TECHNOLOGY OF CEREALS TABLE 5. 4 Alphabetical List of Most Important Secondary Insect Pests Common Name Anagasta kuehniella Zella* mediterranean flour moth Phycidae Almond moth Flour mill beetle hestia elutella huhne Oryzaephilus surinamensis L ephilus mercator Auv Merchant grain beetle Tenebriodes mauritanicus l ranidae teum Herbst Red flour beetle conidae Triboliumconfusum Duval Confused flour beetle Formerly Ephestia kuehniella. emerges. The larva is the form most damaging The time taken for development of both insects to the stored crop as it feeds voraciously. In and mites is influenced by temperature, the consequence it grows rapidly, passing through a greater the temperature the more rapid the deve series of moults during which its soft cuticle is lopment up to the maximum tolerated by the shed, thus facilitating further growth. Finally species pupation occurs; the pupa, chrysalis or cocoon The primary pests- those attacking whole does not eat and appears inactive. However, grains -are given in Table 5.3 changes continue and the final metamorphosis The three most damaging of these pests in the leads to the emergence of the adult form. The U. K. are shown in Fig. 5. 4. life cycle of mites is simpler as eggs hatch into The most important secondary insect pests nymphs which resemble the adult form, although those feeding only on damaged or previously there are only six legs present at this stage. By a attacked grains - are given in Table 5.4 series of four moults the adult form is achieved The saw-toothed grain beetle is shown in Fig. 5.5 Saw-toothed grain beetle, Crown Copyright. Central Science ratory 1993
108 TECHNOLOGY OF CEREALS TABLE 5.4 Alphabetical List of Most Important Secondary Insect Pests Systematic Name Common Name Family Anagasta kuehniella Zella* Mediterranean flour moth Phycitidae Gadra cautella Walker Almond moth " Cyptolestes pusillus Schonherr Flat grain beetle Cucu jidae Cyptolestes turacus Grouv Flour mill beetle " Ephestia elutella Hubner Tobacco moth Phycitidae Oyzaephilus surinamensis L. Saw-toothed grain beetle Cucujidea Oryzaephilus mercator Fauv. Plodia interpunctella Hubner Indian meal moth Phycitidae Tenebriodes mauritanicus L. Cadelle Ostomatidae Tribolium castaneum Herbst. Red flour beetle Tenebrionidae Tribolium confusum Duval Trogodenna granarium Everto Khapra beetle Dermestidae Merchant grain beetle " Confused flour beetle " * Formerly Ephestia kuehniella. FIG 5.5 Oryzaephilus Laboratory 1993. 108 TECHNOLOGY OF CEREALS TABLE 5.4 Alphabetical List of Most Important Secondary Insect Pests emerges. The larva is the form most damaging to the stored crop as it feeds voraciously. In consequence it grows rapidly, passing through a series of moults during which its soft cuticle is shed, thus facilitating further growth. Finally pupation occurs; the pupa, chrysalis or cocoon does not eat and appears inactive. However , changes continue and the final metamorphosis leads to the emergence of the adult form. The life cycle of mites is simpler as eggs hatch into nymphs which resemble the adult form, although there are only six legs present at this stage. By a series of four moults the adult form is achieved. The time taken for development of both insects and mites is influenced by temperature, the greater the temperature the more rapid the development up to the maximum tolerated by the species. The primary pests -those attacking whole grains- are given in Table 5.3. The three most damaging of these pests in the U.K. are shown in Fig. 5.4. The most important secondary insect pests ~ those feeding only on damaged or previously attacked grains -are given in Table 5.4. The saw-toothed grain beetle is shown in Fig. 5.5. FiG 5.5 Oryzaephilus surinamensis. Saw-toothed grain beetle. Crown Copyright. Central Science Laboratory 1993
STORAGE AND PRE-PROCESSING FiG 5. X-ray phot of wheat grains, two uninfested (bottom leff), the others showing cavities n. an insect is visible within one of the cavities. (Part of a picture in Photograph. Sci., 1954, 2: 113; reproduced by courtesy of Prof. G. A. G. Mitchell and the Editor fournal of Photographic Science. Those insects listed in the tables are considered even though only a hollow bran coat may remain major pests. They are particularly well adapted Detection by means of soft X-rays is possible to life in the grain bin and are responsible for (Fig. 5.6) most of the insect damage to stored grain and cereal products. Minor pests occur mainly in Damage caused by insects and mites stores in which grain has started to deteriorate due to other causes, while incidental pests include Serious grain losses due to consumption of those that arrive by chance and need not even be grain by insects and mites occurs only after able to feed on grains. For further information prolonged storage under suitably warm conditions on minor and incidental insect pests specialist They are most serious in hot climates. Other works such as Christensen(1974)should be problems caused by insects include creation of hot- consulted spots around insect populations where metabolic Among the major primary pests five species activity leads to local heating Moisture move- develop inside grains. Weevils (grain, rice and ments and condensation in cooler areas results in maize) lay eggs inside while lesser grain borers caking, and encourages fungal infestation(see and Angoumois grain moths deposit eggs outside Fig 5.1) but their newly hatched larvae promptly tunnel Introduction of insects and mites from wheat into grains. The presence of the insect and the stores to flour mills can cause serious deteriora- damage it causes may not be evident from outside tion in the products. Mite excreta taints flour with
