Temperature fluctuations and moisture migration in wheat stored for 15 months in a metal silo in Canada

Temperatures and moisture contents inside a metal silo filled with 20 t of wheat were monitored from August 2003 to October 2004 in Western Canada. In the summer and then repeated in the autumn of 2005, grain moisture contents inside small columns, inserted in the top of the grain bulk in the same metal silo, were measured after 4 and 8 weeks. The columns had the following configurations: 1) both the top and bottom of the column were open; 2) the top of the column was open and the bottom was sealed; and 3) the top of the column was sealed and the bottom was open.During the 15-month period, headspace temperature averaged 2.9 ± 0.2 °C higher than that of the ambient air with a maximum of 18.3 °C and a minimum of 0 °C. There was larger temperature fluctuation in the headspace than inside the grain mass. The average temperature gradient was 5.09 ± 1.24 °C/m inside the grain mass. The highest temperature gradient was 32.4 °C/m and it was located at the center of the bin at 1.6 m high. “Inside” grain had a lower moisture change than the surface grain.Grain in the top section of the column with the column configuration of Top End Open had the largest change of its moisture content, and grain in the middle section of the column with any of the configurations did not change. Grain inside the small columns at different locations in the silo had different moisture movement trends. These trends were consistent with the measured moisture migration in the entire silo. These results confirm that even in a small silo there were temperature gradients large enough to drive air movement and the induced convection currents could cause moisture migration.