small-scale oilseed processing - pole shift survival information

A T T R AA T T R A // SS M A L LM A L L - S- S C A L E C A L E OO I L S E E D I L S E E D PP R O C E S S I N GR O C E S S I N GP a g e P a g e 11

By Janet BachmannNCAT Agriculture SpecialistFebruary 2001

Introduction

Small-scale oilseed processing is of interest as apotential on-farm or community enterprise thatcan increase income and employment in ruralareas (1). Many seeds, nuts, and kernelscontain oil that can be extracted and used incooking, as an ingredient in other foods, as anutritional supplement, and as a raw materialfor the manufacture of soap, body and hairoils, detergents, and paints. Some of these oilsmay also be used to replace certain petroleum-based lubricants and fuels. Currently,biodiesel, which is esterified vegetable oil, hasfound a market niche because its use reducessome noxious exhaust emissions.

Small-scale oil extraction is probably more

common in other parts of the world than in theU.S. The book Small-Scale Food Processing (1),although written primarily to assist people

throughout the "developing world,"should be of interest to anyone consid-ering this enterprise.

The book contains a section on vegetableoil that provides an overview of theprocess and equipment required forextracting oil from various seeds andnuts. The book also includes a "catalog"of equipment with hundreds ofmanufacturers listed.

800-346-9140

A p p r o p r i a t e T e c h n o l o g y T r a n s f e r f o r R u r a l A r e a s

SMALL-SCALE OILSEED

PROCESSING

Abstract: This publication describes the basic processes involved in small-scale oilseed processing. Included are a low-tech method for raw material preparation using sunflower seeds as an example; information on methods and equipmentused for oil extraction; and notes on clarification, packaging, and storage. Sources for additional information and a listof suitable raw materials are provided.

ATTRA is the national sustainable agriculture information center funded by the USDA’s Rural Business -- Cooperative Service.

Contents:

Introduction .................................................................... 1Basic Steps ..................................................................... 2Sunflower Seed Oil Using the Ram Press ........................... 3Other Oil Presses............................................................. 5Adding Value Adds Costs .................................................. 6References ..................................................................... 6Resources....................................................................... 7Appendix 1...................................................................... 10Appendix 2...................................................................... 21

VALUE-ADDED & PROCESSING GUIDE


Ordering information is included in theResources section below. Another usefulpublication for anyone who wants to extract oilfrom seeds with a minimal investment ofcapital is the manual Using and Maintaining theRam Press (2) published by Enterprise WorksWorldwide.

Basic Steps

Raw material preparation

Preparation of the raw material often includesremoving husks or seed coats from the seeds,and separating the seeds from the chaff. Information about seed cleaners designed forsmall-scale operations can often be obtainedfrom agricultural research stations where small

Oil-containing seeds, nuts, kernels (from IBG Monforts productliterature.)

Apricot stones Black currant Red pepper

Avocado Jojoba Brazil nut

Cotton seed Coffee Passion fruit

Billberry Cocoa Pecan

Borage Coriander Pistachio

Stinging nettle Caraway seed Rape seed

Beech nut Pumpkin seed Castor bean

Calendula Linseed Sea buckthorn

Cashew nut Mace Mustard seed

Copra (dried coconut) Corn seed Sesame seed

Safflower Macadamia nut Soybean

Groundnut Almonds Sunflower seed

Spurge Melon seed Tropho plant

Rubber seed Poppy Tomato seed

Rose hip Nutmeg Grape seed

Hemp Evening primrose Walnut

Hazelnut Neem seed Citrus seed

Raspberry Niger seed

Elderberry Palm kernel


plot research is conducted with various crops. For instance, USDA researchers working withflax in North Dakota purchase some of theirequipment from Seedburo (3), which willsupply a catalog upon request. Almaco (4) isanother company that specializes in equipmentfor research, such as one- and two-row testplot combines and various types of stationarythreshers. Check Resources for additionalsources of equipment.

Extraction

Oil extraction can be done mechanically withan oil press, expeller, or even with a woodenmortar and pestle—a traditional method thatoriginated in India. Several types of small-scaleextractors are commercially available, bothimported from other countries and manufac-tured in the U.S. Oils can also be extractedwith solvents, but solvent extraction is acomplex operation. Appendix 1 describes andcompares various methods of extraction. Appendix 2 presents a chart with additionalinformation about the extraction and refine-ment of vegetable oils.

Clarification

Clarification removes contaminants, such asfine pulp, water, and resins. Oil can beclarified by allowing it to stand undisturbed fora few days and then removing the upper layer. If further clarification is needed, the oil may befiltered through a plastic funnel fitted with afine filter cloth. Finally, the oil may be heatedto drive off traces of water and destroy anybacteria.

Packaging and storage

Use of clean, dry containers to package andstore oils can help to prevent rancidity. Sealedglass or plastic bottles are adequate. It ispreferable if they are colored and kept in a

dark box. The shelf life of oil can be expectedto be 6–12 months if it is adequately packagedand kept away from heat and sunlight (1).

Sunflower Seed Oil Using TheRam Press

Enterprise Works Worldwide (formerly Appro-priate Technology International) (5) hassupported a number of projects in Africaprocessing oilseeds using the ram press. Thepresses are mass-produced in Zimbabwe forexport. Over 4,000 presses have been soldsince they were initially designed in 1986. Theprice in Zimbabwe is $80. Each press weighsabout 45 pounds and can process 100 to 120pounds of sunflower seeds per day. Theextraction rate is 20 to 25% using the softer-shelled, high-oil-content sunflower varieties. The ram press can also be used for sesame,mustard, and safflower seeds, and peanuts. Details on the use of the press are given inEWW’s manual Using and Maintaining the RamPress (2). The information on pressingsunflower seed that follows is from thatmanual.


Choose seed that has a soft shell and high oilcontent (40–45% oil). Most high oil contentsunflower seeds are all black. Many stripedseeds have little oil. To get some idea of howthe seed will work in the press, try to crack itopen with your fingers. This will not bedifficult with soft seed. With hard seed, youmay need to use your teeth. Now look at thekernel inside the shell. It should fill the shellcompletely. If the seed is much smaller thanthe inside of the shell, it was probablyharvested too early. You will not get much oilfrom it.

Put the kernel (without the shell) between yourtwo thumbnails and squeeze. Did the kernelfall apart? Are there little smudges of oil onyour thumbnails? If not, there may not bemuch oil in the kernel. (This is a very roughway of assessing seed. The manual alsopresents a more precise method for determin-ing the percent of oil, but encourages thepractice of checking seeds with your fingers.) Check the different batches of seed you comeacross. In time you will get a feel for thedifferences.

For successful pressing, the seed must be:

• Dry. Moist seed will lead to low yields andclogging of the cage (a part of the press). Moist seed may also get moldy.

• Clean. Fine dust in the seed may clog thecage. Chaff left in the seed will absorbsome of the oil and keep it from gettingsqueezed out of the cage. Sand in the seedwill wear the press out. Stones badly dam-age the piston.

• Warm. Warm seed will yield the most oilfor the least effort.

Seed should be dried before being bagged andstored. Very damp seed will feel humid whenyou bury your hand in it, especially if the seed

is warm. If you heat your seed in the sununder a sheet of clear plastic, you may seemoisture collecting on the underside of theplastic if the seed is too wet.

