当前位置：文档库 › 储粮

储粮

Storage and drying of grain in Canada:low cost approaches

Digvir S.Jayas *,Noel D.G.White

Department of Biosystems Engineering,University of Manitoba,Winnipeg,MB,Canada R3T 5V6Received 11November 2001;received in revised form 7January 2003;accepted 9January 2003

Abstract

Most Canadian grain (>70%of harvests)is stored on the farm.High moisture content of grain at harvest rapidly leads to spoilage and occasionally the production of the mycotoxins sterigmatocystin,ochratoxin A,or citrinin.Near ambient drying systems that consist of an electrical fan at the base of a granary blowing air into a plenum beneath a perforated ?oor under stored grain is relatively economical.Heat produced by the fan can dry grain by 2%moisture content in 2months at a cost for electricity of Can.$0.87/tonne.Hot air dryers are used on wet grain at harvest to rapidly lower 21%moisture content maize to 15%moisture content at a cost of Can.$7.80/tonne for propane plus aeration costs to cool the grain.Procedures for safe storage of grain are outlined and the capabilities and planned use of a new grain storage research facility at the University of Manitoba are discussed.ó2003Elsevier Science Ltd.All rights reserved.

Keywords:Grain storage;Near-ambient drying;Hot air drying;Aeration systems;Insects

1.Introduction

On average,2.0Bt (billion tonnes)of grains,oilseeds,and legumes (hereafter referred to as grains)are pro-duced annually in the world (Statistical handbook,2000).The grains need to be stored safely until consumed.A stored grain bulk is a man-made ecological system in which deterioration of the stored product results from interactions among physical,chemical,and biological factors.The important factors are:temperature,mois-ture,carbon dioxide (CO 2),oxygen (O 2),grain charac-teristics,microorganisms,insects,mites,rodents,birds,geographical location,and granary structure (Jayas,1995).The storage life of grains depends mainly on two physical factors:temperature and moisture content (Fig.1).The survival and reproduction of biological agents in grain are dependent to a great extent on the temperature and moisture levels (White,1995).Stored-product insects can live at temperatures from 8to 41°C and inter-gran-ular relative humidities (r.h.)from 1%to 99%(Sinha &Watters,1985).Usually development and multiplication are optimum near 30°C and 50–70%r.h.(Howe,1965;

Sinha,1973a;Sinha &Watters,1985)but stop at 18°C (Fields &White,1997).Mites can live at temperatures from3to 41°C and relative humidities from 42%to 99%with the optimum for development and multiplication near 25°C and 70–90%r.h.Fungi can develop at tem-peratures from )2to 55°C and relative humidities from 70%to 90%with the optimum temperature near 30°C,and relative humidity around 80%.There is considerable variation in optimum conditions for di?erent species.Localized regions may occur in stored-grain bulks for optimum development and multiplication of insects,mites,and fungi even when the average conditions of the bulk would prevent pest infestation.

Mycotoxins are poisonous metabolites produced by certain fungal genera,which can infect crops both in the ?eld and in storage.Toxins produced by storage fungi in grain in Canada are sterigmatocystin,ochratoxin A,and citrinin.Several toxins are produced pre-harvest by Fusarium fungi (D.Abramson,personal communica-tion).Conditions favoring the development of mycotox-ins in cereals before and after harvest are not well-understood,but are of particular importance to grain-exporting countries concerned with maintaining high standards of quality in their produce.On-farm storage is common in the Canadian prairie region,and granary studies have shown the potential for mycotoxin formation in several stored cereal grains when they have high moisture contents (Abramson,Sinha,&Mills,1980,

*Corresponding author.Tel.:+1-204-474-6860;fax:+1-204-474-7568.

