Grain Quality Management
Corn Moisture Shrink
& Total Shrink
Managing corn to ensure the highest grain quality can help put dollars in your pocket. Get tips on developing a plan to harvest, store and monitor grain to maintain the best possible quality and value.
|Critical Steps to Maximizing Corn Grain Quality|
The Value of High Test Weight Corn Grain
Field Facts written by Agronomy Sciences.
According to corn Extension specialists, low test weight grain may be due to any number of causes that reduce kernel fill: lower temperatures, leaf diseases or drought stress during the grain fill period, premature frost damage to late-developing fields and ear rots. Hybrid genetics also has a large influence on test weight. This article discusses test weight and its implications for grain marketing, transportation, storage, quality and feeding.
For Grain Trading, “Bushel” is a Weight Measure – Although “bushel” is technically a volume measure, grain is marketed by weight, not by volume. For this purpose, a “bushel” of corn is defined as 56 lbs. of grain at a moisture content of 15.5%. But because grain differs in kernel hardness or density, the volume occupied by 56 pounds of grain may vary substantially. Grain mass per unit volume, or density, is most important in grain transportation and storage. Denser kernels require less space, which means that fewer truckloads and storage bins are needed to store the same weight of grain. Denser grain also has higher quality characteristics for some end uses.
What is Test Weight? "Test weight" is simply a measure of grain bulk density. An official test weight measurement uses standardized equipment to determine the mass (weight) of a sample quart of grain, and then converts this to a pounds per volumetric bushel basis. Because transporting and storing lower density grain is more costly (on a weight basis), buyers discount grain if test weight is below the minimum standard set by the USDA (Table 1). In addition to density, test weight is affected by how kernels pack in a container, which is influenced by kernel shape and surface friction.
|USDA Corn Grade||Test Weight|
* Damaged kernels, % broken corn and foreign material also affect the USDA grade.
As the table shows, the minimum test weight for No. 2 corn is 54 lbs/bu. Loads testing below this minimum will usually receive a dockage at the elevator.
Figure 1. High test weight grain offers advantages in grain marketing, quality, transportation, storage and feeding.
Transportation and Storage
Higher weight per unit volume of grain has obvious advantages in harvest, handling and storage. More bushels fit in a combine grain tank, on a truck or in a grain bin. These advantages are demonstrated in the following example:
Compare 80 acres of a high test weight hybrid such as Pioneer® brand 35K04 with a low test weight competitor. Assume test weights of 56 lbs/bu and 52 lbs/bu for the 2 hybrids.
- The test weight advantage on a percentage basis is 11% (58 - 52 = 6; 6 / 52 = 0.11). Therefore, in a given volume you can hold 11% more of the Pioneer hybrid.
- A common semitrailer would hold about 900 bu. for the lower test-weight competitor, and 11% more, or 1000 bu. for the heavier Pioneer corn.
- If the Pioneer hybrid yielded 200 bu/acre this would fill 16 semi loads (200 bu/acre x 80 acres = 16,000 bushels. 16,000 bu / 1000 bu per semi load = 16 semi loads.)
- The same weight of corn for a competitive hybrid with test weight of 52 lbs/bu would require 18 semi loads to haul the grain. (16,000 bu / 900 bu per semi load = 17.8 semi loads.)
- The Pioneer hybrid will occupy 11% less space in the combine grain tank as well. For this reason, it is easy to assume that higher test weight hybrids are lower yielding, even when they are higher yielding. (Growers should also calibrate their yield monitors for high test weight grain as well as normal and low test weight grain to ensure accuracy.)
- A 40,000 bu grain bin would hold an additional 4,400 bu. of the higher test weight Pioneer hybrid.
Grain Quality and Feed Value
High test weight grain is generally considered to be higher quality because it is preferred by corn wet millers and food processors. In addition, some methods of determining corn breakage have shown less breakage with high test weight grain. Denser grain often has a higher proportion of starch-rich endosperm and a lesser proportion of bran and hull, resulting in a higher metabolizable energy content for livestock feed.
Test Weight and Moisture Relationship
Test weight and grain moisture are inversely related, at least in the range of 20% to 30% moisture where most corn is harvested. As corn dries, the kernel shrinks and becomes more dense, and the kernels pack tighter together due to less surface friction. Studies have shown that corn can gain up to 0.25 pounds of test weight for each point of moisture removed. For example, corn at 28% moisture with a test weight of 54 lbs/bu, may have a test weight of 56 lbs/bu when dried to 20% moisture.
