Drying Tough Wheat in 2008

Weather conditions across most of southern Ontario are just not making it easy or feasible to do much wheat harvesting. Just when the wheat is almost ready to go, the cumulous clouds start to form, the sky starts to darken and the rumble of thunder can be heard in the distance. Farmers know from experience that the longer ripe wheat stands in the field, the higher the chance for quality degradation. In an effort to minimize this risk, some producers will consider harvesting wheat that is tough and then at least it's off the field. If this is your plan make sure you are set up to deal with this tough wheat. You need the right equipment and the knowledge to make it work.

Natural Air and Low Temperature Drying

Natural air drying of wheat will only occur when the relative humidity of the outside air is below the equilibrium moisture content of the grain. Because of this, the effectiveness of natural air drying systems is greatly reduced during rainy periods, on humid days and at night when humidity levels are normally high. When air temperatures fall below 10oC, forced ambient air will not pickup as much moisture and supplemental heat may be required. Natural-air drying during extended periods of humid weather may require some additional heat. Raising the temperature of the incoming air by 5 Centigrade degrees will dry the air allowing drying to continue. Recommended airflows for natural-air and low-temperature wheat drying are listed in the table below.

Recommended airflow for natural-air and low-temperature wheat drying.

Caution: Just because the fan is running don't assume that it is moving air through the contents of the bin. If the static pressure under the aeration floor exceeds the capability of the fan, the fan is in a stall situation. This means that the fan is spinning, using energy, but it is just churning air. No air will actually be moving up through the grain mass. The only way to know what the fan is doing is to measure the static pressure under the aeration floor and determine the air output from the Fan Performance Curve.

In order to dry tough wheat, the fan should only be operated when relative humidity levels fall below 75 to 80%. The Equilibrium Moisture Content of winter wheat at 15oC air temperature and 75% R.H. is 14.7%, 20oC and 80% R.H. is 14.7%, 25oC and 80% R.H. is 14.4% and 30oC and 80% R.H. is 14.2%.

The wheat at the top of the bin will be the last to dry. Each day of fan operation will push a drying front up through the bin. This drying front may not reach the top of the bin that same day. Be sure to take your moisture samples at the same depth each time to know how the moisture content is changing over time, at that depth. Bins with stirrators will have fairly uniform moisture levels throughout the whole bin as a result of the mixing that has been done.

Heated air drying in a bin without stirrators, or some means of continuously removing the dry wheat from the bottom of the bin, will result in over-drying of the wheat at the bottom of the bin.

High Temperature Drying

With high temperature drying, large volumes of heated air, 40oC or higher are used to accomplish drying in a few hours or days. Corn dryers could be used but you might need to reduce the drying temperature to avoid loss of starch quality and germination. The baking quality of wheat is damaged if the temperature of the grain reaches 60oC for any significant length of time. For safe drying, the temperature of grain kernels should never exceed 60oC. When heated air dryers are used, it is a worthwhile precaution to have samples evaluated to ensure the dried grain meets market standards.

Maximum recommended air temperatures for drying milling wheat:

• Non-recirculating batch dryers 60oC
• Recirculating batch dryers 60 - 70oC
• Cross flow continuous dryers 60oC
• Parallel flow dryers 70oC
• Seed wheat 40oC

** Always check with your seed company or grain buyer as to acceptable or allowable drying
procedures.