E-mail address:digvir_jayas@umanitoba.ca (D.S.Jayas).1

Address:Cereal Research Centre,Agriculture and Agri-Food Canada,195Dafoe Road,Winnipeg,MB,Canada R3T 2M9.

doi:10.1016/S0956-7135(03)00014-8

Food Control 14(2003)

255–261

https://www.wendangku.net/doc/5e18833298.html,/locate/foodcont

1983,1985,1990a,b,1999).Although many cause–e?ect relationships have yet to be investigated,some factors likely to a?ect mycotoxin formation are:moisture,tem-perature,time,invertebrate vectors,damage to the seed,O 2and CO 2levels,inoculumload,com position of sub-strate,fungal infection level,prevalence of toxigenic strains,and microbiological interactions (Abramson et al.,1999).It has been postulated that crop spoilage,fungal growth and mycotoxin formation result from the interaction of several of these factors in stored products (Abramson,1991;Frisvad,1995;Ominski,Marquardt,Sinha,&Abramson,1994;Wilson &Abramson,1992).An understanding of the factors involved would facilitate the prediction and prevention of mycotoxin development.Deterioration of grain and production of mycotoxins in grains can be reduced by properly drying grain to or below safe moisture contents (Table 1)and storing it at cool temperatures in properly designed storage struc-tures (Jayas,White,&Muir,1995).Mathematical models can be used to predict abiotic parameters such as

moisture content,inter-granular CO 2and grain tem-perature which can be correlated to changes in levels of biotic agents and mycotoxin production.This paper describes the structures commonly used for storage of grains in Canada,procedures needed to maintain the quality of grains and the role of mathematical models in managing stored-grain ecosystems.2.Canadian system

2.1.Brief description

Canada produces an average of 55Mt (million ton-nes)of grains annually (Statistical handbook,2000).About 70%of these grains are exported through a well-planned grain distribution system.Typically the pro-ducers store their grain on-farmin ?at-bottombins of about 100tonne capacity.These cylindrical bins are made by bolting sections of corrugated steel together (Fig.2).Although hopper-bottombins cost m ore than ?at-bottom bins per tonne of storage,many farmers are buying welded-steel hopper-bottombins (Fig.3)to store their grain.The main reasons for the purchase of hop-per-bottombins by the farm ers are:(i)the ease of grain handling,(ii)less exposure to grain dust during un-loading because no shoveling of grain is required,and (iii)perceived less spoilage in the hopper-bottombin.Westeel (a Division of Jannock Steel Fabricating Company),a major ?at-bin manufacturer in Manitoba,has started manufacturing a hopper-bottom for retro-?tting to corrugated-steel ?at-bottombins.

Farmers deliver their grain to primary elevators (grain handling facilities)using farmtrucks.The grain is graded by visual inspection or comparison with stan-dard samples or both.The standard samples are pre-pared every year by the Canadian Grain Commission to

Table 1

Upper limit of safe moisture contents a for storing grain up to a year under Canadian Prairie climatic conditions Crop

Moisture content b (%wb)Wheat 14.5Oats 14.0Barley 14.8Rye

14.0Flaxseed

10.0Canola and rapeseed 10.0Mustard seed 9.5Peas 16.0Lentils 14.0Fababeans 16.0Buckwheat 16.0Triticale 14.0Corn 15.5Soybeans

14.0Sun?ower seed 9.5Sa?ower seed

9.5

a Compiled from CGC (1993).

For long-termstorage (>1year)in well-engineered structures,the moisture content should be 1–3%points less than the values listed in this table.Depending on the climatic conditions of a region,values given in Table 1may need to be changed

considerably.

Fig.2.Corrugated steel,?at-bottombins at Cereal Research Centre Farm(28tonne

capacity).

Fig.1.Safe storage guidelines for canola (MDA,1987).

256 D.S.Jayas,N.D.G.White /Food Control 14(2003)255–261

re?ect the environmental conditions during harvest.Railway cars transport the grain fromprim ary elevators to terminal elevators (export elevators).The terminal elevators,clean,store and ship grain to export stan-dards.When needed,grain is typically dried on farms.2.2.Need for drying grains

It is not always possible to reduce the moisture con-tent of grains to safe levels in the ?eld because of many uncontrollable factors.In many countries,price of grains is high just before the harvest of new crops.By harvesting grains wet and removing moisture arti?cially,farmers or managers of cooperative farms (hereafter referred to as farmers)may increase their pro?ts.In other parts of the world where two or three crops are grown in a year,harvesting grains at high moisture re-duces the growing season (because the crop is not dried in the ?eld)for each crop and thus provides farmers more time for other in-?eld operations.Harvesting of ‘‘wet’’grains increases the harvest period allowing a longer use of harvesters on mechanized farms or of scarce manual labor used for harvesting in many parts of the world.Harvesting of ‘‘wet’’grains reduces shat-tering losses in the ?eld.In many years,frequent rains force farmers to harvest ‘‘wet’’grains.Therefore,arti-?cial removal of moisture from grains is a necessity on all farms (Pabis,Jayas,&Cenkowski,1998).Grain can be dried using air at near-ambient or high temperatures resulting in ‘‘near-ambient air’’or ‘‘hot air’’drying.2.3.Near-ambient drying system––a relatively slowbut lowcost technology