How to Determine Corn Moisture Shrink and Total Shrink
Field Facts written by Curt Hoffbeck, DuPont Pioneer Area Agronomist
The weight reduction as grain is dried is referred to as "moisture shrink." Moisture shrink can be determined by multiplying a moisture shrink factor by the change in moisture. The moisture shrink factor is determined by the following equation:
|Moisture shrink factor = 100 divided by (100 minus percent final moisture)|
This factor represents the shrink that occurs for each percentage point of moisture removed from initial to final moisture. Moisture shrink factors based on final moisture content are shown in
|Final Moisture Content||Moisture Shrink Factor|
For instance, the shrink factor when drying corn to 15.5% moisture is 1.1834. Therefore, the moisture shrink when drying corn from 25.5% to 15.5% is 10 X 1.1834 = 11.83% (11.83% loss in grain weight due to the water removed during the drying of 25.5% moisture corn to 15.5% moisture.)
Example moisture shrink calculations: Assume we have 1,000 lb of 25.5% moisture corn, and we want to know how many bushels we would have at 15.5% final moisture:
Figure 1. Reduction of grain mass due to drying and handling losses is referred to as "shrink."
Note that shrink that is assessed when grain is marketed will likely be higher than the moisture shrink to include some facility operation costs and handling losses. Although most of the weight loss during drying is water, a small portion is dry matter. This loss is often called "invisible shrink," but may be better described as "handling loss." Some of the handling loss is due to loss of volatile compounds such as oils, mechanical losses from broken kernels and foreign material, and possibly also due to respiration of the seed itself. Handling loss will normally be far less than that due to water.
The actual amount of handling loss will depend on the initial physical quality of the corn, the method of drying, and the handling processes during drying. Research at Iowa State University determined that on-farm handling losses ranged from 0.22% to 1.71%. Losses from commercial drying systems ranged from 0.64% to 1.33%. The 3-year on-farm average was 0.82% compared to 0.88% for the commercial facilities.
Calculating Total Shrink
Shrink factors used by grain buyers account for both moisture shrink and handling loss. Grain buyers typically use drying tables or a constant shrink factor to "pencil shrink" the grain they buy.
Some grain buyers use drying tables which include moisture shrink and a constant handling loss, usually 0.5% of the initial weight of the grain. Using this method, the formula for calculating total shrink is: Total Shrink = (total moisture shrink) plus (handling loss).Example:
- If we were to dry shelled corn from 25.5% to 15.5% moisture (a removal of 10.0 percentage points), the total moisture shrink would be 10.0 multiplied by 1.183 (from Table 1), or 11.83% of the original grain weight.
- Add to this the 0.5% handling loss for a total shrink of 12.33%.
- Thus, if 1,000 lb. of 25.5% moisture corn were dried to 15.5% moisture, the total weight loss due to water and dry matter removal would be 123.3 lb. (1,000 multiplied by 0.1233).
- The resulting weight of the dried grain would equal 876.7 lb. (1,000 minus 123.3) or 15.6 standard bushels (876.7 lbs divided by 56 lbs/bu) using this shrink method.
Figure 2. The actual amount of handling loss of corn grain will depend on the initial physical quality of the corn, the method of drying, and the handling processes during drying.
Hicks, D.R. and H.A. Cloud. University of Minnesota, Calculating Grain Weight Shrinkage in Corn Due to Mechanical Drying. NCH-61, Purdue University, Cooperative Extension Service, West Lafayette, IN.
Grain Quality & Harvest
- Corn grain quality is increasingly important as more grain is used for processing and other specialty end uses.
- Corn grain quality is determined by hybrid, growing conditions, harvest practices and drying operations.
- Except for growing conditions, these quality factors are generally under the control of the grower.
- Harvesting grain at too high of moisture can result in severe kernel damage during threshing and drying.
- Conversely, allowing corn to field dry too long can lead to reduced yield and quality if stalk or ear rot diseases or insect feeding damage are increasing.
- Monitor stalk quality. If stalks lodge, ears can come in contact with the ground which can lead to ear rot development.
(Photo courtesy of John Deere.)
- Proper combine settings and operation are critical to preserve grain quality.
- Optimum ground speed depends on the condition of the crop, but should generally be as fast as possible without plugging the head or threshing mechanism.
