Miller Magazine Issue: 141 September 2021

77 ARTICLE MILLER / september 2021 and moisture content of grain increase. The consequence of heating by respiration is loss of grain weight. Respiration increases as heat increases. Water content rises as result of the oxidation of grain carbohydrates or fats. The water content will decrease the storage life of the grain by favor the infestation of bacteria, mites, insects and fungi. A grain cooler reduces the chances of grains being damaged during storage. Prevention of weevil development Weevils and other insects can damage stored grain and their activity and development is influenced by the temperature of the environment. Navarro (1975) shows that at temperature above 20 to 32 °C the development of the insects is in optimum. However temperature less than 10 to 15°C reduce the activity. Therefore the grain is protected when grain is chilled. The Figure 4 shows the details. Prevention of fungi Microorganisms such as fungi and bacteria adhere to the surface of the grain kernel (Mühlbauer, 2009). The development of fungi depends on the temperature, hu- midity and the grain’s moisture content (Lacey, 1980). Their growth is prevented in the storage facility by dry- ing and grain cooling. Therefore, it has to be considered that grain is biological active and there is a change over the time. This is certainly true when the respiration activity of the grain is high and water and heat arise. Then mois- ture content of the grain, its storage temperature and the relative humidity will lead to fungus growth. Thereby the danger of fungal contami- nation is not only the dete- rioration of the grain but the increase in mycotoxin which have toxic effects on humans and animals. Most mycotoxins are heat-stable can persist through grain processing. For this reason, the formation of toxins must be prevented by stopping harmful fungi (Ro- demann, 1999). Grain cooling can decrease damage from fungi and their mycotoxins as fungal growth doesn’t take place at low temperature even if grain’s moisture con- tent is above 14%. Extension of storage time The safe storage time of grains depends on the mois- ture content as well as on the storage temperature of the grain (Agena, 1961; Wimberly, 1983). The storage period timer in Figure 5 shows the estimated safe storage time for grain according to its temperature and moisture con- tent (Sontag, 2014). The safe storage time for any par- ticular condition of grain can be read by matching the grain’s moisture content against its actual temperature. The section of the line on the vertical axis of the storage period gives the possible safe storage time of the grain. It is obvious what grain cooling does for the extension of safe storage life of grains particularly in tropical environ- ments. The example shows that for a moisture content of 14.5% the safe storage life at 31°C is around 18 days while at 10°C it is increased to around 300 days. BENEFITS OF GRAIN COOLING FOR GRAIN DRYING PROCESS During the process of grain cooling the heat of the grain is removed and relative humidity of the air is lowered ac- cording to the psychromatic chart. Thus, the air can remove moisture from the grain in arrange of 0.5 to 2% moisture content depending on the moisture content of the grain (Boser, 1980). Even if the moisture reduction is limited it contributes to a necessary drying process of moist grain Fig 1: Application of grain cooler at vertical silo (FrigorTec, 2012)