10 Drying, Handling, and Storage of Raw Commodities

10 Drying, Handling, and Storage of Raw Commodities Carol Jones Mark Casada Otto Loewer The goal of postharvest grain drying, handling, and End-use quality storage operations is to preserve the harvest quality The definition of grain quality varies depending on of the grain and to add value by removing impuri- the intended end-use of the grain. For hard wheat, ties and identifying and segregating lots with special the ultimate criteria may be loaf volume for baked characteristics when appropriate. For agricultural bread; for soft wheat, the objective may be cookie products, quality loss may occur due to poor drying spread. Soybeans are processed for protein and oil techniques, improper handling, or lack of proper content. Corn has many uses and applications. For storage environments resulting in deterioration the ethanol industry, the amount of starch available from cracking, splitting, mold growth, insect dam- for fermentation is a critical quality factor. Ethanol age, sprouting, loss of germination, or dry matter producers may have other quality concerns because loss from respiration. Large grains such as corn — they sell co-products such as dried distillers grains especially when dried at high temperatures — are (DDGS) with minimal or no mycotoxin content; particularly susceptible to physical damage during mycotoxins are more concentrated in the distillers handling. Physical damage also makes grain more grains than in the incoming corn (Bennett and Rich- susceptible to invasion by storage fungi and insects. ard, 1996; Murthy et al., 2005). Grain Quality Milling is an important processing step for many grain products, so milling characteristics are often Characteristics important quality parameters for hard, soft, and durum wheat; corn; and rice. Specialized end- All postharvest operations attempt to maintain the uses may focus on one grain quality parameter, for initial quality of the harvested grain. During storage, example, high oil content in corn and soybeans to grain must be protected from deterioration or attack provide energy and amino acids in livestock and by molds, insects, rodents, and birds. Drying and poultry diets. handling operations must prevent physical or chemi- cal deterioration. The physical protection provided Grain grading by modern grain storage structures should eliminate serious bird and rodent damage. Molds and insects Originally, U.S. grain grading standards did not cannot be physically excluded from grain with cur- focus on product quality characteristics of inter- rent storage designs. They can be controlled through est in today’s specialty grains markets. Early grain grain temperature and moisture management. standards were developed to facilitate trade, describe physical properties and storability of the grain, and characterize product yield and grain quality. Initial grading standards addressed deterioration issues that Stored Product Protection 1 Part II | Management: Prevention Methods adversely affect product quality. Over the years stan- vention is needed to minimize product damage and dards have changed as rapid measurement technolo- loss of market value. gies have been developed that emphasize product quality characteristics. Influences Some standards relate to specific product quality The main reasons for grain quality decline are under issues. For example, insect damaged kernels (IDK), drying (storing grain with unsafe moisture and tem- addressed in Federal Grain Inspection Service perature levels), overdrying, grain respiration, insect (FGIS) wheat standards, pertain to potential mill- and rodent damage, and mold or other bacterial ing problems of insect fragments in the flour. FGIS contamination (Kazazis, 1980; Wilcke et al., 2000). added tests to address characteristics of interest to Proper grain moisture and temperature management buyers such as protein content of wheat and oil and is essential for reducing damage to the stored crop. protein content of soybeans. High humidity and temperature conditions promote insect infestation and mold development. Generally, Sampling the drier the grain in storage, the higher the storage temperature can be before mold begins to form. Quality measurement, or grading, of a grain sample Each grain or seed variety has its own safe storage assumes that the sample is representative of the moisture and temperature, and equilibrium relative quality of the lot sampled. A representative sample is humidity (ERH) criteria. critical. Without it, the grade assigned is meaning- less. The FGIS recommends continuous diverter- Drying damage type samplers for the most representative samples. The agency requires the use of specific grain probes: Overdrying grain causes cracking, darkening, and a grain trier, which is a gravity fill probe, and a seed damage. Although drying damage is often vacuum probe. The probe must be long enough to associated with corn, oilseeds such as soybeans, rape, reach the bottom of the truck or other container. The and canola also can be damaged when overdried. sample must be collected using an approved probing Seeds shatter during handling when dried to less pattern. Explicit probing patterns require up to nine than 6% moisture. Drying can cause damage that is probe locations on shallow flat-bottom trucks. More not visible. For example, overheated wheat may look probe locations are required for grain on barges normal, but contain denatured protein that affects (USDA-GIPSA, 1995). performance in making flour. Reducing heat levels during drying will minimize or prevent drying stress Nonofficial sampling in the grain industry often damage. involves using two or more probes to obtain a useful sample quickly. There is not as much assurance that Handling damage such a sample is representative. For nonofficial sampling, simulating a diverter-type sampler by crosscut- Mechanical handling can damage grain and seeds, ting a stream of flowing grain is recommended (Hel- reducing quality and encouraging other unfavorable- levang et al., 1992; Maier, 1993). See USDA-GIPSA conditions. These include insect population growth (1995) for complete recommendations on sampling. and moisture hot spots due to poor aeration through accumulated trash and fines generated by broken Grain Quality Degradation kernels. Damage can occur because of high velocity impact, kernel stress cracks during drying and cool- Preserving grain quality is a problem in many ing, and very dry or very cold grain. Proper selection parts of the world (Gras et al, 2000). Quality never and sizing of handling equipment such as augers and improves during storage. The best a manager can drag conveyors is essential in reducing kernel dam- hope for is to preserve the initial quality as closely age. Augers must be operated at the rated capac- as possible. Grain and feed can be stored for long ity and speed for the grain handled. Larger, slower periods of time if storage conditions are managed augers can reduce handling damage. Bearing-sup- correctly and the material is in good condition to ported augers make operating at rated capacity under begin with. When degradation occurs, swift inter- variable incoming flow rates much easier to achieve. An accumulating bin over the intake hopper for the auger also can provide a more constant feed rate by 2 K-State Research and Extension Chapter 10 | Drying, Handling, and Storage of Raw Commodities keeping the intake full. Level control switches allow content can be higher. If storage temperatures are the auger to run periodically at or near full capacity, expected to be high, as in summer harvested crops, minimizing mechanical damage. grain must be at lower moisture content to store suc- cessfully. Fall harvested crops generally can be stored Bucket elevators cause less damage to grain as long at higher moisture content because of low initial as drop heights are less than 40 feet. Above this ambient storage temperatures that usually continue height, grain damage is much more likely to occur. through the fall and winter months. The lower the Grain decelerators can be installed in downspouts to moisture content, the longer grain can be stored suc- reduce the grain velocity and subsequent damage. cessfully. Table 1 shows expected storage periods for grain held at various moisture contents. Properly installed and operated pneumatic conveyors reduce grain damage. Large drop heights, sharp Temperature management is affected by moisture spout turns and transitions, and misalignments are migration during the storage period. Convection air avoided that cause increased grain velocities, turbu- currents caused by temperature differences between lence, and high velocity grain impact that result in ambient conditions and the grain cause moisture damage, particularly to cracked or brittle seed. migration as warm moist air meets cool grain. Dif- ferences in temperatures surrounding grain bins due Storage damage to shading, temperature differences between day and night, and cold weather cause moisture problems Mold and insects are the primary causes of dam- within bins. Grain is a good heat insulator. The cen- age to stored grain. Grain in poor condition due to ter of the grain mass (or bulk) stays warmer longer improper management is a prime target for mold than grain near the bin walls. When the center of the growth and insect population increases. Damaged grain is warmer, convection air currents move down kernels, excessive fines, trash, and improper drying through the wall area of the grain and push the con- create conditions for spoilage. Pockets of fine

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