- Snapping rolls should be set relative to ground speed. A setting that is too fast will cause kernels to be shelled and lost and increase breakage of ear butt kernels.
- Use the lowest possible cylinder/rotor speed that will shell the grain within acceptable loss levels (1% in good-standing fields.)
- Begin with manufacturer suggested sieve and fan settings and check and adjust frequently. Crop conditions can change rapidly during autumn days.
Grain Handling and Drying
- Broken kernels and fines can create problems during grain storage, and lower quality for many end uses.
- A rotary screen, gravity screen or perforated auger housing section can be used to screen out the fines.
- Stress cracking is the major quality problem associated with improper drying and cooling of grain.
- Kernels with a large number of stress cracks are more likely to be broken, produce smaller grits during dry milling, absorb water too rapidly during wet milling, and are more susceptible to insect and mold damage during storage.
- The wetter the grain the lower the temperature must be to maintain a better kernel quality and density.
- High temperature drying followed by fast cooling can have a devastating effect on stress cracking of corn kernels. For most grain uses, this drying method is unacceptable.
Effect of dryer method on stress crack formation.
Drying Method % Stress-Cracked Kernels Natural air and low temperature in-bin 5% or less stress-cracked kernels Medium temperature and slow cooling 10-25% stress-cracked kernels Medium temperature and stirring in-bin 15-35% stress-cracked kernels High temperature and fast cooling 60-100% stress-cracked kernels
Source: Postharvest Pocket Guide, Purdue Univ. Extension.
Maximum recommended kernel temperature during drying.
Product Maximum Kernel Temperature Shelled Corn - Animal Feed 130 F Shelled Corn - Wet Milling 100-130 F Shelled Corn - Dry Milling 100-120 F Shelled Corn - Snack Foods 100 F
Source: Pioneer Hi-Bred.
- When using a continuous-flow grain dryer and as colder temperatures approach, take caution in not overcooling the grain. This can cause stress fractures. Cracked and broken kernels don't store as well as whole kernels.
- Freezing temperatures can cause stress fractures in grain, especially in higher density kernels.
- After harvest, it's important to check your grain on a weekly basis for 4 to 6 weeks until you are sure it's stable.
- Selecting hybrids rated highly for grain quality traits is the first step in producing highest quality grain.
- Pioneer® brand hybrids are rated for resistance to prevalent ear rot diseases and test weight.
- High test weight is a grain trait that helps kernels resist breakage during threshing and handling.
Grain Moisture Management Pays Big Dividends
Field Facts written by David Pfarr, Zach Fore and Curt Hoffbeck, DuPont Pioneer Area Agronomists
Manage Grain Moisture for Enhanced Profitability
A bushel of corn is traded on the basis of 56 lbs. per bushel. A bushel of corn at 15.5% moisture contains 47.32 lbs. of dry matter and 8.68 lbs. of water. This is an important concept to remember because as corn becomes drier you are actually delivering more dry matter to the market and less water weight. While delivering bushels to the market at optimum moisture is important, it is only one of the factors determining moisture levels of corn going into storage.
According to Bill Wilcke, Extension Researcher at the University of Minnesota, corn stored up to 6 months should be dried to 15% moisture. Corn stored from 6 to 12 months should be dried to 14% moisture and corn stored for more than 12 months should be dried to 13% moisture. Due to temperature changes and moisture migration in the grain, storage structures must have adequate flooring and air movement to prevent grain from going out of condition. Fines must also be removed by prescreening or removing centers from bins.
Figure 1. Thorough management of grain moisture is critical to maximizing profitability when marketing grain.
Overdrying corn can lead to significant dollars lost due to added expense and less bushels to sell in the market. At 15.5% moisture and a market price of $3, a bushel of corn is worth 6.34 cents per lb. of dry matter. This same corn at $5 per bushel is worth 10.57 cents per lb. of dry matter.
If your goal is to store and market corn at 14.5% moisture and it is inadvertently dried 1 point less (13.5%) you have given up 3.8 cents/bu in today's market (corn at $3.25/bu). The drying cost for the extra point would be 0.02 gallons of propane at $1.50/gallon, which is 3 cents.
In this previous calculation you can see that fine-tuning the grain drying operation with extra attention and/or extra investment is worth over 8 cents per bushel. Consequently, a farmer harvesting and drying 100,000 bushels of corn and missing the mark by 1 percentage point of moisture will leave over $6,500 on the table.
How Much Yield Is Needed To Offset Drying Costs?