Seed that is slightly too damp may feel dry, butwill not press well. If it is too damp, but notyet moldy, it can be dried in the sun. (Neverpress moldy seed. It is not safe for humanconsumption.) Spread the seed out thinly onthe ground or on plastic or roofing tin. At theend of the day, pile the seed up to keep it fromabsorbing moisture in the cool night air andspread it out again in the morning. If there isany chance of rain or if the morning dew isheavy, you will need to bag all the seed in theevening and put it back out the followingmorning. After two or more sunny days, thehusks will have dried out. Now bag the seedand store for a week. In that time, the moisturein the seed will be drawn into the dry husk andthe entire seed will become evenly dry.

Winnowing is a low-cost way to clean the seed. On a day when there is a steady breeze,spread a cloth on the ground. Drop the seedsfrom a container to the cloth. The chaff anddirt will blow away. The seeds will collect onthe cloth. Any stones must be picked out byhand.

If the sun is shining, the seed can be heated ona piece of roofing tin or some black plastic. Spread the seed thinly and evenly on the sheet. On a sunny day it will be hot to the touch in15 minutes. The seed should be at least 104°F,which is pleasantly warm to the touch. Theyield will improve as the seed gets hotter, allthe way up to 150°F, uncomfortably hot to thetouch. The seed will heat faster on a blacksurface than on a light-colored surface. Somepeople also cover the seed with a sheet of clearplastic. This helps to hold heat in and makethe seed hotter.


If the sun is not shining, you can also heat theseeds over a heat source. Put the seeds in ashallow pan over low heat for 5 minutes. Youwill need to stir the seeds often. Be careful notto overheat the seeds on the bottom. Charredseeds will give the oil a bad taste.

Alternatively, you can use a double boiler tomake sure that the seeds are not burned. Youwill need two pots, one large and one smaller. Set the larger pot on a stove or fire withenough water to keep it from boiling dry. Setthe smaller pot inside the big pot. The bottomof the small pot does not need to touch thewater in the big pot. Put the seed in thesmaller pot, stir it occasionally, and the steamfrom the boiling water will heat the seedwithout burning it. The seed should be readyin 15 minutes.

The boiler works best if the smaller pot isalmost the same size as the big pot. Then thereis not too much room for the steam to escapefrom between the two pots. This method doesnot require as much attention and stirring andyou will not spoil any seed from accidentalcharring, but it uses more fuel.

The seed is now ready to be pressed. Thepressing operation is described in detail in themanual, complete with diagrams. Dr. RitaLaker-Ojok (6), an EWW staff person workingin Africa, cautions that training in use of thepress is important, especially in regard topressure adjustments. Correct adjustmentallows the "cake", or meal, to come out; toomuch pressure may cause a jam.

According to Dr. Ojok, the sunflower oilproduced is of very high quality. It can befurther processed, or clarified, in one of threeways. The simplest is to let it settle for a week. Alternatively, the oil can be mixed with a littlewater and salt and boiled for 10 minutes. Thischanges the taste slightly. Or the oil can be

filtered through coat lining fabric covering theopening of a pipe fit into the bottom of abucket.

Seed cake or meal, a valuable by-product

Seed cake is a valuable second product of yourpressing business. Sesame seed cake is valuableas a human food. Sunflower seed cake is notsuitable as a food for people, but it makes agood addition to chicken, pig, or cattle feed. Since sunflower seed cake has all the seed hullsin it, it is very fibrous. The ram press does notget all the oil out of the cake; it is oilier thanmost feed additives. It is quite high in crudeprotein, but contains very little carbohydrate. It should be used as a feed additive, not a feedby itself. The EWW manual describes feedrations for commercial broiler chickens, cows,and pigs that include sunflower seed cake.

Proper storage of both seed and seed cake isextremely important. Seed must be protectedfrom moisture, rodents, and insects. Verymoist seed will rot. Even if your seed is notmoist enough to rot, it may be moist enough togrow mold. This is a problem for two reasons.

• Moldy seed cake does not taste good toanimals. They may not be willing to eatmoldy feed.

• Some kinds of mold make mycotoxins suchas aflatoxin. These poisons can make peo-ple sick or give them cancer. Some of thepoisons from moldy seed will end up in theoil, but most remains in the seed cake. Poison in moldy cake can make animalssick. It can also get into the meat, eggs, andespecially the milk of the animals that eatthe cake.

Mold spores (seeds) are present in all crops. Molds grow best in warm, humid weather. To


prevent the growth of mold, seeds need to bedried before or shortly after harvest. Even dryseed can quickly get damp by being in contactwith moisture or damp earth. Once the seed is

dried and bagged, it must be stored carefully tokeep it from taking up moisture. The moisturecontent of the seed should be no higher than10%. To test for percent moisture, weigh asample of seed or cake, then heat the sample inan oven at 300°F for 1 hour. Reweigh thesample. The weight lost in the oven is equal tothe moisture content of the original sample,and the percent can be calculated: divide theweight lost by the original weight, and multiplyby 100.

Other Oil Presses

KOMET Oil Expellers

KOMET Vegetable Oil Expellers are manufac-tured by IBG Monforts in Germany (7), whoserange of products covers small hand-operatedas well as industrial machines. According totheir product literature, KOMET oil expellersfeature a special cold pressing system with asingle conveying screw to squeeze the oils fromvarious oil-bearing seeds. The machinesoperate on a gentle mechanical press principlethat does not involve mixing and tearing of theseeds. Vir-tually all oil-bearing seeds, nuts, andkernels can be pressed with the standardequipment without cumbersome adjusting ofscrews and oil outlet holes.

The vegetable oil produced needs no refining,bleaching, or deodorizing, as long as thenatural taste, smell, and color are acceptable. Generally, the sediments in the vegetable oilcan be removed by pouring the oil from thecollecting vessel into clean glass bottles after arest of approximately 24 hours after extraction. During this time, all the sediments, dust, andother impurities will have settled down on the

bottom of the collecting vessel in the form of ahard cake. In addition, the clean oil may bepoured through a paper or textile filter in orderto remove the natural slime.

Since the vegetable oil will not reach tempera-tures higher than approximately 100–120°F, allthe vital components will be preserved.Therefore, it is excellently suited for naturalnutrition. As long as the oil is stored in darkand cool rooms, it will have a long shelf life.

Preconditioning of the seeds is required prior tothe extraction process. Big nuts, kernels, andcopra (dried coconut meat) have to be crushedto the particle size of peas on the KOMETCutting Machine "System CRUSHER".

The sole representative for Monforts equipmentfor the USA and Canada is E. Peter Mathies(8). Mr. Mathies is an employee of Badger OilCompany, which is majority-owned by theWisconsin Business Innovation Corporation. He also works with the state to introduce newcrops, such as canola, hazelnuts, and caraway,to the area; expand the use of present cropssuch as sunflower for industrial, cosmetic,nutriceutical, and pharmaceutical markets; andmake oil from fruit seeds such as cranberry,raspberry, grape, and blueberry. These seeds,which have been waste products, are nowbeing promoted for the vitamins and antioxi-dants they contain.

Taby Press

The Taby Press (9) is a screw press manufac-tured in Sweden. Various models are availablefor cold pressing rapeseed, linseed, flaxseed,sunflower seed, sesame seed, peanut, ground-nuts, mustard seed, poppy seed, cotton seed,jojoba, etc. Bengt Jonsson is the constructor,manufacturer, and seller of the oilpress, and isalso a farmer.


Adding Value Adds Costs

Although value-added processing can be a wayto increase a farmer's share of the food dollar,adding value doesn't come free. At each step,the farmer is adding more work, buyingadditional equipment and supplies, and usingmore energy. Information needs increase. Anddepending upon the situation, liabilityinsurance may become a must.

