DIVISION OF AGRICULTURE RESEARCH & EXTENSION UJA--University of Arkansas System Agriculture and Natural Resources FSA1072 On­Farm Grain Drying Methods

grain production more attractive Sammy Sadaka, Introduction resulting in more producers and Ph.D., P.E. When grain is harvested from the more production. This increased sup­ Assistant Professor ­ field, it contains dry matter and water. ply is associated with a larger grain Extension Engineer While water is necessary for price swing between harvest and plant growth and grain production, non­harvest periods. Therefore, in Karl VanDevender, excess moisture after grain maturity addition to more control of harvest can lead to storage­related problems. timing, there are potential economic Ph.D., P.E. Grain moisture content is expressed advantages to on­farm drying and Professor ­ Extension as a percent of the grain weight. storage. Accordingly, several Arkansas Engineer For example, 100 pounds of 13% producers indicated their interest in moisture content rice contains 13 exploring the possible techniques of Griffiths Atungulu, Ph.D. pounds of water and 87 pounds of dry on­farm grain drying and storage. Assistant Professor ­ matter rice. Grain moisture con­ This fact sheet provides an overview Grain Processing tent and temperature play a key role of the basics of on­farm grain drying Engineering in determining safe storage life (see and storage methods. https://www.uaex.uada.edu/publications/ pdf/FSA1058.pdf). As a ru le, dryer grain and cooler temperatures increase safe Grain Drying Basics storage durations. In contrast, wetter grain and warmer tempera­ Storage Moisture Content tures increase the potential for pests, The first step in drying grain is insects, mold and fungi to reduce determining the desired, or target, grain quality and market value. grain moisture content level. Under Therefore, the primary objective of drying grain reduces safe storage grain drying and storage is to manage time, increases the potential for qual­ the temperature and moisture of the ity losses and increases the likelihood air around the grain to minimize of high moisture price dockages grain quality and market value losses upon sale. Over drying grain reduces while holding grain for better market income due to increased drying costs. opportunities. Maintaining grain qual­ In addition, since grain is usually sold ity requires drying the grain to safe on a weight basis, one of the expenses moisture content levels after harvest involved in drying grain is the “cost” followed by lowering and maintaining of the weight loss that occurs during the grain temperature within a few the drying process. This weight loss degrees of ambient air temperatures. by drying is referred to as “shrink” Arkansas Is and is expressed as a percentage of Our Campus Traditionally, on­farm grain the original quantity before it is dried. drying and storage has seen limited Shrinkage should be considered to use in Arkansas. However, recent accurately determine the total cost of changes in agricultural markets and mechanical drying. Shrinkage tables Visit our web site at: s .uada technological advances have made provide bushel weights for various http ://www.uaex .edu

University of Arkansas, United States Department of Agriculture, and County Governments Cooperating moisture content levels of grains (see https://www. uaex.uada.edu/publications/pdf/FSA­1078.pdf). When Temperature and Humidity choosing the desired target moisture content, safe As indicated earlier, air temperature and humid­ storage time, grain shrinkage and buyer’s require­ ity determine EMC level and thus the drying capacity ments should be considered. of the air around the grain. Since ambient air temper­ atures and humidities fluctuate over time, the EMC Grain conditioning by drying and cooling to target and drying potential of air also fluctuates. Therefore, ranges should begin immediately after harvest. If in drying systems that use ambient air (with or with­ possible, avoid leaving grain in carts and buggies for out low levels of supplemental heat), air temperature more than a few hours or overnight. As indicated and humidity should be monitored and used to deter­ earlier, grain temperature and moisture content dic­ mine when the drying system should be operated. If tate how quickly grain quality and market value are mismanaged, drying opportunities could be missed or reduced. Drying and cooling freshly harvested grain moisture could be added back to the grain environ­ will delay spoilage and must begin within 24 hours ment increasing storage risks and wasting the energy and preferably within 12 hours after the harvest. to run fans again to re­dry. The ability to heat drying air increases the oppor­ Equilibrium Moisture Content tunities to dry grain and provides more control over the grain drying and storage process. If the EMC of The moisture in grain creates vapor pressure. ambient air will result in grain drying, adding heat In a like manner, the moisture in the air around the will reduce drying time and lower the final grain grain also creates vapor pressure. Moisture moves moisture content. The reduced drying time is usually from areas of high vapor pressure to areas of low desirable. However, if mismanaged, there is an vapor pressure. This moisture movement continues increased risk of over drying grain. There is also until the vapor pressures in the grain and air are energy cost to run fans and heaters. If the EMC of equal. The point at which vapor pressure in grain ambient air will not result in grain drying, adding and air are equal is called the Equilibrium