In a typical near-ambient system,the main compo-nents of the drying systemare:a bin to contain bulk

grains,a plenumwith a perforated area to introduce air through the grains,a fan to force air,and one or more roof vents to exhaust air (Fig.4).Air is forced through the bulk at 5to 40(L/s)/m 3of grain,depending on the moisture content,grain is dried in layers and distinct zones of dry,drying,and wet grain are created in the bulk (Fig.4).The con?guration of drying patterns and progress of drying depend on the type of grain being dried,initial moisture of the grain,condition and amount of air being forced through the grain,and the uniformity of air distribution within the grain bulk.A ?at-bottombin ?lled to a level surface and equipped with a fully perforated ?oor above a plenumprovides the most uniform air distribution through bulk grain.Many other con?gurations and size of bins are used for this purpose.Other con?gurations of air plenums are shown in Fig.5for ?at-bottombins,and in Fig.6for hopper-bottombins.In these system s (Figs.5and 6),the main direction of air movement through the grain is vertically up.Systems are also designed such that air travels mainly horizontally through grain (Fig.7a)or vertically downward through grain (Fig.7b).Other designs to introduce air into ?at and hopper-bot-tombins are continually being developed.Near-am bient drying can lower the moisture content of canola up to 2%over 2months after harvest (September–November)at a cost of Can.$0.87/tonne (the cost in 2002)(kilowatts of fan ?hours ?$0:055per kW h)(Sinha,Mills,Wallace,&Muir,1981).2.4.Hot air dryers

Dryers used for grain drying can be classi?ed based on:(i)?ow of grain (batch,recirculating,and continu-ous);(ii)relative motions of grain and drying air (con-current,counter-current,cross,and mixed ?ow);

and

Fig.3.Welded-steel hopper-bottombins at Glenlea Research Farm (56tonne capacity).

D.S.Jayas,N.D.G.White /Food Control 14(2003)255–261257

(iii)source of heat (solar,propane,and electrical).The relative motions of grain and drying air only occur in the continuous ?ow dryers.Either propane or electrical sources of heat can be used in all types of dryers.Therefore,various types of dryers used in the grain in-dustry can be placed into three groups:batch,recircu-lating,and continuous (Pabis et al.,1998).When using hot air for drying grain,grain should not be heated above the maximum allowed temperature for a partic-ular end use (Table 2).A typical example of the cost of drying maize from 21%to 15%using a propane batch drier is Can.$7.80/tonne (Personal communication,F.Helen,Oakbank,MB).The dried maize must then be rapidly cooled by aeration.

3.Procedures for safe storage of grains

Once grain is dry and cool and placed in a weather-proof and rodent-proof structure it can usually be stored for long periods without su?ering quality loss from fungal deterioration or insect feeding such as lowered germination,increased free fatty acids and other bio-chemical changes (Tipples,1995).However,if grain is stored in large bulks without aeration it will be indirectly a?ected by the weather.The bulk will retain the heat it had at harvest in the centre of the bulk (Jayas,Ala-gusundaram,Shunmugam,Muir,&White,1994)and re?ect external ambient temperatures near the periph-ery.In Canada,grain can remain warm (15–20°C)throughout the winter (outside temperatures can be as low as )20to )30°C)and air convection currents carry moisture to the top-centre of the bulk which can result in localized grain spoilage (Jayas,1995;Sinha,Yaciuk,&Muir,1973)and mycotoxin production (Abramson,1991).

