Document MoaZrZzOzqYzVm7d1KGpg76Dj

134 CHAPTER 9 Table A .... Effect of Heating Chopped Alfalfa* - on Carotene Loss during Subsequent Storage of Meai at 212 F Initial carotene PP-ra- Carotaa* retained 1 week--149 F i "1 2 3 4 6* n _ 229 - - 228 197 176 149 1 `112 86 * Freeb-frraeo alfalfa from Ryer Island, California. 37 37 .37 28 21 18 15 1965 Guide And Data-Book protein nutritive value with air-having temperaturee ae high as 840 F provided that the air flow rate is approximately 110 cfm per bushel so that the average moisture of the batch is reduced to safe storage lead in about 1$ hr or with air having temperatures up to 180 F with air flow rates of 50 cfm per bushel so that drying.is accomplished in about 8 hr. The market grade of com may be affected more rapidly by growth of microorganisms than by any' other factor, except insect and'rodent damage.' Microorganisms will not grow'in grain at safe storage moisture content. . > Grain uniformly dried to safe moisture levels (see Table 1) is less subject to insect 'damage during storage than 'grain containing pockets of high moisture. Rodent damage can be eliminated by good housekeeping and the. use of effective poisons. ' *' - ! The rate of growth of microorganisms such as molds and bacteria is a function of grain moisture, temperature, and available'food or physical damage of the seed coat. Growth can be thought of as an oxidation process resulting in the produo Table 5..........Effect of. underdrying and overdrying on carotene stability in a commercial dehydrator Met . temper- F. Dehydrator control ' gage' Moisture % . Initial carotene* PP . 800)." .1M,2o00o1r .l,530f 1,540 l,500j Normal '* (10.9 I 9.8 J 7.6 J 7.0 7.6 l 6.3 308' 260* 282' 255 211 301 '29 .' 2Sf 27 29 31 26 1,200 Slightly wet . Normal Normal Normal Slightiy scorched 10.9.. . 260 : 10.2 237 ' '9.0 188 8.3 - 181 7.9 j. 212 . . 31 29 29 37. 32 1,400- Slightiy wet Slightly wet Normal Norma) Normal Slightiy scorched Scorched- 10.9 11.9 6.9 8.8 9.0 8.7 5.7 190 24 - - 127 ' - 29 . 292 33 302 . 29 159 29 . 172 . . 28 ' is?..; i" 38 1,600 ' t Wet .. r 21.3- 194 .28 1,600 Normal 6.1 256 30 1,600 .1 Slightiy scorched 4.7 V. 37 * Convcted (or motetai*. *- Fig. 11.... CO, Production of Field-Shelled Com tion of carbon dioxide. Since, the evolution of carbon dioxide can be readily measured, it can be used as an index of de terioration. Saul reports that field-shelled com will be safely dried if no more than 8 grams of carbon dioxide is produced per kilogram of dry matter. fig. 11 shows curves of data obtained by Steele and Saul on the production of carbon dioxide at 65 F in field-shelled com at moistures ranging from 28 to 18.8 percent. They obtained similar data for temperatures rangmg from 35 to 90 F. The data curves for all temperatures and. moistures measured were referred by the use of multipliers to the reference curve shown in Fig. 11. Fig. 12 is a plot of tire temperature multi pliers or relative deterioration-rate due to temperature, fig. 13 is a plot of the relative deterioration rate due to moisture. These are related in the following manner: TM ~ UMOM . <U) rjr " time required to produce CO, at specific moisture con tent ana temperature, hours. tm " time required to produce a given quantity of CO, as read from Fig. 11, hours.- M. = percentage moisture content, wet basis. T " Temperature Fahrenheit. Rt " relative deterioration rate due to temperature. Ra *= relative deterioration rate due to moisture. Example 1: Predict the time required for 28 percent moisture corn at 55 F to produce 8.0 gms perltflogram of dry matter. Solution: The time required for the reference sample to produce 8.0 gins CO, is 158 hr, from Fig. 11. The relative grain deteriora tion rates are 0.52 for 55 F and 1.42 for 28 percent moisture.- The predicted time for 28 percent moisture com at 55 F. to produce 8.0 gms CO, is equal to the time for the reference to produce 8.0 CO, divided by the product of the relative rates, or:1. re 158 ' " (Rt)(Rm) " (1.42)(0.62) " 214 ^ , This allows prediction of the time available for.safely drying field-shelled com. Twenty-eight percent should be dried within 214 hr if the average wet-bulb temperature of the drying-air is 55 F. Cotton Drying The desirable lint moisture content for best results in gin ning cotton appears to be 5-7 percent with an optimum moisture content of 6 percent. Since cotton is very hydrin scopic, it should be dried just prior to ginning. The wide vari- physiological :Factors in Drying and Storing Farm Crops 135 ation in incoming moisture content usually requires different' amounts of drying for each load. Rapid changes in the amount of drying required can best