Store it Damp, Keep it Cold
By Ralph Brown, University of Guelph


Two groups of farmers - in Eastern Ontario near Ottawa, and Western Ontario near London have been part of OCPA-sponsored trials to evaluate on-farm storage of damp corn for delivery to Casco Inc. Compared to conventional heated-air drying and storage at 15 per cent moisture, damp storage gives producers several benefits, including reduced energy costs and better corn quality (i.e., no stress cracks or heat-damaged kernels). In addition, it can simplify their operations if drying is not required, or it can increase flexibility because drying can be postponed if inconvenient. For wet millers such as Casco Inc., using damp corn may also lead to improved process efficiency and product quality.

The project, coordinated by University of Guelph researchers Dr. Ralph Brown and Ken Bennett, has demonstrated that corn can be stored at 18-21 per cent moisture for up to six months, as long as its managed correctly. The secret to success is using programmed aeration with cold night air to cool the corn to near-freezing temperatures. Bins used for damp corn storage should have full-floor aeration and temperature-sensing cables for periodic monitoring. Corn for damp storage should not be harvested until the end of the season, otherwise night time temperatures may be too high to keep it cool.

In 1998-99, the first year of the study, six producers in eastern Ontario delivered more than 1,300 tonnes of damp corn to Casco at Cardinal. Corn moisture content varied from 19-21 per cent among the farms at harvest and at delivery the moisture ranged from 17-19 per cent. Laboratory-scale milling quality of the damp corn was very good, with damp corn showing significantly better starch yield and quality than the same corn dried to 15 per cent moisture using an air temperature of 100oC. Although Casco reported no difficulties in milling the damp corn at Cardinal, the test runs were not large enough to demonstrate whether starch recovery and yield were any better than for dried corn at the plant scale. Consequently, two separate trials were planned for 1999/2000: a follow up study in eastern Ontario with 8,000 tonnes of damp corn, and a storage feasibility study in the warmer southwestern part of the province, with about 1,300 tonnes for delivery to Casco (London).

Unusual weather conditions in Ontario again in 1999 meant that there was not enough damp corn stored in eastern Ontario to evaluate full-scale milling at Cardinal. In the southwest, no storage problems were encountered and top quality damp corn was delivered to London in March. Unfortunately, operational problems in London when the corn was delivered prevented the assessment of milling performance on a plant scale for a second year. Nevertheless, the three trials have demonstrated the feasibility of on-farm storage of damp corn, and have given the researchers experience in managing the system. Farmers, as well, require a transition period as the operational logic is opposite to that of ambient air drying.

In 1998/99, grain temperatures in the bins were monitored automatically, and the cooperating producers controlled their aeration fans manually. Last year, prototype aeration controllers designed by the Guelph team were installed on several bins to automate fan operation. The controller monitored the temperature inside the bin and compared it to the ambient temperature outside. If the temperature difference represented a strong chilling condition, then the aeration fans were automatically turned on. The advantage of this type of controller was its ability to track the grain temperature in the bin as the corn cooled, and change the on/off setpoints accordingly. In this way, operation of the fan occurred only during colder conditions, down to a minimum temperature. After that minimum temperature was achieved, the aeration fans were only started periodically to offset spells of warm weather.

The controllers proved to be more energy efficient than manual operation of the fans, and made the system much easier to manage. Figure 1 shows the average grain temperature and aeration fan operation for a damp corn bin from loading in October until shipment in mid-February (although the low holding temperature indicates damp corn could be stored longer if necessary). There were 27 automatic aeration cycles, representing 243 total fan-hours of winter operation. For this bin, a 1.5-horsepower fan aerated about 5,000 bu of corn. The operational cost worked out to less than 1 cent/bu for an electrical energy cost of 10 cents per kilowatt hour. This could be reduced even further, as the cooling constraints were fairly stringent to ensure success. This year the controllers will be set to operate at fewer and more optimum times, and the minimum corn temperature setpoint will be increased to -5oC.

Damp corn storage with automatic chilling is a flexible and efficient way to handle late-harvested corn. It also has advantages for processors because undried corn has top quality for milling. However, the future of damp corn storage will depend on the willingness of the industrial corn market to change its buying methods in order to take advantage of that quality. The current basis of trade penalizes farmers for selling corn above 15 per cent moisture, so there is no economic incentive for producers who already have their own drying facilities.

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