Insects,mites,and fungi can rapidly increase in moist and warmgrain producing heat,m oisture,and CO 2

Table 2

Maximum safe temperature (°C)of heated air entering grain for drying for various end uses (Hall,1980)Crop

End use Seed

Commercial use a Animal feed a Ear corn 4354

82Shelled corn 435482Wheat 436082Oats 436082Barley 414182Sorghum436082

Soybeans 4349Rice 4343Peanuts 32

Higher air temperatures than those listed may be used when the grain is dried under carefully controlled conditions so that the maxi-mum temperature of the kernels,at any time,does not exceed those listed in the

table.

respiration(White&Sinha,1980).Speci?c climatic conditions determine which form of spoilage is most likely to occur(Sinha,1973b)with mites predominating in temperate climates,fungi in tropical humid or sub-tropical humid climates and insects in dry,hot climates.

The practicality of aeration cannot be overstated because grain is often harvested hot[up to8°C warmer than ambient air temperature at harvest(Prasad,Muir, &Wallace,1978)]and wet.In one Canadian study wheat and barley stored in550-tonne capacity bins were monitored for each of12annual storage cycles(White et al.,1999).There were two3-horse-power(2.25kW) fans per bin with5%of the?oor area perforated steel with a corresponding air plenum.Grain was typically harvested near34°C but with continuous aeration was <20°C within2weeks so insects and fungi were rarely a problemand fan operation varied from221h in one year to678h in the wettest year.In the wettest2years pockets of molding grain occurred near the?oors and after1year of storage0.7ppmochratoxin A occurred in wheat and5.2ppmcitrinin,2.2ppmochratoxin A,and traces of sterigmatocystin were found in the mouldy barley.The moulded grain was discarded.

Good storage practices have been outlined by White (2000)and include the following procedures:?Prepare the bin,before storing the new crop:sweep or vacuumthe?oor and walls;burn or bury sweepings that contain spoiled or infested grain;seal cracks to keep out?ying insects fromoutside,rain,and snow;

and spray the walls and?oors with a recommended insecticide.

?Install an aeration systemto reduce tem perature gra-dients and moisture condensation.

?Dry tough or damp crops soon after harvest as they are more likely to heat and become infested with in-sects and mites than dry(straight-grade)crops;then cool after drying.

?Examine stored crops every2weeks for signs of heat-ing or infestation;either check temperatures,carbon dioxide levels,and insect activity by traps,or probe and screen samples.

?Move heated or infested crops into another bin if out-door temperatures are su?ciently cold to break up hot-spots and control infestation.

?Check the top of binned crops and remove snow, if present,before a crust of mold develops.

?If an insect infestation occurs and aeration is not available,seal the bin and fumigate the grain with phosphine gas.

4.Role of mathematical models

Experimental studies can be conducted to measure changes in temperature,moisture content,and gas con-centration in stored grain.But the large number of biotic and abiotic factors and their inter-relationships in stored-grain ecosystems makes full-scale experimental studies expensive and time consuming,and the generalizations needed to predict the variables accurately are di?cult to make.Mathematical models,if based on the principles of physical and biological sciences and properly validated, can be used to study the e?ect of various parameters such as weather,grain condition,and size,shape,and material of the storage structure on the distribution of tempera-ture,moisture,and gases(Jayas et al.,1994).The major advantages of validated models are their ability to answer ‘‘what if?’’questions and their transferability to di?erent climatic regions of the world.If economic and social considerations are suitable this transferability can make the models globally rather than locally applicable as is expected of experimental studies(Jayas,1995).

5.Grain storage research facility

A facility has been built at the University of Mani-toba to conduct research on all aspects of grain storage (Fig.8).Examples of potential collaborative research projects between engineers in the Department of Bio-systems Engineering at the University of Manitoba and scientists at the Cereal Research Centre of Agriculture and Agri-Food Canada

are:

Fig.8.Grain storage research facility at the University of Manitoba.

D.S.Jayas,N.D.G.White/Food Control14(2003)255–261259

(a)to optimize computer control strategies for drying

and aerating grains,oilseeds,and new crops as they become important,such as beans,lentils,and peas;

(b)to develop automatic controls for fans for near-

ambient drying and aeration;

(c)to evaluate existing and design new systems to in-

troduce air into the grain for drying and aeration in hopper-bottombins;

(d)to determine air conditions and combinations of

methods for drying new crops without detrimental e?ects on end-use quality;

(e)to design and evaluate new sensors and automatic

controls for high temperature dryers;

(f)to design and develop new,economically feasible,

drying systems(e.g.,infrared and microwave dry-ing);

