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September 25, 2018

The big chill – Reducing pest infestations and improving grain quality using grain-cooling technology

by Vaughn Entwistle, Features Editor, Milling & Grain Magazine, UK

Around 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 grain and quickly reduce the grain temperature from the mid 30s°C down to the low 20s°C. Automated aeration systems will then run the fans intermittently to keep and maintain the grain temperature as low as possible throughout the storage period.

After the aeration fans have been running continuously for two to three days, the fan run time may be reduced to nine to 12 hours per day for the next seven days. An initial reduction in grain temperature of 10°C ensures grain is less prone to damage and insect attack, while further cooling becomes a more precise task.


Read the full article in the Milling and Grain magazine online, HERE.
 

The Global Miller
This blog is maintained by The Global Miller staff and is supported by the magazine Milling and Grain
which is published by Perendale Publishers Limited.


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