A number of factors determine the profitability of corn production. At harvest we are looking at primarily 2 factors — yield and moisture. There is often a trade-off between these 2 factors. Longer maturity hybrids often yield higher but are wetter at harvest. A good question to ask is:
'How much higher yield do you need to offset higher drying costs?'
It takes about 0.02 gallons of propane to remove 1 point of moisture per bushel of corn.
|You can use this formula to calculate the drying cost per acre:|
|bu/acre x points of moisture to remove x 0.02 x propane cost ($/gal) = $/acre|
The table below shows the bu/acre required to offset energy costs at different yield and moisture levels at a propane cost of $1.50/gal and a corn price of $3.25/bu.
At a yield level of 150 bu/A, it takes 2.8 bu/A to offset the energy costs to dry a hybrid that is 2 points wetter at harvest. Of course, energy cost is not the only factor to consider. There are also equipment and handling costs associated with drying.
More Best Practices for Managing Grain Moisture
Moisture testers: Grain farmers need to have an accurate and reliable moisture tester on the farm (Figure 2). In a single season, selling grain that is too dry by even half a percent could cost much more than a high-quality moisture tester. Even with a high-quality tester, growers should calibrate their meter with that of the point-of-sale.
Dickey-John GAC® 500 XT
Figure 2. Examples of moisture testers designed for on-farm use. Other products are also available, including refurbished commercial testers.
Grain dryers with manual settings need to be checked frequently with a good moisture tester to achieve the desired moisture levels. Computer-controlled drying systems rely on a moisture tester as a standard to calibrate sensors reading wet grain in and dry grain out. The amount of investment justified in precision drying systems and storage aeration will depend on the number of bushels that can be run through the operation.
Too wet or too dry? If growers had the choice of delivering grain that is 1 point too wet or 1 point too dry, they should choose "too wet," as the economics are overwhelmingly on their side. Delivering grain too dry results in losing all of the weight represented by the moisture differential. Delivering grain too wet incurs drying costs (some of which would have been spent to dry the grain on-farm) and shrink, but "weight" per se will not be lost.
Overdrying grain: Grain stored long term on the farm may be significantly lower in moisture than the maximum allowed by the grain buyer. In fact, even grain stored short term may be lower than required for some uses such as wet milling. Each end use (dry-grind ethanol, wet milling, long-term storage, etc), may have a different moisture allowance, and knowing that number is the first step in meeting it.
Figure 3. Various grain buyers may have different grain moisture requirements, depending on grain use and expected storage time.
If grain is too dry, some growers may have the option of blending or aerating the grain to adjust it to the maximum moisture allowed (up to 15.5%). The resulting moisture content of a uniform blend of 2 grain sources is the weighted average of the 2 grain moistures.
Increasing grain moisture content by aeration is usually only possible with very high airflow rates such as those common in natural air drying systems. Even then, successful moisture adjustment may require electronic control systems that run the fans when ambient temperature and relative humidity conditions dictate. In bins with limited fan capacity, increasing grain moisture may require months to accomplish, or may be impossible. In such cases, preventing overdrying of grain is even more important.
Grain drying and storage concerns, like other areas of production and management, can provide added opportunity for those willing to fine-tune their operations with an investment of time and/or capital.
Maintaining Corn Grain Quality Through Harvest and Drying
Crop Insights written by Steve Butzen, Agronomy Information Manager
- Corn grain quality is increasingly important as more grain is used for processing and other specialty end uses.
- Hybrid selection and timely harvest are important to produce high-quality grain. Growers should monitor both crop condition and moisture as grain dries down after maturity.
- Combine cylinder/rotor speed and other settings can have huge effects on grain quality. Start with manufacturer recommendations and readjust to crop conditions.
- Stress-cracking is the major quality problem caused by high temperature drying and rapid cooling of grain. Fractures in the corn endosperm lead to problems in both storage and processing.
- Stress-cracked kernels are more likely to be broken, produce smaller grits during dry milling, absorb water too rapidly during wet milling, and are more susceptible to insect and mold damage during storage.
- This Crop Insights discusses factors important to corn grain quality in the field, during combining and in drying. Grain storage recommendations are also included.
Corn grain quality is determined by hybrid, growing conditions, harvest practices and drying operations. Except for growing conditions, these quality factors are generally under the control of the grower. Grain quality, good or bad, largely results from cumulative grower decisions and practices from the field to the bin.
