[2] In the main agricultural countries, drying comprises the reduction of moisture from about 17-30% w/w(water personne weight) to values between 8 and 15%w/w, depending on the grain.
However, low temperatures in storage are also highly recommended to avoid degradative reactions and, especially, the growth of insects and mites.
They normally consist of a bin, with heated air flowing horizontally from an internal cylinder through an inner perforated metal sheet, then through an annular grain bed, some 0.50 m thick (coaxial with the internal cylinder) in radial direction, and finally across the outer perforated metal sheet, before being discharged to the atmosphere.
[3] It is possible for long period safe storage if grain moisture content is less than 14%, and stored away from insects, rodents and birds.
The low relative humidity means air is dry and it has a large potential of picking up water.
In general, one-half reduce in relative humidity is caused by 20 °F degree increase in air temperature.
[10] Low-temperature drying process usually takes 5 days to several months depends on several important variables: weather, airflow, initial moisture content and amount of heat used.
The advantages of in-storage low temperature drying are quick filling, high quality product, less equipment requirement; while the disadvantages are long drying time, electrical demand if using electric heat, high management skills and uncertain harvest moisture content.
Compared to low-temperature methods, multiple-layer drying requires higher temperatures, which results in a shorter allowable storage time.
Usually, the temperature rise after the LP burner is remained low in order to avoid over drying in the bottom layers in the bin.
Moreover, using stirring system can avoid over drying in bottom layer problem and give a uniform grain moisture content in the whole bin.
When drying is complete, the burner is turned off while the fan and stirrer are used to mix the corn to achieve equal moisture content and temperature.
When the drying process is completed, grain is put in the regular bin floor, thus unloading time is reduced.
The column formed in this kind of dryer is made up of two vertical perforated steel sheets, which is about 12 inches thick each.
The advantages of column batch, stationary bed dryer are easy to move and the dyer can be used as cooler; while the disadvantages are time losing when cooling, loading and unloading and unequal moisture distribution when drying is completed.
When column batch recirculating dryer is used, the moisture content variation problem is avoided, but the additional handling process may result in grain spoilage.
In reality, the lower the airflow rate, the higher the grain moisture content variation between two sides of the column.
What's more, high temperature may not have adverse effect on sunflowers kernel, which may be the reason of the fatty acid composition.
The seed coat of bean is quite fragile and easy to damaged in cracking and splitting, which may cause loss to the producer.
Some studies on beans suggested that in order to avoid cracking, it is better to keep drying air above 40 percent relative humidity.
The major problem that occurs from high temperature drying and then rapid cooling of the grain is stress-cracking.
Stress-cracked kernels often absorb water too quickly, are more likely to become broken, and are increasingly susceptible to insect and mold damage during dry storage.
Its advent was necessary for the advent of ubiquitous combine harvesting in all regions, even humid ones and higher-latitude cooler ones, as combining involves no time interval between reaping and threshing, unlike traditional harvesting of cereal grains, which involved shocking (stooking) the grain and allowing it to air dry for weeks in an intermediate step before threshing.
As recently as the 1930s, when Cyrus McCormick III wrote his seminal history of the mechanization of grain harvesting (The Century of the Reaper), the mechanical prowess of combine design had already become substantially advanced, but the moisture of the grain still represented a great barrier to extending combining to ubiquity.
The general sweep of advancement of mechanized bulk materials handling that occurred in the mid-20th century was of a piece with these other interrelated aspects of novel systems, including greatly advanced trucking, power farming equipment, roadbuilding, electrification, distribution infrastructure for LPG and fuel oil, and so on.
All of these factors acting in concert were necessary to make possible the era in which humans produce grain in affordable abundance with extensive mechanization and very little labor per ton.