STORAGE
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The preservation of grains through cooling systems
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by Noemi Reyes, Consergra, S.L.
roducts such as grains, seeds, oilseeds, nuts, and others that are similar are still alive when stored after being harvested. Their vital activity consumes their own mass and oxygen, generating carbon dioxide, water and heat. These create a multitude of well-known troubles such as stored product weight loss and quality decrease. Insect infestation is a particular problem in poorly stored grains. Insects eat and infect the stored product, which is also reheated due to their vital activity. Insects start their presence from 13°C and up, although the real insect infestation occurs from 18°C and up with a peak between 30°C and 40°C for most insect species. Mould presence and subsequently dangerous toxins, some of them carcinogenic, may enter into the food chain. When using chilled storage most of the micro-flora growth stays under control, since most micro-flora species develop at temperatures between 20°C and 40°C. In addition, water condensation appears inside silos and warehouses making grains stick to the internal silo/warehouse wall and rot. In the case of grains with a high oil or fat content, their quality decreases quickly due to the fat oxidation. Heat speeds up this unwanted process. Some products like rice, change flavour and colour under inadequate storage conditions. For example, rice changes its color from white to yellowish, and later to orange. Color change is a clear indication of product damage during storage, and its market price drops a lot.
84 | August 2017 - Milling and Grain
The evidence
Graph 1 shows different the effects of storing a product (in the case, the shown graph is suitable for wheat, barley and corn) under different conditions of temperature and water content. From the graph it is evident that a high product temperature, or moisture, or both, will damage the grain irreversibly. Table 1 shows the weight loss that typically occurs during any grain storage depending on different grain conditions. In just three months, the weight loss may reach the three percent of all storage. Quality loss occurs as well, although it’s not accounted for in the table.
Solving storage issues
Traditional methods trying to solve these issues include natural aeration. In cold weather, ambient aeration is an excellent