A key point to remember is that adding valueto any foods by processing increases safety risksdue to the increased handling. Therefore, rulesand regulations are established by each state toprotect the public health. In addition, the FDAregulates products going out of state. Anyoneconsidering processed foods as a value-addedbusiness should contact their state healthdepartment before proceeding.

Related information from ATTRA

The ATTRA publication Adding Value to FarmProducts: An Overview introduces the conceptof value-added farm products, outlines keys forsuccess, and provides resources for additionalinformation. Evaluating a Rural Enterprise,Alternative Agronomic Crops, and Keys toSuccess in Value-Added Agriculture presentthings to consider before diversifying andmarketing alternative crops, and sources ofadditional information.

References:

1) Fellows, Peter and Ann Hampton, editors. 1992. Small-Scale Food Processing: A Guide to Appro-priate Equipment. Intermediate TechnologyPublications. 158 p. (A second edition waspublished in 2000. See Resources section forordering information.)

2) Herz, Jonathan. 1997. Using and Maintaining theRam Press. Enterprise Works Worldwide. Wash-ington, D.C. 42 p. (Contact EWW (5) for informa-tion on availability.)

3) Seedburo1022 West Jackson Blvd.Chicago, IL 60607-2990Phone: 312-738-3700, 1-800-284-5779Fax: 312-738-5329Website: www.seedburo.com

4) ALMACO99 M AvenueP. O. Box 296Nevada, IA 50201; USAPhone: 515-382-3506Fax: 515-382-2973E-mail: [email protected]: www.almaco.com

5) Enterprise Works Worldwide1331 H Street, NW, Suite 1200Washington, DC 20005Phone: 202-293-4600

6) Dr. Rita Laker-OjokEnterprise Works Worldwide (address above)E-mail: [email protected]

7) IBG MonfortsP.O. Box 20 08 53D-41208 MönchengladbachGermanyPhone: +49 - (0) - 21 66 - 86 82 - 0Fax: +49 - (0) - 21 66 - 86 82 - 44E-mail: [email protected]: www.ibg-monforts.de

8) E. Peter Matthies1400 South River StreetSpooner, WI 54801Phone: 715-635-2197Fax: 715-635-7262E-mail: [email protected]

9) Skeppsta Maskin ABBengt JonssonTaeby SkeppstaSE-70594 OerebroSwedenPhone and fax: +46 19 228005E-mail: [email protected]: www.oilpress.com/


Resources:

1. Anon. 1993. Oil Processing. IntermediateTechnology Publications. 48 p.

This book is aimed at volunteers trainingfor food processing projects and their train-ers, the non-specialist already involved inprojects and seeking specific information ontechnology choice. Contents include rawmaterials from which oil can be extracted,methods of oil extraction and processing,description of types of improved technolo-gies, case studies, checklist of questions toask when planning a project/enterprise,facts and figures on a range of pre-processing and extraction equipment, refer-ences, further reading, contacts. $15.00from:

Stylus Publications, LLCP.O. Box 605Herndon, VA 20172-0605Tel: 703-661-1581 / 800-232-0223Fax: 703-661-1501E-mail: [email protected]: http://styluspub.com

2. Anon. 1983. Small Scale Oil Extractionfrom Groundnuts and Copra. ILO Tech-nica Memorandum No. 5, MF 06-274. 111p.

A look at the steps involved in removing oilfrom peanuts (groundnuts) and dried coco-nut (copra) using small-scale mechanizedequipment, this volume should be helpful ineither starting a business or in identifyingwhere in the process technical improve-ments may be made. "It provides detailedtechnical and economic information onsmall-scale oil extraction mills using eithersmall expellers or power ghanis, and proc-essing between 100 tons and 220 tons ofmaterials per year. An economic compari-

son between these small-scale plants andmedium- to large-scale plants is provided." $15.75 plus shipping and handling from:

VITA Publications1600 Wilson Blvd., Suite. 710Arlington, VA 22209703-276-1800E-mail: [email protected]: www.vita.org

3. Boyd, John. 1995. Tools for Agriculture,3rd edition. VITA Publications. 200 p.

This new, enlarged edition of a well-knowncatalog lists over 1,000 manufacturers andsuppliers of low-cost agricultural imple-ments. Guidance is provided for selection of3,000 products, from hand tools to animal-powered and small-engine equipment. Il-lustrated. $49.50 plus shipping and han-dling from VITA. (See address above.)

4. Carruthers, Ian and Marc Rodriguez. 1992. Tools for Agriculture: A Buyer’s Guide toAppropriate Equipment for SmallholderFarmers, 4th ed. Intermediate TechnologyPublications, London, GB. 238 p.

A unique guide to small-scale farmingequipment. An expert who sets the avail-able tools against the background of goodfarming practice introduces each subject.The book analyses why some projects aresuccessful and suggests ways to improvethem. $55 from Stylus Publications, LLC. (See contact information above.)

5. ECHO17391 Durrance Rd.N. Ft. Myers, FL 33917Phone: 941-543-3246Fax: 941-543-5317E-mail: [email protected]: www.echonet.org


ECHO — Educational Concerns for Hun-ger Organization —is a non-profit, Chris-tian organization dedicated to the fightagainst world hunger. ECHO's Websiteprovides access to resources and servicesfor small farm tropical agriculture fromaround the globe. ECHO’s most popularpublications are on-line, and include severalabout oilseed crops. A for-sale publication($17.50) is The Manual Screw Press forSmall-Scale Oil Extraction.

6. Food Processing Machinery & SuppliesAssociation200 Daingerfield RoadAlexandria, VA 22314-2800Phone: 703-684-1080Fax: 703-684-1080E-mail: [email protected]: www.processfood.com

FPM&SA is a non-profit trade associationfounded in 1885 to provide a business linkbetween food and beverage processors andsuppliers. The Association is made up ofseveral hundred industry members. It canprovide information about sources of allkinds of equipment and supplies. Process-food.com is the association’s electronicmarketplace.

7. Food Protein Research and DevelopmentCenterOilseeds Processing ProgramKhee C. Rhee, DirectorCater-Mattil HallThe Texas A&M University SystemCollege Station, TX 77843-2476Phone: 979-845-2741Fax: 979-845-2744 faxE-mail: [email protected]

The mission of the Oilseeds ProcessingProgram is to conduct basic and applied re-search to help add value to oilseeds and to

serve as a technical resource to the oilseedsprocessing industry.

The Oilseeds Processing Program has ex-perience with essentially all row crop oil-seeds as well as a number of industrialcrops. Row crop expertise includes familiaredible oilseeds such as soybeans, cotton-seed, corngerm, canola, peanuts, sunflowerseed, safflower seed, and flaxseed. Indus-trial crop expertise includes castor seed,rapeseed, crambe, jojoba, and others invarious stages of commercialization. Spe-cific services include:

• Pilot plant trials in all aspects of seedpreparation, screw pressing and solvent ex-traction, and meal desolventizing andtoasting processes.

• Processing of the oil fraction, includingdegumming, refining, bleaching, hydro-genation and deodorization.

• Conversion of the meal into vegetable foodprotein flours, concentrates and isolates, orprocessing into pelleted or extruded farmanimal and aquaculture feeds and pet foods.

• Consultation, on-site process troubleshooting, development of operating andquality control manuals.