STORAGE AND PRE-PROCESSING 109 FiG 5.6 X-ray photograph of wheat grains, two uninfested (bottom left), the others showing cavities caused by insect infestation. An insect is visible within one of the cavities. (Part of a picture in J . Photograph. Sci., 1954, 2: 113; reproduced by counesy of Prof. G. A. G. Mitchell and the Editor of Journal of Photographic Science.) even though only a hollow bran coat may remain. Detection by means of soft X-rays is possible (Fig. 5.6). Those insects listed in the tables are considered major pests. They are particularly well adapted to life in the grain bin and are responsible for most of the insect damage to stored grain and cereal products. Minor pests occur mainly in stores in which grain has started to deteriorate due to other causes, while incidental pests include those that arrive by chance and need not even be able to feed on grains. For further information on minor and incidental insect pests specialist works such as Christensen (1974) should be consulted. Among the major primary pests five species develop inside grains. Weevils (grain, rice and maize) lay eggs inside while lesser grain borers and Angoumois grain moths deposit eggs outside but their newly hatched larvae promptly tunnel into grains. The presence of the insect and the damage it causes may not be evident from outside Damage caused by insects and mites Serious grain losses due to consumption of grain by insects and mites occurs only after prolonged storage under suitably warm conditions. They are most serious in hot climates. Other problems caused by insects include creation ofhotspots around insect populations where metabolic activity leads to local heating. Moisture movements and condensation in cooler areas results in caking, and encourages fungal infestation (see Fig. 5.1). Introduction of insects and mites from wheat stores to flour mills can cause serious deterioration in the products. Mite excreta taints flour with
110 TECHNOLOGY OF CEREALS a minty smell and hairs from the animals bodies however, have several advantageous features can cause skin and lung disorders in workers Thus underground stores provide protection from handling infected flour. Silk from the larvae of temperature fluctuations, the most successful the Mediterranean four moth webs together simple ones being found in hot dry regions. They causing agglomeration of grains and blockages in are filled, to leave little air space, and sealed , to handling and processing equipment. In tropical approach the concept of hermetic storage under countries termites can weaken the structure of a which insects and moulds rapidly use up oxygen store, leading to its collapse giving rise to high CO2 content of the intergrain atmosphere. In more humid regions ventilation Vertebrate pests is de ble as the crop may have to be stored before reaching a safe moisture level. Such a The principal vertebrate pests in cereal stores system is suited to cob maize rather than threshed are rodents and birds. In many countries the three grains, as adequate space for air movement within main rodent species involved are: the store is essential. Clearly the requirements Rattus norvegicus -the Norway, common of ventilation and exclusion of insects are not immediately compatible and hence careful design Ratus rattus is essential Mus musculus the roof, ships or black rat; Storage of maize as cobs is practised now largely by small scale growers producing for the apart from consuming grains, particularly the requirements of the local community. It was at embryo of maize, rodents cause spoilage through one time adopted more widely even in highly their excretions which contain micro-organisms commercial practice, much as small grain cereals pathogenic to man. These include salmonellosis, were stored unthrashed in ricks murine typhus, rat-bite fever and Weils disease In the commercial context stores are needed Rodents also damage stores'structural elements, for three purposes containers, water pipes and electric cables In well-managed stores access by rodents 1. Holding stocks on the farm prior to sa denied and good housekeeping practice, such 2. Centralization before distribution or processing as removal of grain spillages, maintenance of during the year following harve uncluttered surroundings and regular inspec- 3. Storage of annual surpluses over a longer tions, prevent problems. The same is true of birds. These are serious pests only when access Farm stores may consist of any available space is easy, as for example in hot countries where that will keep out the elements. The facilities for grain may be left to dry in the sun. Damage to protection against mould and pests are very drains and blockage of pipes by nests can variable Stores range from small wooden enclos give rise to secondary storage problems through ures in the barn, to round steel bins holding 25- promoting local dampness in some stores 80 tonnes, to silos of larger capacities. Good on farm storage facilities allow farmers to choose the Design of storage facilities time to sell, to receive the best prices The degree of centralization depends upon the The requirements of long term safe storage are marketing regime within the country of produc protection against dampness caused by weather tion. In North America, Country elevators and or other sources, micro-organisms, destructively Terminal elevators with storage capacity up to high temperature, insects, rodents and birds, 500,000 tonnes exist. The country elevators provide objectionable odours and contaminants and un- a local staging en route to terminal elevators which authorized disturbance. Clearly the simplest stores include high-capacity equipment for cleaning such as piles on the ground, unprotected are suit- drying and conditioning of grain. The term able for short periods only. Other simple stores, 'elevator'is applied to the entire facility although