(g)to design and evaluate cleaning equipment and ma-

terial handling systems for specialty crops to ensure quality is preserved;

(h)to develop new cleaning and handling systems that

minimize seed loss during cleaning and handling;

(i)to develop systems to automatically sample,ana-

lyze using machine vision technology,and adjust cleaning and handling machines to maximize clea-ner throughput while meeting pre-established clean-ing tolerances;

(j)to develop the potential of machine vision technol-ogy to assist grain inspectors in grain grading and in detecting insect infestations and fungal damage; (k)to design systems to kill insects in grain using car-bon dioxide;

(l)to design systems to kill insects using high temper-atures without detrimental e?ects on grain quality; (m)to develop aeration strategies to use Canadian cold ambient-temperatures for controlling insects; (n)to develop integrated pest management(IPM)strat-egies;

(o)to develop new grain transport logistics(e.g.,con-tainerized shipping or compacted?our);

(p)to design and develop new equipment for dehulling pulses;

(q)to measure physical properties,sorption and de-sorption isotherms,and thermal properties of grain; (r)to determine storability of new crops,crop products, new cultivars of established crops,and animal feeds; (s)to develop processing technologies that uniformly mix medicinal and nutritional components into feed;and

(t)other projects of interest to the Canadian and world grain industry.

Acknowledgements

The funding to build the Grain Storage Research Facility were provided by the Canada Foundation for Innovation,Manitoba Innovation Fund,Western Eco-nomic Diversi?cation,Manitoba Hydro,Agriculture and Agri-Food Canada,industry and private donors, and the University of Manitoba.Research funds are usually provided by Natural Sciences and Engineering Research Council of Canada,Canada Research Chair Program,industry,and Manitoba Government. References

Abramson,D.(1991).Development of molds,mycotoxins and odors in moist cereals during storage.In J.Chelkowski(Ed.),Cereal grain:Mycotoxins,fungi and quality in drying and storage(pp.119–147).Amsterdam:Elsevier.

Abramson, D.,Mills,J.T.,&Sinha,R.N.(1990a).Mycotoxin production in amber durum wheat stored at15and19%moisture content.Food Additives and Contaminants,7,617–628. Abramson,D.,Sinha,R.N.,&Mills,J.T.(1980).Mycotoxin and odor formation in moist cereal grain during granary storage.Cereal Chemistry,57,346–351.

Abramson,D.,Sinha,R.N.,&Mills,J.T.(1983).Mycotoxin and odor formation in barley stored at16and20%moisture in Manitoba.Cereal Chemistry,60,350–355.

Abramson, D.,Sinha,R.N.,&Mills,J.T.(1985).Mycotoxin formation and quality changes in granary-stored corn at16and 21%moisture content.Sciences des Aliments,5,653–663. Abramson, D.,Sinha,R.N.,&Mills,J.T.(1990b).Mycotoxin formation in HY-320wheat during granary storage at15and19% moisture content.Mycopathologia,111,181–189.

Abramson, D.,Hulasare,R.,White,N. D.G.,Jayas, D.S.,& Marquardt,R.R.(1999).Mycotoxin formation in hulless barley during granary storage at15and19%moisture content.Journal Stored Products Research,35,297–305.

Anonymous,2000.Statistical handbook.Winnipeg,MB:Canada Grains Council.

CGC(1993).Grain grading handbook for Western Canada.Winnipeg, MB:Canadian Grain Commission.

Hall,C.W.(1980).Drying and storage of agricultural crops.West port, CT:AVI.

Fields,P.G.,&White,N.D.G.(1997).Survival and multiplication of stored-product beetles at simulated and actual winter temperatures.

Canadian Entomologist,129,887–898.

Frisvad,J.C.(1995).Mycotoxins and mycotoxigenic fungi in storage.

In D.S.Jayas,N.D.G.White,&W.E.Muir(Eds.),Stored-grain ecosystems(pp.251–288).New York,NY:Marcel Dekker. Howe,R.W.(1965).A summary of estimates of optimal and minimal conditions for population increase of some stored products insects.

Journal of Stored Products Research,1,177–184.