• Short courses and customized training.• Technical assistance in market development

of new crops.• Practical short courses and customized

training.

8. Huntsman, Inc2362 Warren Ave.Twin Falls, ID 83301Phone: 1-888-812-3377Fax: 208-733-2240E-mail: [email protected]: www.huntsmaninc.com

Huntsman, Inc. supplies used and recondi-tioned food-processing equipment, includ-ing seed cleaners and packaging.


9. Judge, Emma et al. (ed.) 2000. Small-ScaleFood Processing, 2nd Ed. IntermediateTechnology Publications. 184 p.

This guide provides development workersand small-scale entrepreneurs with the ba-sic information and advice that they needto set up a small-scale food processing en-terprise. Part one considers the food proc-esses that are suitable for different crops in-cluding fruit and vegetable products, cerealand pulse-based products, milk and milkproducts, and meat and fish products. Parttwo is an annotated directory giving theappropriate equipment needed to process aparticular food, an index of manufacturers,the approximate costs, and the names andaddresses of manufacturers. The potentialuses of equipment are examined and muchof the equipment is clearly illustrated.

In this new edition the main text whichguides the reader through the stages offood processing activities has been reor-ganized and clarified, and the catalog sec-tion, listing suppliers in approximately 50countries, has been completely updated. $55 from:

Intermediate Technology Publi-cations103/105 Southampton RowLondon WC1B 4HHUKE-mail: [email protected]: www.oneworld.org

10. Logsdon, Gene. 1977. Small-Scale GrainRaising. Rodale Press, Emmaus, PA. 305 p.

In addition to covering production of alarge number of grains, information is pro-vided on harvesting, storage, grinding andcooking. Out of print, but may be found ina library.

11. Potts, Kathryn H. and Keith Machell. 1995. The Manual Screw Press for Small-ScaleOil Extraction. Intermediate TechnologyPublications. 72 p.

This practical handbook describes the fullprocess of oil production with a manualscrew press (also known as the bridge pressor spindle press.) The process is detailedstep by step, including health and safetyguidelines, equipment requirements, main-tenance procedures, and approaches tosales and marketing. Appendices cover re-cord keeping, financial considerations, andthe use of a roller mill to speed up crush-ing, which is one of the essential prepara-tory stages for maximum oil production. $17.50 from Stylus Publishing, LLC. (Seecontact information above.)

12. Producers' Natural ProcessingPurdue Research Park1291 Cumberland Ave.West Lafayette IN 47906Phone: 765-563-3437Fax: 765-563-6753E-mail: [email protected] (Bob Leader)Website: www.pnpi.com

Although most of the small-sized oil seedpresses seem to be manufactured in Europe,Bob Leader of Producers’ Natural Process-ing (PNP) provides connections fromaround the U.S. on the cold press expellermethod of seed oil extraction, which doesnot use volatile solvents. PNP does not sellequipment, but does have informationabout where to obtain new and usedequipment. There are two PNPs. One is an“S” corporation that is owned by inde-pendent press operations around theUnited States, the other is a “C” corpora-tion. The “C” corporation consists mainlyof researchers in gene technology, func-tional foods, and pharmaceutical products. It does consulting work for food processors(especially in the use of non-solvent ex-


tracted ingredients) and has partnershipswith major life science companies, bakeries,and cooperatives. The “S” corporation is ashareholder of the “C” corporation.

13. Richards, Keith and Deborah S. Wechsler. 1996. Making It On the Farm: IncreasingSustainability Through Value-added Proc-essing and Marketing. Southern SustainableAgriculture Working Group. 40 p.

This booklet is written for farmers whowant to take a bite out of the middlemen bybringing the dollars for processing, pack-aging, labeling, and marketing home totheir farms, and for local community lead-ers who want to encourage farm-basedvalue-added businesses in their communi-ties. Compiled from interviews withSouthern farmers and ranchers who areadding value to their products, it describessome of their practices, discusses 10 keys tosuccess, and includes a list of resources. Although some of the resources listed are inthe Southern region, most have counter-parts in other states and regions. Cost is$12, payable to SSAWG, and includesshipping and handling. Order from:

Southern SAWG PublicationsP.O. Box 324Elkins, AR 72727

By Janet BachmannNCAT Agriculture Specialist

February 2001

APPENDIX I

TECHNICAL PAPERS

The papers that follow are slightly condensedfrom two of a series published by Volunteers inTechnical Assistance to provide an introduc-

tion to specific state-of-the-art technologies ofinterest to people in developing countries. Thepapers are intended as guidelines to helppeople choose technologies that are suitable totheir situations. They are not intended toprovide construction or implementation details. People are urged to contact VITA or a similarorganization for further information andtechnical assistance if they find that aparticular technology seems to meet theirneeds.

VITA is a private, nonprofit organization thatsupports people working on technical problemsin developing countries. VITA offers informa-tion and assistance aimed at helping individu-als and groups to select and implementtechnologies appropriate to their situations. VITA maintains an international InquiryService, a specialized documentation center,and a computerized roster of volunteertechnical consultants; manages long-term fieldprojects; and publishes a variety of technicalmanuals and papers.

UNDERSTANDINGPRESSURE EXTRACTION OFVEGETABLE OILS

By James Casten and Dr. Harry E. Snyder

Uses Of Vegetables Oils

Since the beginning of history, people havemade use of the oils obtained from seeds andnuts.

The principal use of these oils is as food. Theyare eaten raw and cooked, are a usefulingredient in baking, and serve as a means oftransfer of heat in frying. Oils are a source ofcalories and of fat-soluble vitamins.


Oils also have a number of nonfood uses. Theyserve as lubricants, and as a drying base forpaints. They are boiled with alkali to makesoaps, and are an ingredient in many cosmet-ics.

Vegetable Sources Of Oil AndFat

Commercial Nuts and Seeds Used for Oil

The table below lists the seeds most commonlyused commercially to obtain oil by means ofmechanical pressing. *

* Soybeans are not included in the list because their oilcontent of only 20 percent makes it impractical to extract oilfrom them by mechanical pressing. Soybean oil is recoveredby solvent extraction.

Commercial Nuts and Seeds Used for Fat

Vegetable fats are semisolid at room tempera-ture, whereas oils are liquid. Fats have ahigher melting point than oils, and thus areheated before pressing. The table below listscommon sources of vegetable fats.

Methods Of Extracting Oil FromNuts And Seeds

Oil can be extracted from nuts and seeds byheat, solvents, or pressure. Extraction by heatis not used commercially for vegetable oils. Nathan Kessler deals with extraction bysolvents in Understanding Solvent Extraction ofVegetable Oils in this same series below. Thispaper deals with extraction by pressure.

Pressure extraction separates the oil from thesolid particles by simply squeezing the oil out ofthe crushed mass of seeds. The simplestmethod is to fill a cloth bag with ground seedpulp and hang the bag so that it can drain.