Moisture heat can provide drying that otherwise would not Content (EMC). The EMC is dependent on three fac­ take place. As a result, the decisions of what type of tors: air temperature, air relative humidity around grain drying/storage system to install and when to the grain and grain type. EMC values for grain run fans and/or heaters become a process of balancing decreases as air humidity decreases or air temperature risks and economic inputs. increases (see https://www.uaex.uada.edu/publications /pdf/FSA­1074.pdf). Thus, grain drying will occur For manually controlled systems, the temperature as long as the EMC is less than the current grain for determining EMC should be an average tempera­ moisture content. If the EMC is greater than current ture over the drying period. The relative humidity grain moisture content, drying will not occur. Instead, should be the average expected during the drying additional water will be added to the grain bin. Water period. However, several companies make automated will increase the potential for mold and needs to be grain drying controls which measure grain moisture, removed as soon as possible. air temperature and air humidity. These automated controls can take much of the “guesswork” out of grain drying. Temperature can be read with a ther­ mometer in the plenum or on the farm. Ideally,

KEY CONCEPTS temperature and relative humidity should be mea­ l Moisture moves from high to low vapor sured on farm, but local weather information has pressure areas. been used in the decision­making process with acceptable results. l Grain drying occurs when the vapor pressure in the grain is greater than the vapor Evaporating moisture from grain requires energy pressure of the air surrounding the grain. in the form of heat. In general, it takes 1,100 BTUs of heat to vaporize one pound of water at 100% effi­ ciency. Heat energy can be supplied by the natural heat content of air or by supplemental heating. The If the current air conditions will not result in amount of moisture that air can absorb and transport grain drying, the easiest way to adjust EMC is by as it moves through the grain column is dependent heating the air. Heating air lowers the air relative primarily on EMC along with some influences from humidity and thus lowers the EMC and decreases air velocity, the distance the air travels and grain drying times. As a result, after heating air the new moisture content. As air moves through the grain relative humidity must be measured or calculated column, it absorbs moisture and thereby loses some before determining the new EMC. or all of its drying capabilities. grain to a certain moisture content and then harvest Grain Drying Options and dry further or market the grain at harvest. The Grain drying strategies can be divided into the disadvantage with this method is the reduced control following approaches: field drying, natural air drying, of the drying process and potential exposure to low temp drying, high temperature drying, and com­ weather and pests which causes damage. In addition, bination or dryeration. Allowing the grain to dry in over drying grain usually increases shatter and the field is the most widely used method. In many losses during harvest. Field drying should be used to cases, partial field drying is often used in conjunction manage grain moisture at the time of harvest. The with post­harvest drying to reach target storage time of year grain reaches maturity and the weather moisture content. Natural air/low temp grain drying conditions can have a major impact on how quickly is best described as filling or partially filling bins the grain will dry to a moisture content acceptable with freshly harvested grain, then running fans to for storage or sale. force air through the bins until the desired moisture content is achieved. High temperature drying is either conducted in the bin or within a pass dryer. Natural Air Drying Air is heated to high temperatures and forced Natural air drying is the most common on­farm through the grain until the grain dries. Combination drying method in Arkansas. It refers to the process and dryeration is done by partially drying grain with in which grain bins are filled or partially filled with high temperature dryers, and then the remainder grain and then natural air is moved through the of the drying process is done with low temperature grain with fans (Figure 2). This is typically done in air and fans. Each method has its advantages and bins equipped with a perforated floor, drying fan, disadvantages. In general, more drying process con­ grain spreader, sweep auger and unloading auger. trol reduces potential risk. However, an increase in Stirring devices may also be added. However, they control is usually associated with increased invest­ are not economical for natural air drying systems in ment costs and energy costs (Figure 1). most grain­producing areas because over drying is usually not a significant problem. Loading the drying FIGURE 1. General relationships among manage­ bin may be accomplished by either a portable auger ment control, initial investment cost and operational or a bucket elevator. The loading rate should be energy costs for various grain drying approaches. sufficient to empty a large trailer truck in no more than 2 hours, thus a minimum of approximately Combination 500 bu/h capacity. .... and Dryeration V, 0 u As dry (lower vapor pressure) air passes wet .... High Temp C (higher vapor pressure) grain, moisture moves from QJ Bin Drying ....E the grain into the air. The addition of water to the air V, reduces its ability to dry the grain