Drying Corn

Corn harvest is an exciting, busy time of year that can be stressful, but is still extremely fun. There's never enough hours in the day to get what needs to be accomplished done and all hands are on deck. This is a photo of my family helping out with corn harvest in 2012. 

More often than not, corn harvested in the Midwest will require some drying so it won't become moldy over the winter and next summer while farmers store it. Corn dryers work kind of like a dryer for your laundry. The dryer heats up to eliminate all the moisture in the grain; at least that's the goal. 

Corn dries for different lengths of time based on the maturity level and moisture percentage of the corn when harvested. To efficiently dry corn, you have to be careful not to damage the corn kernel but still adsorb all the moisture. The drying process should also be done in a timely manner as to not slow down the harvest and be completed before snow and winter. Overall, farmers want to make the corn safe to be stored for an extended period of time and can be sold at highest possible quality to the end user. 

Corn that is at 23% moisture or higher, should not be stored in a grain bin because it could freeze together over the winter, resulting in clumps of corn that won't unload easily or at all. The chart below illustrates the suggested number of days that corn should be dried. The numbers across the top show temperatures, and the ones on the left side are the percentage of moisture in the corn.

"Approximate" Allowable Storage Time (Days) for Cereal Grains

	Temperature (F)
M.C. (%)	30	40	50	60	70	80
14	*	*	*	*	200	140
15	*	*	*	240	125	701
16	*	*	230	120	70	40
17	*	280	130	75	45	20
18	*	200	90	50	30	15
19	*	140	70	35	20	10
20	*	90	50	25	14	7
22	190	60	30	15	8	3
24	130	40	15	10	6	2
26	90	35	12	8	5	2
28	70	30	10	7	4	2
30	60	25	5	5	3	1

Based on composite of 0.5 percent maximum dry matter loss calculated on the basis of USDA research at Iowa State University; Transactions of ASAE 3330337, 1972; and "Unheated Air Drying," Manitoba Agriculture Agdex 732-1, rev. 1986.

* Approximate allowable storage time exceeds 300 days.

Combination Drying

Combination drying is the most common method today because it allows the greatest efficiency and grain quality. Combination drying is a delayed-cooling method where you take the grain up to a very hot temperature (about 200 degrees) and then move it to a bin to cool it slowly with ambient air. 

Image obtained through Google Images

Dryeration
Dryeration is less commonly used, simply because it requires more steps. In dryeration, once the corn is hot from the dryer, its put into a dryeration bin where it sits hot for 4-12 hours. This is called "delayed cooling". The idea is that the longer you let if cool off by itself, the less energy it will take to cool it manually. After it's cooled it's moved into a different bin for storage. Throughout this process there's a ton of condensation while the corn is cooling. This is why the corn must be moved to a different bin for storage, or it would go bad and get moldy along the walls and top of the bin. 

Dryeration example: high-temperature dryer system with two tempering bins. Tempering bins are filled in alternating order, making sure hot grain has at least 4 hours of time to temper before exposure to cooling air. After the grain has tempered and cooled, it's transferred to a storage bin.

Information taken from:
 <http://www.ag.ndsu.edu/extension-aben/documents/Corn_Drying_and_Storage_Tips_for_2011.pdf>
<https://store.extension.iastate.edu/Product/pm2089k-pd>
<http://www.agriculture.com/crops/grain-handling-and-storage/grain-dryers/two-delayedcooling-methods_182-ar45128>