Seed Oil Content (%) UsesAlmond 50 Food, salad oil, soapCastor 50 Medicine, lubricant

Cotton seed 30 Food, paint, resinHemp seed 35 Paint, varnish, soapLinseed 40 Paint, soap, varnish, linoleumOlive 40 Salad oil, cooking oilPeanuts (groundnuts) 50 Salad oil, cooking oilPerilla seed 50 Drying oil for paint, resinPoppy seed 50 Salad oil, cooking oilRape seed (colza) 40 Salad oil, cooking oilSesame seed 50 Salad oil, cooking oilSunflower seed 35 Salad oil, cooking oil, soapTung nuts 20 Paint

Seed Fat Content (%) UsesCocoa (cocoa) butter 40 Chocolate, foodCoconut oil from copra 50 Food, chemicals, soapHahua (illipe) butter 60 Food, candles, soapJapan wax 30 Lubricant, leather dressingPalm nut oil 50 Food, chemicals, soapShea butter 55 Food, candles, soap


Some of the oil, called free run oil, flows out;the rest must be pressed out mechanically. Thesimplest way is

by placing heavy rocks on the materials. Orbags of oil seed pulp can be placed one aboveanother in a box or cylinder, and greatpressure can be slowly brought to bear on thewhole mass. A long lever can exert up to 100pounds per square inch.

Since greater pressure provides greater oilrecovery, heavy and strong mechanical jacks ofseveral designs (screw jacks, ratchet jacks, andhydraulic jacks) have often replaced the lever. A 20-ton jack can exert 1,000 pounds persquare inch on a small cylinder of seeds.

Batch Presses

A batch press processes one batch of seeds at atime. Batch presses range from small, hand-driven presses that an individual can build topower-driven commercial presses capable ofprocessing many tons of seeds a day.

Small Batch Presses

Small batch presses are simple, but inefficient. However, they do work. They can be used inremote areas and can help determine whether

there is a market for oil produced locally. Fewresources are needed for an operation on thisscale: wood fires for heating, and hand laborfor pressing. Much hand labor is required toproduce a small amount of oil this way.

If you plan to build a press in a remote areausing only wood or locally available materials,VITA can send you some papers aboutprocessing oil seeds.

Advantages of small batch presses:

• They can be made of locally availablematerials.

• They can produce a good quality product.• They are easy to repair.• Their cost is low.• They do not require trained operators.

Disadvantages of small batch presses:

• They are labor intensive.• Complete recovery of the oil from the seeds

is difficult. If seeds are plentiful, this is nota serious problem.

Commercial Batch Presses

Once a business is started, the market and cashflow may grow quickly. If that happens, thesimple equipment just described may beoutgrown. You must then get information onlarger equipment from commercial sources. The smallest commercial presses cost severalhundred U.S. dollars and are hand-operated. Write to manufacturers for price and size.

If electric power is available, hydraulic pressesare available for any capacity required. Whenwriting to a manufacturer, describe the kind ofseeds or nuts that are available and the amountyou plan to process. Also give the type ofelectricity available, 50 cycle 220 volts forexample.

At this scale of operation, seed storage anddisposal of oil cake need to be consideredcarefully.

Hydraulic presses, which are suitable only forbatch processing, may be powered either byhand or by electricity. In many parts of theworld, they are the most practical andeconomical way to extract oil from seeds.


A hydraulic press is simple in operation. Theground seed material or wet plant tissue isplaced in the press in layers, with each layerseparated from the next by a press cloth. Pressure is applied, slowly at first, and thenincreased as the oil content in the tissuedecreases. Maximum total pressure is 2,000pounds per square inch for one inch layers. Total time to load the press, apply the pressure,and remove the cake, is approximately onehour. Drainage of the oil while under pressuremay require 30 to 45 minutes. The amount ofraw material that can be handled depends onthe size of the press, which in turn depends onwhether it is a hand press or is operated byelectrical power.

Advantages of commercial-size batchpresses:

• They can be driven by hand or by electric-ity.

• They are economical to operate.• They are simple to operate and maintain.• Operators require only minimum training.• Recovery of oil from seeds is excellent.

Disadvantages of commercial-size batchpresses:

• The cost of the machinery is substantial,and delivery time may be long.

• Spare parts are difficult to obtain in remoteareas (though they can be airmailed almostanywhere).

• Electric power, or generators to produce it,must be available to operate the largermodels.

Expellers Or Continuous ScrewPresses

Expellers, or continuous screw presses, areused throughout the world for the expressionof oil

from copra, palm kernels, peanuts, cottonseed,flaxseed, and almost every other variety ofseed, wherever there is a large enough seedsupply to justify a continuous operation.

Expellers achieve the pressure needed toexpress the oil by means of an auger that turnsinside a barrel. The barrel is closed, except foran opening through which the oil drains.

An expeller can exert much greater pressure onthe seed cake than a hydraulic batch press can. This increased pressure permits the recovery ofa larger proportion of the oil: generally, about3 to 4 percent of the oil is left in the cake withan expeller, compared to 6 to 4 percent with ahydraulic press. The expeller is an essentialpart of almost all modern oil seed extractionplants. It is used both by itself and as a pre-press before solvent extraction. Expellers varyin size from machines that process 100 poundsof seed per hour, to machines that process 10or more tons of seed per hour.

Advantages of expellers:

• They are the most common type ofmechanical extraction equipment in usecommercially today.

• They require less labor than any othermethod.

• Where power is reasonable in cost, andlabor is expensive, continuous expellers areeconomical.

• Plant capacity is higher than with batchequipment.

• Expellers extract a greater proportion of theoil than do hydraulic batch presses.

Disadvantages of expellers:

• Equipment must be purchased.


• Maintenance costs are high, and mainte-nance requires skilled mechanics. It isalways best that the chief mechanic be sentto the machinery supply factory for train-ing.

• More energy is required than for batchprocessing.

• Electric power is required for the press andfor auxiliary equipment.

• The press must operate continuously for atleast eight hours; intermittent operation isunsatisfactory.

• Oil from an expeller has more impuritiesthan oil from a batch press, and must beheated and filtered to obtain a clean oil.

Choosing Your Method

The type of press that is appropriate dependslargely on the size of the operation. Oilprocessing operations range in size fromcottage industries processing only a fewpounds of seed per day, to factories processingas much as 3 or 4 thousand tons of seed perday.

For small operations (processing less than 1 tonof seed per day), the right equipment is almostalways a form of batch press.

If 1 or more tons per day are to be pressed, theright equipment is most often an expeller.

SEQUENCE OF OPERATIONS

The sequence of operations in processing oilseed for pressing is as follows:

Storage

The seeds, nuts, or plant tissue containing theoil must be properly stored and prepared forextraction, to maintain high quality in the finalproduct.

If the oil-bearing material is dry, it must bestored so that it remains dry, for optimumextraction and quality of the oil. If the oil-bearing material is wet plant tissue, it should beprocessed for oil-extraction as soon as possibleafter harvest so that storage time is kept to aminimum. Oils in the presence of waterdeteriorate rapidly, forming free fatty acids andrancid off-flavors.

Cleaning

After the oil-bearing materials have beenremoved from storage, the first step inpreparing them for oil extraction is to cleanthem. The cleaning is done so that the oil is notcontaminated with foreign materials, and sothat the extraction process can proceed asefficiently as possible.

Inspect the seeds carefully and remove stones,sand, dirt, and spoiled seeds. Dry screening isoften used to remove all material that is over orunder size. Washing is possible, but it isimportant to try to avoid wetting tissue thatwould have to be dried later.

Dehulling

After raw material has been cleaned, it may benecessary to remove its outer seed coat. Thereare a couple of reasons for doing this. The seedcoat does not contain oil, so including it makesextraction less efficient. Also, the next step willbe grinding to reduce particle size, and anytough seed coats interfere with this process.

Some seeds, such as peanuts, can be shelled byhand. Some others, such as sunflower seeds,are usually hulled in machines. Still others, likesafflower and colza, cannot be shelled. If thereis no problem in grinding the seed, it may beleft on.