it passes through QJ > Natural Air/Low next. This process continues as the air moves through C Temp Drying the column of grain until the air no longer dries the grain, or the air exits the grain. As the fans continue Field to run, a drying front moves from where the air Drying enters the grain to where it exits the grain. Behind the drying front, the grain is at EMC. Ahead of the drying front, the grain is above EMC. The vapor Control Over Drying Process > > pressure and flow rate of the air entering the grain determine the formation of this drying front and how quickly it moves through the grain. The air flow rate Field Drying depends on fan properties as well as the type and Grain drying begins in the field after the grain depth of the grain. As grain depth increases, air flow is fully mature. A layer of tissue is formed between rates decrease. Therefore, increasing grain depth the seed and the plant which blocks additional mois­ slows the drying front and increases the amount of ture and nutrient inputs from the plant. At this time it takes for all the grain to reach EMC, and the point the maximum grain quality and yield are set. potential for grain quality losses. Once the grain matures and the layer of tissue is formed between the seed and the plant, the sun and A common mistake with natural air drying is air can remove moisture and dry grain at a rate of to add too much grain to the bin at once. This will ½ to 1 percent per day. Once moisture reaches near increase drying times and delay the grain drying storage goal level, drying slows. Drying using this process which increases the likelihood of grain qual­ method is very common. Most producers field­dry ity losses. Therefore, it is commonly recommend to only add 4­5 feet of grain to a bin at a time. Then constant. This results in a lowering of the relative avoid adding more grain until the layer is dry. humidity of the air and allows for a possible net Depending on the system setup, several bins can be transfer of moisture from the grain to the air. Mois­ loaded alternatively, or the dry grain can be moved to ture transfer continues until the grain and air come another bin. into equilibrium. In grain drying, the drying fan con­ tinuously supplies air as moisture is transferred from Successful grain drying with natural air is usu­ the grain and removed from the bin. With low tem­ ally the most energy­efficient method of drying. It is perature drying, sufficient heat is added so that also the slowest method and has the greatest poten­ drying can continue until normally acceptable final tial for grain spoilage. Consequently, natural drying moisture contents are reached. requires the highest level of management if spoilage and/or aflatoxin problems are to be prevented. Much In this method, a perforated floor is required. of the risk is because there is little “reserve” capacity A grain spreader, under­floor unloading auger and for speeding up the drying process in that the inlet sweep auger usually are included. A stirring device air conditions vary with the weather. Typically, the may also be added. Filling the bin may be accom­ bin is filled only once each harvest season. If spoilage plished by either a portable auger or a bucket begins, the mid­course corrections are limited to elevator. either (1) drying immediately using another drying method or (2) selling before the grain degrades In low temperature drying, grain is dried and because of unacceptable damage levels. stored in the same bin, thus minimizing handling and labor costs. Generally the comparative total cost for drying decreases as less energy is used to heat the Low Temperature Drying drying air even though more energy is required to Low temperature drying refers to the process in operate the drying fans. Thus, successful low temper­ which grain bins are filled or partially filled with ature drying is relatively economical in terms of grain and then air with little (<10°F) heat added is energy costs when compared to higher temperature moved through the grain with fans (Figure 2). This methods. Some of this advantage is lost when electric­ is typically done in bins with a perforated floor or ity is used as the thermal energy source because it is ducts. Usually, electricity is the thermal energy usually more expensive than LP gas on per unit of source, hence the term “electric drying” is sometimes energy basis. used instead of “low temperature” drying. However, LP gas and solar energy may also be used as thermal Successful low temperature drying is defined as sources. drying the grain to a desired moisture content with­ out excessive economic losses through either energy The low temperature drying method is assumed costs or grain spoilage. Potential for drying increases to always have potential for drying grain within the when adding heat to increase the drying air tempera­ accepted moisture contents associated with long­term ture. Unfortunately, the rate of grain spoilage also storage. This is contrasted with natural air­drying increases with higher temperature. Thus, low temper­ where outside air conditions may not allow further ature drying is generally restricted to conditions drying. When air is heated, its temperature and where grain moisture is relatively low, nearly 20% volume increase, but its moisture level remains for corn. Low temperature drying has little reserve capacity; that is the system dries grain at a low steady rate that cannot be altered greatly. The FIGURE 2. Grain bin utilizing natural air/low dependability of the system is reduced further if temperature drying. solar energy is the heat source.