Jayas,D.S.(1995).Mathematical modeling of heat,moisture,and gas transfer in stored-grain ecosystems.In D.S.Jayas,N.D.G.White, &W.E.Muir(Eds.),Stored-grain ecosystems(pp.527–567).New York,NY:Marcel Dekker.

Jayas,D.S.,Alagusundaram,K.,Shunmugam,G.,Muir,W.E.,& White,N.D.G.(1994).Simulated temperatures of stored grain bulks.Canadian Agricultural Engineering,36(4),239–245. Jayas,D.S.,White,N.D.G.,&Muir,W.E.(Eds.).(1995).Stored-grain ecosystems(p.757).New York,NY:Marcel Dekker.

MDA(1987).Grain aeration and unheated air drying.Publication No.

Agdex732-1.Manitoba Department of Agriculture,Winnipeg,MB. Ominski,K.H.,Marquardt,R.R.,Sinha,R.N.,&Abramson,D.

(1994).Ecological aspects of growth and mycotoxin production by storage fungi.In https://www.wendangku.net/doc/5e18833298.html,ler,&H.L.Trenholm(Eds.), Mycotoxins in grain(pp.287–312).St Paul,MN:Eagan Press.

260 D.S.Jayas,N.D.G.White/Food Control14(2003)255–261

Pabis,S.,Jayas,D.S.,&Cenkowski,S.(1998).Grain drying:Theory and practice.New York,NY:John Wiley,303p.

Prasad,D.C.,Muir,W.E.,&Wallace,H.A.H.(1978).Characteristics of freshly harvested wheat and rapeseed.Transactions of the American Society of Agricultural Engineers,21,782–784.

Sinha,R.N.(1973a).Interrelations of physical,chemical,and biological variables in the deterioration of stored grains.In R.N.

Sinha,&W.E.Muir(Eds.),Grain storage:Part of a system(pp.

15–47).Westport,CT:AVI Pub.Co.,Inc.

Sinha,R.N.(1973b).Ecology of storage.Annals de Technologie Agricole,22,351–369.

Sinha,R.N.,Mills,J.T.,Wallace,H.A.H.,&Muir,W.E.(1981).

Quality assessment of rapeseed stored in ventilated and non-ventilated farmbins.Sciences des Aliments,1,247–263.

Sinha,R.N.,&Watters, F.L.(1985).Insect pests of?our mills,grain elevators,and feed mills and their control.Publica-tion1776.Research Branch,Agriculture Canada,Ottawa,Ont.

290p.

Sinha,R.N.,Yaciuk,G.,&Muir,W.E.(1973).Climate in relation to deterioration of stored grain.A multivariate study.Oecologia,12, 69–88.

Tipples,K.H.(1995).Quality and nutritional changes in stored grain.In D.S.Jayas,N.D.G.White,&W.E.Muir(Eds.),Stored-

grain ecosystems(pp.325–351).New York,NY:Marcel Dekker, 757p.

White,N.D.G.(1995).Insects,mites,and insecticides in stored-grain ecosystems.In D.S.Jayas,N.D.G.White,&W.E.Muir(Eds.), Stored-grain ecosystems(pp.123–167).New York,NY:Marcel Dekker.

White,N. D.G.(Ed.).(2000).Protection of farm-stored grains, oilseeds,and pulses from insects,mites and molds.Cereal Research Centre,Agriculture and Agri-Food Canada,http://res2.agr.ca/ winnipeg/cgs_e.htm.

White,N.D.G.,&Sinha,R.N.(1980).Changes in stored-wheat ecosystems infested with two combinations of insect species.

Canadian Journal of Zoology,58,1524–1534.

White,N. D.G.,Demianyk, C.J.,Sinha,R.N.,Mills,J.T., Abramson,D.,Muir,W.E.,&Jayas,D.S.(1999).Multi-year monitoring for quality changes of grain stored in550tonne capacity grain bins in western Canada.Proceedings of the7th international working conference on stored-product protection:Vol.2 (pp.1301–1313).Chengdu,PR China:Sichuan Publishing House of Science and Technology.

Wilson,D.M.,&Abramson,D.(1992).Mycotoxins.In D.B.Sauer (Ed.),Storage of cereal grains and their products(pp.341–391).

St Paul,MN:American Association of Cereal Chemists.

D.S.Jayas,N.D.G.White/Food Control14(2003)255–261261