Merv & Elwyn Hegarty and that nice man who helped me carry in my boxes - thank you. Let's do it again!
Response to the day was well above expectations, with close to 95 people wanting to book into a lecture theatre with seating for 60.
John King, Nerandra Nand, Merv & Elwyn Hegarty and the editor.
Joan and Alan Cribb, the editor and Dr Janet Gorst of Griffith Uni
The Queensland Bushfood Association:
Ph: 07 5494 3812 or
07 3284 2202
Queensland Bushfood Conference: the speakers and the food:
Pumpkin scones with a variety of bushfood jams
Aniseed myrtle bisquits
Macadamia cream scrolls
Lemon myrtle tea
Rainforest fruit drink
Bush tomato and native pepper sausage rolls
Warrigal green and bush tomato quiche
Filo pastry with fetta, Warrigal greens, Macadamia and a touch of Lemon myrtle
A variety of wholemeal breads (Wattle, Aniseed myrtle and Bush tomato)
Fresh Lilly pilly fruit (Syzygium australe)
Lemon myrtle cream shortbread
Dr Rod Drew opened the conference and welcomed guests
Nerandra Nand gave a plain-English insight into micorpropagation and cloning.
AB & AW Cribb: well known authors of the one of the most definitive bushfood books ever written - 'Wild Food of Australia', the Cribbs gave a delightful overview of bushfood species - concentrating on native seaweeds!
Dr Rob Fletcher: Lecturer in Crop Improvement at the University of Queensland, Gatton College. Rob is a Principal Investigator in New Crops. He is also the publisher of the Australian New Crops Newsletter and the Directory of Australian New Crops Workers. He also compiled and published the First Edition of the New Crops DOOR Marketing Information Booklet.
Drs Merv and Elwyn Hegarty: Dr Merv Hegarty AM (Hon Research Fellow, CSIRO Division of Tropical Ag) and Dr Elwyn Hegarty, are principals of Plantchem Pty Ltd, Brisbane. They provide information on sources, processing, storage and any potential toxicity of plants used (or considered for use) in various commercial products. With Prof. Wills of Newcastle, they are preparing a RIRDC and industry-funded report on safety issues for the bushfood industry. This will be completed this year.
Sammy Ringer: Editor of Australian Bushfoods Magazine - the industry and the future.
A professional nursery growing exclusively east coast bushfood plants
Northern Rivers Bushtucker Foods announces increasing availability of plantation tested rainforest bushfood trees for commercial growers.
The nursery is also linked to a consulting service for farm design, planning, species selection, marketing surveys and planting assistance.
Please ask for our species list. No hype, promises or
promotion, just sound trees and experienced advice.
Seedlings in trays: .25c. Tubes: $1.00
Advanced plants - on order
Northern Rivers Bushtucker Foods
0749 363 607
Wholesale suppliers of native seed.
Sales and enquiries:
PO Box 3022