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Reducing pest infestations and improving grain quality using grain-cooling technology
by Vaughn Entwistle, Milling & Grain Magazine, UK
round 10 percent of all stored grain in developed countries is lost to insect pests, moulds and mycotoxins. In developing countries, this percentage soars to as high as 40 percent. Other losses come from grain shrinkage, which results from grain’s natural ‘respiration’, and loss of moisture content. And all of these problems are directly related to elevated temperatures.
Some like it hot
Just-harvested grain is usually at its highest temperature and moisture content when it is transferred into a silo. Grain is an effective insulator and will retain its warmth in a silo for many days. Even worse, grain temperature will actually rise after it enters storage, because harvested grain is alive and continues to “breathe,” and “sweat”, taking in oxygen while releasing carbon dioxide, heat and water vapour (and therefore weight). As heat rises through the silo, the air in the head space heats and cools each day, creating ideal conditions for condensation to form and moisten the grain on the top of the stack. The high moisture content of recently harvested grain, combined with elevated temperatures, provides the perfect environmental conditions for the growth of moulds, toxins, and breeding insect pests.
A chill wind
To counter this problem, many silos employ aeration, whereby a system of fans circulates air from the bottom to the top of a silo, blowing air through the grain and cooling it. Aeration not only reduces the propagation of insect pests in the grain (by lowering the temperature and humidity in a storage bin), but also preserves grain quality and even improves seed viability. Typically, aeration works by locating a number of centrifugal blowers around the base of a silo or grain bin. The correct timing of this process is so critical that aeration systems often employ a planned control program which aims to force maximum airflow through the grain bulk as soon as it enters storage to cool the kernels and prevent the grain from sweating and heating. When grain is first loaded into storage, the aeration fans may need to run continuously for the next one to three days until the so-called “heating front” moves from the bottom to the top of the grain and up into the head space. The goal is to flush all the hot humid air out of the
Image courtesy of ©Frigortec
86 | September 2018 - Milling and Grain