Good grain quality begins in the field with hybrid selection and harvest timing. Growers should pay close attention to crop condition after physiological maturity, as well as grain moisture. Poor quality grain in the field will only deteriorate further as it is handled prior to storage.
Modern combines can maintain grain quality achieved in the field when set properly and checked frequently. However, poorly adjusted combines can have a devastating effect on grain quality, especially if the grain is wet or light. Cracked or broken kernels are the usual outcome of a poorly adjusted machine. These damaged kernels often incur further breakage with subsequent handling. By storage time, an abundance of broken kernels and “fines” can restrict air flow and provide a ready substrate for insects and diseases.
Grain drying is critical to maintaining quality. High-temperature drying results in stress cracks in the kernel, especially if corn is cooled rapidly after heating in the dryer. With subsequent handling, stress-fractured corn begins to break, resulting in storage problems in the bin and lower value for end uses such as dry milling or wet milling.
Good grain quality begins in the field. If insects, ear rots, weather or other growing conditions have damaged the grain, quality will likely deteriorate further with harvest, handling and storage. Selecting hybrids with inherent grain quality attributes is the first step toward producing a quality crop. Scheduling harvest based on crop conditions as well as grain moisture is another field practice to help achieve the highest possible grain quality.
Hybrid Selection: Selecting hybrids rated highly for grain quality traits is the first step in producing highest quality grain. Pioneer® brand products are rated for resistance to prevalent ear rot diseases, test weight, and overall grain quality. Ear rot resistance is important to preserve grain mass and storability. High test weight is a grain trait that helps kernels resist breakage during threshing and handling. Selecting hybrids that excel in these traits is important to production of grain having dense, intact kernels with minimal breakage, disease and discoloration, especially for markets that pay a premium for high grain quality.
Harvest Timing: Harvest timing may have a major effect on grain quality in some growing environments. Harvesting grain at too high of moisture can result in severe kernel damage during threshing and drying. For that reason, grain quality experts suggest allowing corn to field dry below 20% moisture before harvesting. But allowing corn to field dry can also have negative consequences to both yield and quality if stalk or ear rot diseases or insect feeding damage are increasing. For that reason, many agronomists recommend to begin harvest when corn is around 25% moisture. The key to deciding which of these suggestions is appropriate for your fields is to closely monitor both moisture and crop condition beginning at physiological maturity.
In monitoring crop condition, growers should pay careful attention to potential ear, stalk and root problems. Many common corn disease pathogens such as Diplodia, Fusarium and Gibberella can attack both stalks and ears. These diseases, as well as anthracnose, often begin as root rots, or enter the stalk or ear through insect feeding ports. Stresses on the plant during ear fill, including drought, hail, limited sunlight, or even high grain yield weaken the plant and usually lead to more stalk rot development prior to harvest.
Stalk deterioration can impact both yield and grain quality. If stalks lodge due to storms or wind, ears can come in contact with the ground. This often provides both a source of inoculum and moist conditions for ear rot development.
Weak stalks can be detected by pinching the stalk at the first or second elongated internode above the ground. If the stalk collapses, this indicates advanced stages of stalk rot. Another technique is to push the plant sideways about 8-12 inches at ear level. If the stalk crimps near the base or fails to return to the vertical position, stalk rot is indicated. Check 20 plants in 5 areas of the field. If more than 10% to 15% of the stalks are rotted, that field should be considered for early harvest.
Strip back the husks on 5 plants in 5 areas of the field to check for insect feeding or ear rots. If these problems are severe, consider harvesting and drying grain to below 18% moisture to stop progression of both insects and diseases.
Combine settings and operation are critical to preserve grain quality. The combine is a complex machine that gathers, threshes, cleans and transfers grain. Poor combine adjustment can result in more beating, shearing or pinching of grain, causing broken and damaged kernels. When set properly, most combines, both cylinder and rotor types, can do a good job of separating corn kernels from the cob while leaving kernels intact and unbroken.
Growers are advised to set the combine to manufacturer-recommended settings as a starting point, and then adjust to the condition of the crop. Frequent checking and readjusting can then keep the combine set appropriately to both reduce crop damage and harvest losses. When crop conditions change during the day, small adjustments may be necessary.
The goal of proper combine settings is to achieve a smooth, even flow of crop material moving through the machine. The combine should run nearly full to minimize impact on the grain. A near-empty machine, on the other hand, leads to multiple contacts of the machine and the grain, which increases breakage.