110 TECHNOLOGY OF CEREALS a minty smell and hairs from the animals’ bodies however, have several advantageous features. can cause skin and lung disorders in workers Thus underground stores provide protection from handling infected flour. Silk from the larvae of temperature fluctuations, the most successful the Mediterranean flour moth webs together simple ones being found in hot dry regions. They causing agglomeration of grains and blockages in are filled, to leave little air space, and sealed, to handling and processing equipment. In tropical approach the concept of hermetic storage under countries termites can weaken the structure of a which insects and moulds rapidly use up oxygen, store, leading to its collapse. giving rise to high C02 content of the intergrain atmosphere. In more humid regions ventilation is desirable as the crop may have to be stored before reaching a safe moisture level. Such a Vertebrate pests The principal vertebrate pests in cereal stores system is suited to cob maize rather than threshed are rodents and birds. In many countries the three grains, as adequate space for air movement within main rodent species involved are: the store is essential. Clearly the requirements of ventilation and exclusion of insects are not immediately compatible and hence careful design Rattus nomegzcus - the Norway, common or brown rat; is essential. Rattus rattus -the roof, ships or black rat; Storage of maize as cobs is practised now largely by small scale growers producing for the Mus musculus - the house mouse. Apart from consuming grains, particularly the requirements of the local community. It was at embryo of maize, rodents cause spoilage through one time adopted more widely even in highly their excretions which contain micro-organisms commercial practice, much as small grain cereals pathogenic to man. These include salmonellosis, were stored unthrashed in ricks. murine typhus, rat-bite fever and Weil’s disease. In the commercial context stores are needed Rodents also damage stores’ structural elements, for three purposes: 1. Holding stocks on the farm prior to sale. containers, water pipes and electric cables. 2. Centralization before distribution or processing In well-managed stores access by rodents is denied and good housekeeping practice, such during the year following harvest. as removal of grain spillages, maintenance of 3. Storage of annual surpluses over a longer uncluttered surroundings and regular inspec- period. tions, prevent problems. The same is true of birds. These are serious pests only when access Farm stores may consist of any available space is easy, as for example in hot countries where that will keep out the elements. The facilities for grain may be left to dry in the sun. Damage to protection against mould and pests are very drains and blockage of pipes by nests can variable. Stores range from small wooden enclosgive rise to secondary storage problems through ures in the barn, to round steel bins holding 25- promoting local dampness in some stores. 80 tonnes, to silos of larger capacities. Good onfarm storage facilities allow farmers to choose the time to sell, to receive the best prices. The degree of centralization depends upon the Design of storage facilities The requirements of long term safe storage are marketing regime within the country of producprotection against dampness caused by weather tion. In North America, Country elevators and or other sources, micro-organisms, destructively Terminal elevators with storage capacity up to high temperature, insects, rodents and birds, 500,000 tonnes exist. The country elevators provide objectionable odours and contaminants and un- a local staging en route to terminal elevators which authorized disturbance. Clearly the simplest stores include high-capacity equipment for cleaning, such as piles on the ground, unprotected, are suit- drying and conditioning of grain. The term able for short periods only. Other simple stores, ‘elevator’ is applied to the entire facility although
