production of grainin the world is arounda billion tonnes.The damage during
storageof grainin the developing countries is between 5% and 40%depending on
the periodof storage.Besidesspoilageof the commoditiesbecauseof the
metabolismof insects and microflora,oxygenis consumedand heat,waterand
carbon dioxideare released.Thisbiological process causesthe formation of hot
spots in the grainbulk,withtemperaturethat risesup to 60 ÎC. The continuation
of the biological heating is the chemical heating that is caused by the oxidation of
unsaturatedfats. In this process the heat produced can reachup to 300 ÎC and the
commoditiesignite. It shouldalso be mentionedthat someinsects are ableto
survive withmoisturecontentof the grainas low as 1.0%.Therefore, the hygiene
managementof dry storedproducts is of utmostimportancefor safe storage.
26.2 The grainbulkas an ecosystem...
The grainbulkis regardedas a dynamicsystem. Seedsare livingmatter but in a
state of dormancy and theiractivity is verylow.Thissituation is the best for
storage: the deeperthe dormancy of the seeds, the better.To understandthe
ecology of storageone shouldconsider a grainbulkas an ecosystem(Fig. 26.1).
The grain bulk ecosystem consists of biotic and abiotic factors, and the
environmental factorsof temperature, atmosphericgasesand moisture.
26.2.1 Bioticfactors
Biotic factorsare the live components,and consist of:
∑ grain;
∑ insects and mites,damaging components;
∑ microflora= (fungi,bacteriaand yeast),also damagingcomponent.
These will be dealtwithlater.
26.2.2 Abioticfactors
Abiotic factors are inanimate,and consistof:
∑ dustand foreignmaterial;
∑ intergranularair;
∑ watervapour;
∑ storagestructure.
Dust, dockage and foreignmaterial
These are goodsubstratesfor insectand fungidevelopment.
Intergranular air (space)
The intergranular air is the air between the seedsor othercommodities. It
occupies 20±50% of the volumeof the bulkgrain.The intergranularair is
importantfor the following reasons:
408 Handbookof hygiene controlin the foodindustry