Ground and Snapping Roll Speed: The ground speed depends on the condition of the crop, but should generally be as fast as possible without plugging the head or threshing mechanism. Snapping rolls should be set relative to ground speed. When set too fast, snapping rolls increase the impact of the ear on the stripper plates. This causes kernels to be shelled and lost, increases breakage of ear butt kernels and results in ear bounce.
Cylinder/Rotor and Concave: The cylinder or rotor is designed to thresh corn from the cob. It is no surprise then, that cylinder/rotor speed is the leading cause of grain damage by the combine. In 1 study, increasing the cylinder speed from 300 to 600 rpm increased kernel damage from below 5% to over 30%. However, if threshing is too gentle, unshelled kernels can be lost with the cobs.
Growers should use the lowest possible cylinder/rotor speed that will shell the grain within acceptable loss levels (1% in good-standing fields). To reduce unthreshed losses without increasing grain damage, try decreasing the concave clearance before increasing cylinder/rotor speed. If this does not achieve satisfactory threshing, then begin to increase cylinder/rotor speed as required.
Cylinder rasp bars can damage kernels, especially when new. Manufacturers suggest to break in the rasp bars for 50 hours in a crop where quality is not as critical. This break-in period will allow sharp, square edges to be rounded and smoothed. Avoid using the chrome-plated rasp bars that are much harder, retain their edges longer, and tend to chip and develop sharp edges that damage grain.
Augers: Several augers convey the grain through the combine, including the cross auger, the clean grain auger, the tailings augur and the unloading auger. Badly worn augers become sharp and can shear grain. Augers running at less than capacity can break and damage grain. To reduce grain damage from augers, replace badly worn auger flighting. Idle engine until unloading auger is filled, then increase throttle. Keep internal augers as full as possible by running the combine at capacity.
Separation and Cleaning: After threshing, the grain is separated from non-grain crop material by the chaffer and shoe sieves and the cleaning fan. Lighter chaff is blown out the back of the combine, while heavier unthreshed cob segments are returned to the thresher by the tailings system. Screens allow fine grain particles and foreign matter to be removed in the cleaning process.
The goal of separation and cleaning is to achieve a clean, high-quality end product while minimizing grain losses. To accomplish this, sieve and fan settings are critical. Begin with manufacturer suggested settings and check and adjust frequently. Crop conditions, including non-grain crop moisture, can change rapidly during autumn days. Monitor losses behind the combine and grain quality in the grain tank throughout the day.
Broken kernels and fines can create problems during grain storage, and also lower quality for many end uses. When corn is transferred from the grain cart to the dryer or bin, many growers use a rotary screen, gravity screen or perforated auger housing section to screen out the fines. While this is a useful practice, growers must also be aware of the potential for further occurrence of damaged and broken kernels in drying and grain movement.
Stress cracking is the major quality problem associated with improper drying and cooling of grain. Stress cracks are fine fracture lines in the endosperm of the kernel located just below the outer layer or pericarp. The amount of stress cracking that may occur depends on initial grain moisture, rate of moisture removal, maximum grain temperature reached in the dryer, and rate of grain cooling.
Kernels with a large number of stress cracks are more likely to be broken, produce smaller grits during dry milling, absorb water too rapidly during wet milling, and are more susceptible to insect and mold damage during storage. For this reason, minimizing stress cracks is a primary goal for maintaining end-use quality and long-term storage potential of corn. Table 1 shows the relative effect of various drying methods on stress crack formation.
|Drying Method||Stress-Cracked Kernels|
|Natural air and low temperature in-bin||5% or less stress-cracked kernels|
|Medium temperature and slow cooling||10-25% stress-cracked kernels|
|Medium temperature & stirring in-bin||15-35% stress-cracked kernels|
|High temperature and fast cooling||60-100% stress-cracked kernels|
Source: PostHarvest Pocket Guide, Purdue Univ. Extension.
As the table clearly shows, high temperature drying followed by fast cooling can have a devastating effect on stress-cracking of corn kernels. For most grain uses, this drying method is unacceptable.
Growers should carefully consider end use of grain when making decisions regarding drying temperatures. Table 2 shows the maximum corn kernel temperature limits for drying corn for various end uses.
|Product||Maximum Kernel Temperature|
|Shelled Corn - Animal Feed||130 F|
|Shelled Corn - Wet Milling||100-130 F|
|Shelled Corn - Dry Milling||100-120 F|
|Shelled Corn - Snack Foods||100 F|
See the following table for allowable dryer temperatures to keep kernel temperatures below the thresholds shown above.