Perhaps the greatest risk associated with low temperature drying is the year­to­year variability of weather. The same drying strategy may not be used every year. Care should be taken to avoid aflatoxin contamination.

t t t Moist Air t t t High Temperature Drying Wet Grain Layer High temperature drying is done either in the bin Drying Zone or in a dryer. There are four approaches to high tem­ perature drying: in­bin batch drying, recirculating bin Dry Grain Layer 11----,1'1¥ +­ drying, continuous flow bin drying and pass drying. +- t t t Dry Air t t t ~-T"""l'-T"""l'""-1:::In­bin batch drying is similar to natural air/low tem­ perature drying except that air temperatures are often 120°­160°F and air flow rates are from 8 to Pass drying (Figure 5) is typically the fastest 15 cfm/bushel. Drying time is greatly reduced with method for drying grain. Most grain elevators use high temperature drying. However, grain near the some form of pass dryers to dry large amounts of floor often becomes excessively dried while the top grain quickly. This method requires the highest layer of grain often stays moist. Stirring devices pro­ energy inputs of all drying methods. The biggest vide more uniform drying and should be considered in benefit to using pass dryers is the large volumes of conjunction with this method. Stirring also allows for grain that they can dry. When used in conjunction increased batch depth (7­8 feet). with a short­term wet grain storage bin, grain can be harvested at a rate that exceeds the capacity of the Recirculating bin dryers (Figure 3) are bins that pass dryer. Then when harvesting pauses, such as at are filled with grain and then the fans and heat are night, the dryer which runs continuously empties turned on. There is a sweep auger in the bottom of the wet holding bin. While pass dryers tend to be these bins that is activated by temperature or mois­ the most expensive drying option, they do have the ture sensors. When a target condition is met, the advantage of providing the most control during grain sweep auger makes one full pass and stops until harvesting and drying. Pass dryers are made in sev­ those conditions are met again. Grain discharged by eral models including some portable models mounted the sweep auger is placed onto the top of the grain on trailers. Due to the higher temperatures (180° to within the bin. Some rewetting of dried grain may 220°F) being used, the potential exists to dry the take place causing inefficiency concerns. grain too rapidly or too much and cause cracked grain or other problems. However, with proper manage­ FIGURE 3. High temperature drying with grain ment, high grain quality can be maintained providing recirculation within the bin. the opportunity to market higher quality grain. Recirculating Bin Dryer

FIGURE 5. Pass dryer diagram.

Wet Grain Supply i Drying Heated Air Columns with Chamber ! ! ! ! Perforated "_,,/,,j'"~ X / ' ' Walls \ \ i +-: ( '- ,r I :..,. +- -+ I I I I 1 I -+ I-+ Moist - +-1 , Dry ' i Air Sweep Auger- I 1-+-- -+ I 1-+ +-: l Air 1 : +-1 ,it ~ / I ,,," .," Continuous­flow bin dryers use the same bin Conveyor for Moving ,,., setup as the recirculating bins except sweep auger Dried Grain to ~-~,-,,. .," )l grain is discharged into a cooling bin. High tempera­ ,.,, Cooling/Storage Bin / ture bin drying tends to be more efficient than other ~ high temperature drying processes because the heat is used to dry grain at the drying front which then continues up the grain column to aid in drying before being discharged. (Figure 4) Dryeration and Combination Drying Combination drying and dryeration (Figure 6) FIGURE 4. High temperature drying with separate are done by moving grain directly from either a drying and cooling/storage bins. pass or heated bin dryer and into an aeration bin at Cooling/Storage Bin Continuous-Flow Dryer 1 or 2 moisture points higher than the final desired moisture content. For dryeration, grain is allowed to temper without airflow for 4 to 6 hours. During this time the moisture content within individual kernels equalizes. .j, .j, Once the first grain that was placed