Miller Magazine Issue: 120 December 2019

84 ARTICLE MILLER / DECEMBER 2019 In many grain-growing areas of the world the MC of grain at harvest is too high for safe storage. This damp grain is readily attacked by molds unless it is protected in some way. The most widely used method of preventing mold growth is to dry the grain to a safe level. Burrell (1982) ar- gued that there is a balance between “safe moisture con- tent” and “safe temperature”: The lower the temperature of bulk grain, the damper it can be safely stored. This leads to the conclusion that drying need not be so stringently ap- plied since the power required to evaporate moisture from a bulk of grain is far greater than that required to cool the same bulk. For example, the energy required to evaporate 6 percentage points of moisture from a grain mass is at least six times greater than that required to cool the same bulk from 25oC to 5oC by using refrigerated air. Therefore, chilled storage may have an economic advantage over drying. This advantage is even retained when storing ex- cessively damp grain, which requires frequent re-chilling, including the high capital investment costs for equipment. In the major study “Enhancing the Quality of U.S. Grain for International Trade” (U.S. Congress, 1989), the mainte- nance of low temperature and moisture levels in bulk-stored grain was identified as the primary way to preserve grain quality and prevent damage from molds and insects. Grain chilling is a technology that can be successfully applied un- der many climatic conditions to preserve grain quality dur- ing storage when commodity value and profit margins are sufficient. It permits the short- to long-term storage of grain independent of the ambient conditions. Grain chilling has been applied commercially in over 50 countries during the past 40 years but has only in 1994 gained recognition in the United States (Maier, 1994.( It is estimated that over 80 million tons of grain are cooled annually worldwide with grain-chilling systems. Grain chilling is accept- ed as a grain conditioning technology in much of Western Europe; currently most new units appear to be marketed in Southeast Asia. In the 1960s grain chillers were primarily used as a means of preserving high-moisture (moist, damp) grain. Later, grain chilling was applied to improving storability of sensitive commod- ities subject to development of heat foci (hot spots), i.e., for soybeans and maize, and preserving the quality of high-value dry grain, seeds, and edible beans, primarily against mites and insects (Navarro and Noyes, 2002). RECENT DEVELOPMENTS A significant aspect of effective aeration control is our ability to monitor the tempera- ture in the aerated silos. Similar to fumigation, O2 or CO2, temperature and humidity should be monitored to ensure a successful aeration. As a common practice temperature sensors have been installed to ensure timely cooling of grain in silos. Such monitoring is performed by techni- cal personnel on site at predetermined regular times, par- ticularly during aeration. The conventional method of such monitoring is the visit of the technical personnel on regular basis to monitor the changes in temperature. This method necessitates precious time and travel of the technical per- sonnel, which makes the monitoring expensive. Wireless sensors for monitoring temperature and rela- tive humidity have been developed to enable the technical personnel record the data (Fig. 2)(Centaur Analytics, 2018). Such development facilitates the analysis of the cooling pattern of the grain bulk without the presence of the tech- nical personnel on site. Since the aeration to cool the grain mass lasts many days and the aerated structures may be located at distant sites then the location of the operator, such development offers an excellent tool that can be in- Fig. 3 – User interface for monitoring and managing the aeration process of a stored commodity (automatically or manually). Specifically, the user may choose between “manual” or “automatic” mode (left side) while receiving information about the current weather and grain conditions (right side). For the “automatic” mode the user may set the target temperature or the target moisture content.