Grinding or rolling

Seed is not usually pressed whole, since oilextraction is more efficient if the seed is insmaller particles. Grinding the oil seed is oneeffective way to reduce particle size. A hand-operated mortar, millstone grinder, or even akitchen meat grinder can be used to convert theseeds to a coarse meal. Small hammer mills,motor or hand-powered, are also good.

Another way to reduce particle size is to rollthe oil seeds to produce flakes for extraction. Many commercial extraction plants find thisthe most effective approach. With large oilseeds it may be necessary to grind the seed first,and then put the pieces through flaking rollers.

Either process makes the actual pressing moreefficient. The final piece size that leads to mostefficient extraction can best be determined byexperiment, as the size will vary depending onthe kind of seed and the kind of pressingoperation. Generally, smaller-size pieces arebetter for oil removal. But if the pieces are toosmall, they may contaminate the oil and bedifficult to remove from the final product.

Heating

A final step in raw material preparation isheating the ground or flaked oil seed. Theexact reason that heating improves oilextraction is unknown, but it does increaseyields. Also, heating is useful if there areenzymes in the plant tissue that have adeteriorating effect on the oil quality. If the oilseed cake (that is, the residue remaining afteroil removal by pressing) is to be used for feed orfood, heating may be useful in increasingprotein availability.

Sometimes oil-bearing material is pressedwithout being heated. Oil extracted in thisway is called cold press oil.

Pressing

The materials prepared in these ways arepressed, usually in a lever press, hydraulicpress, or expeller, to remove the oil.

Refining

Cold press oil can be of such high quality as toneed no refining if it comes from seeds that arefresh and of good quality.

All other oil, especially that which has beenpressed from lower quality feedstock, is likelyto have some undesirable cloudiness, color, orflavor that needs to be removed.

Removal of Cloudiness

Pressed oils need to be filtered to removeparticles from the pressing operation, if the oilis to be clear and clean.

If gums precipitating cause the cloudiness, thegums can be removed by washing the oil withabout 2 percent water. For this process to beeffective, the oil should be heated, and the hotoil mixed with water, with active stirring. Nextthe water and oil must be separated. For this, acentrifuge is most effective. Heating to driveoff all moisture, for the reasons cited previ-ously, should dry the degummed oil.

Removal of Excess Color

For the removal of excess color, bleachingearths are effective. The oil is heated andmixed with 1-2 percent of its weight of aneffective bleaching earth purchased from areliable supplier for this purpose. After acontact time of approximately one hour, thebleaching earth is separated by filtration. Activated carbon can also be used.


Removal of Unwanted Flavors

Unwanted flavors are more difficult to remove. They may be due to excessive free fatty acids. If the oil-bearing material is stored at a highmoisture level, or if they material is bruised orbroken or moldy, it becomes more difficult topress, and the free fatty acid content of the oilextracted from it usually increases. Free fattyacids in fresh olive oil vary from 1/2 of 1percent to 3 percent. Acidity of over 10percent is common; if over 20 percent acid, theoil is good only for making soap.

Free fatty acids can be removed from the oil bywashing the oil with alkali: put 25 to 30gallons of the rancid oil in a 55-gallon steeldrum with an open top. Add 15 gallons ofwater with 2 1/2 pounds of soda ash dissolvedin it. Mix well with a big wire whip or paddleto mix the oil and water solution. The fattyacid will react with the soda to form soap,which stays in the water phase.

Let the layers separate for several hours andsiphon off the oil layer. If the oil still containsfatty acids, you should repeat the operation. There will be a loss in volume because the freefatty acids may account for 10 to 20 percent ofthe original volume. If emulsions form, youcan heat the mixture, which will usually causea separation. It is a good idea to heat therefined oil to drive off any remaining water. This method works well without your needingto send the oil to a laboratory for analysis todetermine how much soda ash to add. Anexperienced operator is the best substitute for achemical laboratory.

It is important to use clean equipment, so washall the utensils well at the end of the day. Also,allow no copper in the plant. Copper andcertain other heavy metals cause undesirablechanges in oils. For example, heating butter ina copper vessel will quickly impart a fishy taste

to the butter. Even a copper bolt in a press candamage the flavor of your product. Use castiron, or stainless steel, but no copper or copper-bearing materials.

Other types of flavors than those of fatty acidscan be removed from oil, but an expensive anddifficult process known as deodorization isused. It involves distilling off the unwantedflavors under high heat and high vacuum. Normally the oils being processed by small-scale pressing would have the flavors of theraw material from which they came, and therewould be no need for deodorization.

Final Considerations

One of the best sources of information about oilpressing on a small scale is the small oilprocessor in the region of interest. Very seldomwill an oil processor be the first in a region toattempt oil extraction. Locate those individualsalready in the business of extracting oil fromvegetable materials and learn what kinds ofequipment and raw materials they have hadsuccess with, and what kinds of problems theyhave run into.

In remote villages where oil seeds are plentiful,but mechanics and machinery are not, a leverpress or hydraulic press can be a convenientmeans of supplementing expensive importedcooking oils.

Commercial-scale edible oil production,however, is not a cottage industry. Theextraction and refining of oils and fats suitableeven for local markets is a highly technical andcapital intensive process. It is large, efficientplants that are the ones likely to make areasonable profit. The vegetable oil extractionindustry is a highly competitive commodityindustry in which the price of oil is establishedand the price of oil seeds fixed by the commod-ity market. If domestically grown oil seeds are


exported, then a local oil press will have to paythe same price for seeds as its foreign competi-tors do. The small local firm's costs of doingbusiness are likely to be as high or higher thanthose of its competitors abroad. Tariffs orsubsidies may be required to protect the homeindustry. An expeller plant can sometimesallow a small country to become independentof imported oils, but the cost of the oilextraction plant may be higher than the cost ofthe imported oils.

Glossary

Free run oil: The natural accumulation anddrainage of oil from seed pulp, without the useof a press.

Oil cake: The residue left after pressing.

Dry screening: The manual removal of under-or over-sized seeds before pressing.

Cold press: The pressing of oil bearing seeds,pulp, or cake that have not been heated.

Emulsions: Any colloidal suspension of a liquidin another liquid.

UNDERSTANDINGSOLVENT EXTRACTION OFVEGETABLE OILS

By Nathan Kessler

INTRODUCTION

Oil is extracted from seeds, beans, and nuts foruse as cooking or salad oil; as an ingredient inpaint, cosmetics, and soap; and even as fuel.

Historically, such oils have been extracted bywrapping seeds in cloth, and then using

devices operated by stones and levers to exertpressure on them.

An improved form of mechanical device,which allowed considerably more pressure tobe exerted, involves the use of hydraulicallyoperated rams: a simple, hand-operatedcylinder pump is used to press flat plates orhollow cages attached to the hydraulic ramagainst a fixed-position ram.

This type of press developed into a motorizedhydraulic pump system that pressed the seedbag and then released a press cake.

The next improvement in extracting oil was thescrew press or expeller. Screw presses use anelectric motor to rotate a heavy iron shaft,which has flights, or worms built into it to pushthe seeds through a narrow opening. Thepressure of forcing the seed mass through thisslot releases part of the oil, which comes outthrough tiny slits in a metal barrel fittedaround the rotating shaft. Expellers have acontinuous flow of seed through the machinein contrast to the hydraulic system describedabove, which uses small, individual packagesor batches of seed. To release as much oil aspossible, the seeds must be dried to rather lowmoisture content and exposure to hightemperature causes darkening of the oil. It alsocauses some scorching or overheating of themeal. The meal contains protein which, ifundamaged, may be used for either humanfood, soy flour for example, or animal feedsuch as soybean meal.