Continuous Flow Grain Dryers*
|Product||Operating Plenum Temperature**||Grain Temperature Maximum|
|Food Corn||130 - 140 F||100 F|
|Wet Milling Corn||170 - 190 F||130 F|
|Livestock Feed||170 - 190 F||130 F|
* To maintain high capacity and grain quality, keep your grain dryer clean!
** Temperature ranges must be within 15 – 20 F anywhere within your plenum.
Dryeration: Dryeration is the process of allowing hot grain from a high temperature dryer to steep in a bin without airflow for about four to six hours prior to cooling by aeration. Not only does this process reduce the amount of stress cracks, but it also increases the energy efficiency of the system and can more than double dryer capacity. (Dryer capacity increases because corn leaves the dryer at a higher moisture, and does not tie up the dryer during cooling.)
Appendix I - Optimal Management Practices for Drying and Storage
Written by John Gnadke, AGS, Inc.
- In-Bin with stirring equipment - for best results, the operating temp should be 95-105 F.
- In-Bin with low-temp heaters (LP or electric) should be operated on a Humidity Controller. This will condition the ambient air to the proper relative humidity (RH). For best results, the RH setting is approximately 70%.
Natural Air In-Bin
- Fan Size: 1.5 CFM of air per bushel.
- Clean grain to 2% or less BCFM.
- Wet grain moisture: 20% for best results
- Roof Venting: 1.5 sq. ft. per fan HP.
In-Bin Continuous Flow
- Clean Grain to 2% or less BCFM.
- Operating Temp: 130-160 F.
- Keep grain depth from 4 to 6 feet for highest capacity of this unit.
- Proper roof vent is a must (1.5 sq. ft. per fan HP).
- Grain discharge temp will be 95-115 F.
- If stress fractures are a part of a grain contract, take special steps to prevent this from occurring (grain temp: 95-105 F).
- If wet grain is 20% or less, steep for 12 hours before cooling.
- If wet grain is 22-24%, steep for 18-24 hours before cooling.
- If ambient air temperatures fall below 40 F at night, then DO NOT operate cooling fans.
- Operating cooling fans at 40 F or above will reduce stress on grain (may require day-time operation of these cooling bins.)
Cooling Grain to Proper Storage Temperatures
- Cool grain to 35 F (DO NOT freeze food corn as it can cause additional stress on the grain.)
- Freezing grain at 18-20% moisture can cause ice crystals to form on the kernels.
- When temperature rises in February or March, ice crystals will melt and cause grain to go out of condition very quickly.
All stored grain should be checked on a biweekly (every 2 weeks) basis.
Appendix II - Grain Storage Principles
Written by John Gnadke, AGS, Inc.
- Dry grain to the "equilibrium" moisture level (15%).
- Use LOW temperature drying to minimize stress cracks.
- For ideal grain storage target 2% cracked/broken.
- Level the grain in the bin to minimize moisture accumulation at the top of the bin (core or use a mechanical "spreader").
- "Core" the bin by removing 10% of the total bin capacity after filling to remove fines that accumulate in the center. In the coring process try to keep the bin as level as possible.
- Cool grain as soon as it is dry to within 10 degrees of air temperature.
- Aerate the grain for 10 to 14 days after filling to ensure grain "equilibrium" has been achieved - based on 1/4 CFM.
- Monitor grain temperature and moisture regularly (minimum biweekly, preferably on a continuous basis with "in-bin" probes and visual inspection).
- Monitor grain for insect and rodent infestation on a regular basis (minimum biweekly).
- Keep cooling the grain on a regular basis until grain temperature reaches 35 F. Never cool grain below 32 F.
- Check grain regularly (minimum biweekly) while in storage. 1) Lock out power. 2) Climb into the bin, look, feel, smell, and walk on the surface. 3) If automated controls are used, biweekly inspections are still recommended to ensure controls are functioning properly.
- Aerate on a regular basis while in storage, discontinue fan run-time when temperatures fall below 32 F.
- In the spring, warm up grain with every 5 F temperature differential until grain reaches 45 F.
- If delivery dates are July-Sept., cover fan inlets in February to keep grain cool.
- During summer months, aerate during cool, dry nights to hold grain temperature down.