Lusas high as 100°C (212°F). The temperature of soybeans must 25% in the confectionery type. At an ERH of 70% and not exceed 76°C, since discoloration and protein denatura-25°C, the former contains 9.6% moisture and the latter tion will occur [47]. Seed going into storage should not be 13.6% moisture; at 60°C moisture the contents are 8.1 and heat damaged so it will not respire or germinate. 10.9%, respectively [61]. Drying is energy-intensive. Reasonably efficient com-The general practice is to dry seeds to about 75% RH mercial dryers require 830-890 cal/kg (1500-1600 Btu/lb for interim storage, but some oil mill supervisors prefer of moisture removed) [59]. 65% RH for long-term (12 months) storage, especially in The prime factor to be controlled in stabilizing seeds is colder climates. Table 9 shows the maximum moisture lev-relative humidity (%RH), which is the weight of moisture els considered safe for selected oilseeds [62]. Antimicro-per unit weight of air in the atmosphere surrounding the bial preservatives are commonly used in prepared feeds, seed compared to the maximum weight possible (satura-especially during high-humidity summer months, and tion) at that temperature expressed as a percentage. The some farmers preserve high—moisture-content cereals and term equilibrium relative humidity (ERH) simply means oilseeds with propionic acid for feed use. The oilseed RH in the adjacent air after allowing sufficient time for crushing trade does not accept treated seed. moisture in the seed to equilibrate with the air, and can be Relationships between RH and equilibrated moisture determined by analyzing the head space in a sealed equili-content are shown for soybeans in Table 10 [63]. Levels to brated container. Another allied term is water activity, Av„, which soybeans will equilibrate, in various temperatures which is ERH expressed as a decimal rather than a per-and RHs of the surrounding air, are shown in Figure 3 [64]. centage. Direct-reading instruments are available for Relationships between temperature, moisture content, and measuring RH, ERH, and A. Manual methods for deter-allowable storage time of soybeans are shown in Figure 4 mining RH include the use of a sling psychrometer to ob-[64]. tain "wet bulb" and "dry bulb" temperatures and reference to relative humidity charts. Unfortunately, many people 5. Storage still prefer to relate seed stability to percent moisture con-Designs of storage (Fig. 2C) facilities are dictated by needs tent—a far less meaningful measurement. for aeration of seed and its angle of repose—the minimum Bacteria and yeasts have much higher ERH require-angle in degrees at which a pile maintains its slope [65]. ments for growth than molds (fungi). Table 8 shows that This sometimes is reflected in the pitch of conical roofs on some fungi will grow at any of the relative humidity ranges storage bins. Similarly, downspouts and the conical bot-shown, although few toxin-producing fungi grow at below toms of bins must have pitches steeper than the angle of 75% RH [60]. repose for the respective seed or meal to flow smoothly. During equilibration, available water from the seed and Higher moisture and oil contents increase the angles of re-atmosphere is attracted to the water-absorbing seed com-pose. Angles of repose and bulk densities of some major ponents but not to the oil. Thus, high-oil-content seeds oilseeds and products are presented in Table 11. (peanut, sunflower seed, and rapeseed/canola) must be Readily flowing seeds typically are stored in vertical-dried to lower moisture levels for safe storage than lower-walled silos. In contrast, undelinted cottonseed from the gin oil-content seeds like soybeans. For example, oil-type sun-is stored on cement floors in piles whose shape is dictated flower seeds contain about 42% oil, compared to about by its angle of repose. In areas with wet falls, winters, and TABLE 8 Equilibrium Moisture Contents of Common Grains, Oilseeds, and Feed Ingredients at 65-90% Relative Humidity (25°C) and Fungi Likely to Be Encountered Equilibrium moisture contents (%) Relative Starchy cereal seeds, humidity debated oilseed Peanut, sunflower (%) meals, alfalfa pellets Soybean seed, Rapeseed/Canola Fungi 65-70 12-14 11-12 6-8 Aspergillus halophilicus 70-75 13-15 12-14 7-10 A. restrictus, A. glaucus, Wallemia sebi 75-80 14-16 14-16 8-11 A. candidus, A. ochraceus, plus the above 80-85 15-18 16-19 9-13 A. flavus, Penicillium spp., plus the above 85-90 17-20 19-23 10-16 Any of the above Ref. 60.