Because most press or expeller processesoverheat the meal and leave too much of thehigh value oil in the seedcakes, methods ofextracting the oil with solvents were developed. Seeds (like soybeans) with low oil content areprocessed by solvent methods alone. In othercases, presses are used first to extract part of


the oil; then solvents extract the oil thatremains in the seeds.

Because of their efficiency, processes employingsolvents to extract vegetable oils in largequantities are in wide use, and solventextraction equipment is readily availablecommercially. The basic technology of solventextraction is simple, but great care should betaken in deciding whether and where it can beused.

Solvent extraction of vegetable oils, whichrecovers more oil than earlier methods andleaves more usable meal, begins to be economi-cally attractive where large quantities of seedcan be processed (at least 200 tons per day forcontinuous-feed processes); where storage,transportation, power, water, and solventsupply are adequate; and where occupationalsafety and training standards can be enforced. There are solvent extraction plants withcapacities of up to 4,000 tons per day.

OPERATING PRINCIPLES

Solvent extraction is simple in principle, butcomplex in operation.

The seed is prepared by being cracked intochips. These chips are warmed and passedthrough smooth flaking rolls. The flaking rollsflatten the chips into paper-thin, flat flakes. The thin flakes can then be treated withsolvent, which dissolves or washes the oil outof them. Solvents that boil at fairly lowtemperatures (65°C) are used so that thesolvent can be readily removed from both theoil and the flakes. Solvent extraction recoversalmost all the oil, leaving only one percent orless oil in the flakes.

Unfortunately, most solvents are dangerous tohandle, more so than gasoline. They burn orexplode very readily. Therefore, the equipment

that extracts the oil and removes the solventmust be airtight and leakproof, and all motorsand electrical switches, lights, etc. must bespecially designed as vapor-explosion-proof. No matches, no smoking, and no cuttingtorches, welders, grinders, or other heat-producing or spark-producing devices can bepermitted where such solvents are used. Careless exposures to sources of fire or sparks(including engines of trucks driven too close toextraction plants) have caused disastrousexplosions.

Attempts to find solvents that are not explosiveand are economical to use have not yetsucceeded. Chlorinated hydrocarbons such astrichloroethylene worked well but were foundto create a poisonous by-product in theextracted meal. Solvent extraction plants builtin 1950 using trichloroethylene had to bediscarded or converted to the commonly usedexplosive solvent, hexane. Today, all commer-cial oilseed extraction plants utilize hexane or asimilar solvent.

DESIGN VARIATIONS

Like pressing, solvent extraction can be donewith equipment that processes the oilseed inbatches, or with equipment that processes itcontinuously. A continuous extractor is notconsidered economically practical unless itprocesses at least 200 tons per day.

BATCH SOLVENT EXTRACTION

Batch solvent extraction is likely to be theappropriate method if you plan to process lessthan 200 tons of seed per day, but enough toyield oil in commercial quantities.

Very few batch plants are in use in the UnitedStates today. A batch solvent extraction plantcan be as simple as an enclosed steel tank witha false bottom made of screen or metal slats.


The flakes are dropped into the tank, wherethey lie on the false bottom. The tank inlet isclosed, and solvent is pumped into the seed for10 to 20 minutes; then the drain valve at thebottom (under the false bottom) is opened tocomplete the extraction.

After the final extract has been fully drained,steam is introduced into the bottom of theextractor. This evaporates the solvent out ofthe flakes. This combination of steam andsolvent is piped as vapor into a condenser thatcontains water-cooled tubes. The solvent islighter than water, so it is readily freed ofwater by standing in a tank from which wateris decanted, or overflowed. The flakes now arenearly solvent free, but are wet from the steamtreatment. They are conveyed out of theextractor to a steam-heated dryer to reduce themoisture to about 12 percent for best storagequality. Most of the washes, or miscellas, aresaved and reused on a later batch. However,fresh, oil-free solvent must be used for the finalwash of a batch. And the first, oiliest miscellais pumped to a steam-heated, tubular evapora-tor, which boils most of the solvent out of themixture, recovering solvent for reuse. The oilthen goes to a vacuum stripper, where it isheated to about 100°C and steamed as it passesdown through a series of steel baffles or acolumn of stoneware rings or saddles. Thepurpose is to expose every portion of the oil tosteam, which is needed to remove the last 5 to10 percent of the solvent from the oil.

CONTINUOUS SOLVENT EXTRACTION

Continuous extractors use conveyors insidevapor-tight housings. The conveyor may be anendless metal mesh belt or a series of sieve-bottom buckets attached to a traveling chain.

Another style uses vertical columns filled withsolvent. Flakes are continuously fed at the top

and removed from the bottom by a verticalmass-flow elevator. Fresh solvent enters at thebottom, and oily miscella overflows from thetop. Still another style uses a rotating carouselarrangement of the extraction baskets orbuckets as in the Rotocel: this French Oil MillMachinery Company stationary extractorrotates the inlet and outlet assembly above andbelow stationary sieve-bottom baskets.

In all of these extractors, flaked seeds areconveyed continuously into the extractorthrough a vapor lock or seal that preventssolvent vapors from escaping out of theextractor into the flake conveyor. The flakesare sprayed or wet with miscella as they enterthe extractor, and receive several washes withsuccessively more dilute (less oily) miscella. These miscellas drain down through the flakesand through the sieve bottom or belt into pans,which drain into pumps. The pumps transferthe miscella to the next state, from less oily tomore oily flakes. In this continuous counter-current, the oldest solvent miscella (the solventmiscella with the highest oil content), contactsthe fresh incoming flakes. The final wash usesoil-free hexane. The flakes are then drained (10to 15 minutes), and dropped from the belt orthe basket into a spent-flake hopper.

From here a mass-flow conveyor lifts the stillsolvent-wet flakes (containing 35 percentmoisture) and delivers them into a desolven-tizer-toaster. This is a steam-jacketed vessel,usually a vertical set of kettles with gates thatallow the flakes to fall from one kettle into thenext below while being treated with directsteam. The lower kettles act as dryers to bringthe moisture content down to proper levels. Air is drawn to cool the dried hot flakes, eitherin the lower part of the same vessel or in aseparate meal cooler. As in the batch extractorsystem, the solvent vapors flow to a condenserwith water-cooled tubes, and the liquid solventis separated from the water by decanting.


An older form of desolventizer employs a seriesof steam-jacketed paddle conveyors to evaporatemost of the solvent. The partially desolventizedflakes then crop into a larger conveyor, intowhich direct steam is blown, removing the restof the solvent. This form of desolventizationwas improved by using super-heated hexanevapor to quickly remove most of the solvent. This first step is followed by a steam treatment. However, neither of these methods cookssoybean flakes thoroughly enough to eliminatetrypsin inhibitors. For this reason, if the flakesare going to be fed to nonruminant animals, acooking or toasting stage has to be added: theflakes are heated to about 125°C, reducing theirmoisture to 18 percent or less. When the flakesare intended for human consumption, this stepis not necessary, since they will be cooked beforebeing eaten.

Solvent in continuous systems is evaporatedand recovered from the miscella in the sameway as in batch systems. However, whensolvent is removed from the flakes by thedesolventizer-toaster method, the hot vaporsfrom the toaster can be used as the heat sourcein the first-stage miscella evaporator. Thisresults in important energy savings.