be bandied by the use of a multipath drying tower in which the cotton is exposed for various Ungths of tim* (2-10 sec) at temperatures not to exceed 350 F. The aiMo-cotton ratio may range from 40-100 cfm of air per pound of cotton. The germination of cottonseed is unimpaired by drying provided the internal cottonseed temperature does not exceed 140 F. This temperature is not exceeded- in the tower drier jayrtW-d above. However, the moisture content of the seed may be above the recommended level of 12 percent following the multipath tower drying. Drying seed in a triple-pass drum at 250-300 F with an exposure time of 4 min, followed by cooling, has been effective in reducing moisture "content, inhibiting the formation of free fatty acids, and improving germination over undried seed. Peanut Drying Peanuts will normally have a moisture content of about 50 percent at time of digging. By allowing the peanuts to dry on the vines in the windrow for a few days, much of this water will be removed. However, peanuts will normally contain 20-30 percent moisture when removed from the vines and some artificial drying is necessary. Drying should begin 6 hours after harvesting to keep the peanuts from self-heating. Both the maximum temperature and the rate of drying must be carefully controlled to maintain quality. High temperatures result in off-flavor or bitterness. Too rapid drying without high temperatures results in blandness or the lack of capacity of the nuts to develop flavor on roasting." High temperatures, rapid drying or excessive drying will also cause the skin to slip easily and the kernels to become brittle. These conditions result in high damage rates in the shelling operation and can be avoided if the moisture removal rate does not exceed | percent per hour. Because of limitations, continuous flow drying is not usually recommended for peanuts. Rice Drying Of all grains, rice is probably the most difficult to process without loss of quality. Rice containing more than about 12 percent moisture cannot be safely stored for long periods, yet the recommended harvest moisture content for best milling and germination ranges from 20-26 percent. When harvested at this moisture content, drying must be begun promptly to prevent the .rice from souring.' fig. 13 .... Relative Grain Deterioration Rates with Moisture Content Since the market for rice is for polished whole kernels of rice, it is necessary to prevent damage in the form of stress cracks produced by rapid moisture removal. Head yield is the percentage of rough rice which can be milled as unbroken kernels. Schmidt and Hukill report that best milling results were obtained with drying air with saturation deficits between 1.0 and 2.0 inches of mercury.** Saturation deficit is the dif ference between the saturated water vapor pressure at the dew point and at the dry-bulb temperature of the air. REFERENCES 1 J. A. Anderson and A. W. Alcock: Storage of Cereal Grains and Their Products (American Association of Cereal Chemists, Monograph Series, VoL 11, 1954). * USDA Air Oven and Water Oven Methods Specified in the Offi cial Gram Standards of the U. S. for Determining the Moisture Content of Grain (Service aid Regulatory Announcement No. 147, revised 1941, p. 3). * Official Methods of Analyses (Association of Official Agricul tural Chemists, Washington, D. C., 1960, 9th ed.). S. T. Dexter: A Method for Rapidly Determining the Moisture Content of Bay or Grain (Michigan Agricultural Experiment Station Quarterly Bulletin, Vol. 30, No. 2, 1947, p. 158). * G. W. Tanarw D. E. Wiaot: A Rapid Drying Oven for De termining the Moisture Content of Crop Samples in the Field (Re printed from the Quarterly Bulletin, Michigan Agricultural Ex periment Station, Michigan State University, East Lansing, . VoL 41, No. 3, February 1949, p. 600). ^ * G. W. Thua/* and D. E. Wiant: An Averaging-Type Meter for Measuring the Moisture Content of Hay tn the Windrow. (Re printed from the Quarterly Bulletin, Michigan Agricultural Ex periment Station, Michigan State University, February 1949, p. 608). T B. C. Haynes,' Jr.: Vapor Pressure Determination of Seed Bygroscopicity (Technical Bulletin No. 1229, ARS, USDA, January 1951). * S. M. Henderson: A basic concept of equilibrium moisture (Agricultural Engineering, Vol. 33, January 1952, p. 29). * W. V. Hukul: Basic principles in drying corn and grain sorghum (Agricultural Engineering, Vol. 28, August 1947, p. 335), (Also m J. A.-Anderson and A. W. Alcock, Storage of Cereal Grains, AACC, St. Paul, 1954). UG. L Nelson: A new analysis of batch grain dryer perform ance (American Society of Agricultural Engineers Transactions, VoL 3, No. 2, 1960, p. 81).