in the bin Cooling .j, .j, .j, ,I. Dryer has tempered, cooling fans are turned on while addi­ Fan \ \ Fan -+ tional hot grain is added to the bin. The cooling front moves slowly up through the grain so that all grain within the bin has ample time to temper. The cooling fans dry grain the remaining 1% to 2%. This process Further Reading maintains grain quality better than using high Backer, L. F., R. C. Brook, H. A. Cloud, K. J. Helle­ temperature dryers alone. Individual grain kernels vang, B. A. McKenzie, W. H. Peterson, R. O. Pierce, redistribute moisture throughout the kernel during G. L. Riskowski and L. D. Van Fossen. MWPS­13 the tempering process, which is followed by lower Grain Drying, Handling, and Storage Handbook. temperature drying reducing stress to individual Second Ed. Ames, IA. Mid. Plan Ser. 1988. Print. kernels. Combination drying is essentially the same Hellevang, K. J. 1994. Grain Drying. North Dakota as dryeration yet it does not have a tempering step. State University Agriculture and University Both of these methods can significantly reduce energy Extension. November 1994. AE­701. use and increase dryer capacity. https://www.ag.ndsu.edu/graindrying/ publications/ae­701­grain­drying FIGURE 6. Combination and dryeration system Hellevang, K. J. et al. MWPS­29 Dry Grain Aeration diagram. The final stage bin is where the tempering, Systems Design Handbook. Revised First Edition. final drying and cooling take place. Ames, IA. Mid. Plan Ser. 2007. Print. Huffman, C. J., J. H. Pedersen, W. F. Wilcke, P. W. Wet Sacco and C. B. Soballe. MWPS­22 Low Tempera­ Grain Final ture and Solar Grain Drying. First Ed. Ames, IA. Bin Stage Mid. Plan Ser. 1983. Print. Pass Bin Loewer, O., T. Bridges and R. Bucklin. 1994. On­Farm Drying and Storage Systems. ASABE. Mckenzie, B. A., and G. H. Foster. 1980. Dryeration & Cooling Bin Cooling Systems for Grain. Purdue Univer­ Fan sity Cooperative Extension Service. 1980. AE­107. t t t t t Sadaka, S., and R. Bautista. 2014. Grain Drying Tools: Equilibrium Moisture Content Tables and Psychrometric Charts. FSA1074. https://www.uaex.uada.edu/publications/pdf/ FSA­1074.pdf Sadaka, S., G. Atungulu and G. Olatunde. 2016. Summary Safe Grain Storage Period. FSA1058. Production priorities and degree of grain quality https://www.uaex.uada.edu.publications/pdf/ control must be considered when choosing a grain FSA1058.pdf drying system. If initial cost is the highest priority, Sadaka, S., G. Atungulu and G. Olatunde. 2016. the producer should consider field drying or natural Understanding Grain Shrinkage and Expansion. air or low temperature drying. If the main goal of the FSA1078. https://www.uaex .uada.edu/ producer is to get the crop out of the field as quickly publications/pdf/FSA ­1078.pdf as possible, high temperature drying should be evalu­ Wilcke, W. F., and K. J. Hellevang. 2002. Wheat and ated. If grain quality is the priority, dryeration and Barley Drying. University of Minnesota Coopera­ combination should be considered. As with any tive Extension Service. 1992. FS­05949­GO investment, costs and returns can be spread over a number of years.

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SAMMY SADAKA, Ph.D., P.E., is an assistant professor ­ Issued in furtherance of Cooperative Extension work, Acts of May 8 Extension engineer and KARL VANDEVENDER, Ph.D., P.E., is and June 30, 1914, in cooperation with the U.S. Department of a professor ­ Extension engineer with the University of Arkansas Agriculture, Director, Cooperative Extension Service, University of System Division of Agriculture located in Little Rock. Arkansas. The University of Arkansas System Division of Agricul­ GRIFFITHS ATUNGULU, Ph.D., is an assistant professor ­ ture offers all its Extension and Research programs and services grain processing engineering with the Food Science Department without regard to race, color, sex, gender identity, sexual orientation, located at the University of Arkansas in Fayetteville. national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an FSA1072­PD­5­2017RV Affirmative Action/Equal Opportunity Employer.