For seed very high in oil, such as cottonseed,groundnut or peanut, or sunflower, low-pressure expellers are usually used to removepart of the oil at reduced cost. This is followedby flaking and solvent extraction as describedabove. This pre-pressing is important in

cottonseed also because it reduces theantinutritional gossypol material left in themeal.

FACTORS TO CONSIDER IN PLANNINGAN OIL EXTRACTION SYSTEM

Solvent extraction of vegetable oils should beseen as part of a technological and economicsystem that includes far more than theextraction plant itself. Factors affecting theoperation of a solvent extraction plant include: potential markets; nature, timing, size, andreliability of seed and solvent supply; ade-quacy and reliability of power, water, andtransportation, and of maintenance andstorage facilities; and ability to find and trainpersonnel and rigorously enforce safetystandards. Table 1 gives information aboutsome of these requirements.

SIZE OF OPERATION

The size of the operation is the most importantfactor in determining which kind of processwill be used.

For intermediate-scale operations (operationsthat process up to 200 tons per day), the choiceis between batch solvent extraction andexpeller (pressure extraction) systems. Batchsolvent extraction systems operate more slowlyand less efficiently, are more labor intensiveand dangerous, and use greater quantities ofsolvent than properly designed continuoussystems do. Because of these drawbacks,

Table 1. Estimated Requirements for Solvent Extraction of Vegetable Oils, ComparingBatch and Continuous ProcessingInputs required perton of seed processed

Units Batch processing Continuousprocessing

Steam kilograms 700 280Electricity kilowatt hours 45 55Water cubic meters 14 12Solvent kilograms 5 4Labor person hours 0.8 0.5Source: Ernesto Bernadini, Batch and Continuous Solvent Extraction, Journal of theAmerican Oil Chemists’ Society 53 (Hybe 1976): 278.


expellers are usually preferred for installationstoo small for continuous solvent systems. However, there are instances when expellerextraction is not suitable for a small operation;in those cases, batch solvent extraction may bethe only practical way to proceed.

Continuous solvent extraction should beconsidered only for systems that will treat 200tons or more of seed per day.

SITE AND DESIGN

Solvent extraction plants are complex systemsthat must be carefully engineered for safetybecause of their special hazards. Because ofthe danger of explosion, solvent extractionplants need to be located a safe distance awayfrom populous areas, and to be designed byexperienced engineers. Installation of a plantwithout such engineering of details is adangerous error.

COST

The cost of solvent extraction plants is muchhigher than the cost of expeller extractionplants, usually about double. However, since asolvent plant recovers a greater proportion ofthe oil, it may still be the economically wiserchoice. For example, solvent extraction shouldrecover about 40 kilograms more oil per tonfrom dry soybeans than expeller extractionwould.

PRODUCT QUALITY

Not only does solvent extraction yield more oil,it avoids the overheating of the oil and mealthat often occurs with expeller extraction. Solvent-extracted meal can be toasted tooptimum food or feed quality.

PERSONNEL AND SAFETY

It takes less labor but more sophistication tomaintain and operate a solvent extraction plantthan to maintain and operate an expeller plant. Two people per shift are required for theformer, compared to three for the latter. Thedangers of solvent explosion make tightlycontrolled procedures necessary. Workersmust be trained to have a wholesome fear ofexposure to the solvent and of solvent leakage.

RELIABILITY OF THROUGHPUT

For continuous solvent installations especially,it is essential to be able to depend on a steadythroughput. Unscheduled interruptions ofproduction, or discontinuities because of theinability to transport the finished product, forexample, mean that seed will pile up some-where and possibly spoil, especially if storagearrangements are insufficient. Unanticipatedinterruptions of seed supply may cause buyersof oil and meal to turn to more reliable sources. Both batch solvent and expeller operations areless vulnerable to the effects of such interrup-tions than continuous solvent operations are.

INTENDED USE OF THE OIL

Since crude oil is usually refined before beingused as food, it is necessary to have a crude oilrefinery that can handle the volume of oilproduced by the extraction plant. Food oilrefineries are more complicated to operate andmore expensive in equipment costs than solventextraction plants are. For nonfood uses, suchas drying oil, a refinery is not necessary.

GLOSSARY

Expeller: A kind of screw press (see below)

Flakes: Thin, flat pieces of seed or press cake(see below) prepared for solvent treatment.


Flights: Also termed worms--the screw threadsin an expeller or screw press.

Miscella: Also termed wash--the liquid,containing oil and solvent, drained afterapplication of solvent to flaked seeds.

Press cake: Seed residue left after pressing.

Screw press: A press that uses a screw to guideand force seeds through a narrow opening.

Trypsin Inhibitors: Enzymes that prevent thebreaking down of proteins.

Wash: Also termed miscella. The liquid,containing oil and solvent, drained afterapplication of solvent to flaked seeds.

Worms: In a screw press the screw threads, orflights, that guide and force seeds through anarrow opening.

APPENDIX II

Frontier Herbs is a natural foods cooperative. The chart below contains information aboutthe extraction and refinement of Frontier’svegetable oils from the company’s WholesaleProduct Catalog.

Less refined oils are best for cosmetic uses suchas massage, bath or facial oils because they arenutrient-rich and free of additives. Sediment iscommon is less refined oils and is considerednormal. In cooking, less refined edible oils havemaximum flavor and aroma. However,unrefined vegetable oils are fragile, with limitedshelf life. Therefore, some degree of refinementis necessary to ensure a usable product. Allvegetable oils should be stored in a cool, darkarea.

Winterized—A chilling and filtration processthat removes heavy, less stable fats and waxes.

Bleached—The oil is treated with compoundssuch as activated clay to remove substances,including chlorophyll, that can discolor the oil.Deordorized—Undesirable flavor and odorcompounds are removed by aerating the oilwith steam.Filtered—Particles, such as plant cells left inthe oil after the extraction process, areremoved.

The Electronic version of Small-Scale OilseedProcessing is available at:HTMLhttp://www.attra.org/attra-pub/oilseed.htmlPDFhttp://www.attra.org/attra-pub/oilseed.pdf


Frontier Natural Products Co-op3021 78th St., P.O. Box 299Norway, IA 52318Phone: 1-800-669-3275Website: www.frontierherb.com

IP134

Name Method of Extraction Method of Refinement

Almond, sweet Expeller Pressed Refined, Bleached, Winter-ized, Deodorized

Apricot Kernel Expeller Pressed Refined, Bleached, Winter-ized, Deodorized

Castor Expeller Pressed FilteredCocoa Butter Expeller Pressed FilteredCoconut Expeller Pressed Bleached, DeodorizedGrapeseed Solvent Extracted Refined, Bleached, Deordor-

izedJojoba Expeller Pressed FilteredOlive, Extra Virgin Expeller Pressed UnrefinedRosehip Seed Expeller Pressed FilteredSesame Expeller Pressed UnrefinedShea Butter Expeller Pressed Unrefined

The ATTRA Project is operated by the National Center for Appropriate Technology under a grant from the RuralBusiness-Cooperative Service, U.S. Department of Agriculture. These organizations do not recommend or endorseproducts, companies, or individuals. ATTRA is located in the Ozark Mountains at the University of Arkansas inFayetteville at P.O. Box 3657, Fayetteville, AR 72702. ATTRA staff members prefer to receive requests forinformation about sustainable agriculture via the toll-free number 800-346-9140.

small-scale oilseed processing - pole shift survival information

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