STORAGE AND PRE-PROCESSING 111 it refers literally to the mechanism(normally belt Settling is a continuous process arising in part and bucket) by which grains are raised to a from the collapse of hulls, brush hairs, embryo level from which they can be deposited into the tips etc large capacity silos invariably found on the Elevators are associated with good transport Control of pests and spoilage of grains facilities by road, rail, water or all three. Many are capable of loading grain into vessels at a rate A It is sometimes necessary to provide storage taken to ensure that the grain is in a suitable raIn e normal capacit of an condition for storing Criteria for the latter include elevator facility or elsewhere. In such conditions a suitably low moisture content, a low mould a relatively inexpensive expedient is the flat store. count and freedom from insects. Wheat contain- This is little more than a cover for a pile of dry ing live insects can be sterilized by passage grain adopting its natural form as poured Such through an entoleter(fig. 5.7), run at about 1450 a form is described by the angle of repose In the rev/min (BP 965267 recommends speeds of 3500 case of wheat the angle is 27 to the horizontal, rev/min for conditioned wheat, 1700 rev/min for hence fat stores have roofs close to this angle. dry wheat. Hollow grains and insects may be Very temporary stores may make use of inflatable broken up and can be removed by subsequent aspiration Flat stores are easy to fill but, as they have flat floors, removal of stocks is more difficult, usually requiring the use of mechanical shovels In con trast, silos usually have a floor formed like a conical hopper whose walls make an angle greater than 27 to the horizontal. Piles created by grains falling freely from a central spout are not uniform as whole grains tend to roll from the apex down the sloping surfaces. Small impurities and broken grains roll less readily and thus become trapped in the central core of the pile. Such a core is described as the spoutline. As the interstices can amount to 30% of the spoutline can reach that level. Because air irculation and hence heat loss is prevented, the spoutline can be associated with early deterioration through overheating. The diameter of the spoutline is proportional to the width of the bin Also in contrast to tall tower -like stores fat stores require little strength in the side walls. In a silo much of the pressure of the column of grain is borne not by the floor but by the side walls This is because each grain rests on several grains below it so that some of the weight is distributed laterally until it reaches the walls and, by friction and tiswunrGaceordingteche eereul ype. W,heara FiG5.7 Diagrammatic section through an En rests on them. In all stores some settling occurs ey:2.3 impeller: scnu is relatively dense and settling may be only 6% taken by air. (Reproduced from Milling, 1969 of volume but oats may pack as much as 28%
STORAGE AND PRE-PROCESSING 111 Settling is a continuous process arising in part from the collapse of hulls, brush hairs, embryo tips etc. Control of pests and spoilage of grains in store Deterioration in store is less likely if care is taken to ensure that the grain is in a suitable condition for storing. Criteria for the latter include a suitably low moisture content, a low mould count and freedom from insects. Wheat containing live insects can be sterilized by passage through an entoleter (Fig. 5.7), run at about 1450 rev/min. (BP 965267 recommends speeds of 3500 rev/min for conditioned wheat, 1700 rev/min for dry wheat.) Hollow grains and insects may be broken up and can be removed by subsequent it refers literally to the mechanism (normally belt and bucket) by which grains are raised to a level from which they can be deposited into the large capacity silos invariably found on the sites. Elevators are associated with good transport facilities by road, rail, water or all three. Many are capable of loading grain into vessels at a rate of 2,750 t/h. It is sometimes necessary to provide storage for grain beyond the normal capacity of an elevator facility or elsewhere. In such conditions a relatively inexpensive expedient is the flat store. This is little more than a cover for a pile of dry grain adopting its natural form as poured. Such a form is described by the angle of repose. In the case of wheat the angle is 27" to the horizontal, hence flat stores have roofs close to this angle. Very temporary stores may make use of inflatable covers. aspiration. Flat stores are easy to fill but, as they have flat floors, removal of stocks is more difficult, usually requiring the use of mechanical shovels. In contrast, silos usually have a floor formed like a conical hopper whose walls make an angle greater than 27" to the horizontal. Piles created by grains falling freely from a central spout are not uniform as whole grains tend to roll from the apex down the sloping surfaces. Small impurities and broken grains roll less readily and thus become trapped in the central core of the pile. Such a core is described as the spoutline. As the interstices can amount to 30% of the occupied space, fines in the spoutline can reach that level. Because air circulation and hence heat loss is prevented, the spoutline can be associated with early deterioration through overheating. The diameter of the spoutline is proportional to the width of the bin. Also in contrast to tall tower-like stores, flat stores require little strength in the side walls. In a silo much of the pressure of the column of grain is borne not by the floor but by the side walls. This is because each grain rests on several grains below it so that some of the weight is distributed laterally until it reaches the walls and, by friction, rests on them. In all stores some settling occurs ~~~~~~~~~~~~~~~ff~~~~~~~~~~. R+M is re1ative1y dense and sett1ing may be Only 6oh of volume but oats may pack as much as 28%. FIG 5.7 Diagrammatic section through an Entoleter Aspirator. 1, fixh ide~; 2, 3, e; 4< swkg mm; -5< .ph discharge over 6, cone; 7, valve controlling air flow. Arrows indicate path taken by air. (Reproduced from Milling, 1969, Oct 10, by courtesy of the Editor.)