A Great Bowl of Popcorn

High-quality popcorn and a high product yield require the right cooling and ventilation system during grain storage.

Figure 1. Tempered air was introduced into the bottom of the bin, and the high static blower on the air conditioning unit circulated the air throughout the bin.

What makes a great bowl of popcorn? Large kernels? Great taste? No unpopped kernels? Or maybe all of the above?

Today's consumers expect a high-quality, consistent product. Much of the quality depends on the grain received from the grain farmer, but a surprising amount of a consumer's satisfaction depends on how the product is stored. To produce a good bowl of popcorn, the popcorn grain must be maintained at the correct moisture content. Too much moisture and the corn will begin to mildew and deteriorate; not enough, and the corn will not pop correctly.

Popcorn grain has conventionally been stored in bins with fans to provide conventional aeration; however, this method has several drawbacks. Because the aeration fans use outside air, the temperature and humidity of the air being used depends on outside ambient conditions. Hot, humid air in the summer and cold, dry air in the winter are not conducive to the stable temperatures and relative humidity needed for best storage practices. As a result, the popcorn has a shorter storage life, more grain fracture, increased spoilage, unacceptable levels of insect infiltration, and a lower popping ratio.

Figure 2. To monitor for consistent temperature, probes were placed at different depths within the filled bin.

American Pop Corn Co., Sioux City, Iowa, home of Jolly Time Popcorn, decided that there had to be a better way. Jeff Naslund, American Pop Corn operations manager, approached Scott Brainard, cooling and dehumidification product manager for Temp-Air, Burnsville, Minn., for help with the company's bin problem. The solution for American Pop Corn required the design of a system that could deliver a 55^oF (13^oC) ambient temperature and 65 percent relative humidity inside the storage bins, resulting in a stored grain product with 13.5 percent moisture content. The system would be tested on a storage bin that was 30' in diameter, 25' tall, and contained 787,000 lb of yellow popping corn.

To meet the design criteria, Brainard decided to use a 30-ton industrial air conditioning unit, the THPAC-30 model, with 20 kW of electrical reheat. Tempered air was introduced into the bottom of the bin, and the high static blower on the air conditioning unit was able to circulate the air throughout the bin (figure 1). To monitor for consistent temperature, probes were placed at different depths within the filled bin (figure 2). The moisture content was determined by testing core samples taken from different depths within the bin. Prior to introducing the tempered air, Temp-Air determined through testing that the average temperature of the corn in the bin was 68.9^oF (20.5^oC), and the moisture content of the grain was 14.3 percent. After 96 hours of operation, the corn was at 55^oF, and the moisture content was at the optimum 13.5 percent (figure 3).

Figure 3. After 24 hours of operation, the average temperature of the corn in the bin reached 55^oF. When the corn was tested again after 96 hours, the 55^oF average temperature had been maintained.

What American Pop Corn liked most about the process was that the temperature and moisture content stayed consistent within the bin despite changes in ambient temperatures and relative humidity outside the bin. The end result was less fractured grain, virtually no spoilage and a higher popping ratio, which equated to a 7.5 percent yield increase for the grain stored in the bin using the Temp-Air equipment. According to the company, the popcorn product was more consistent and at a higher quality compared to popcorn stored using the aeration method. As a bonus, the lowered temperatures stopped insect activity within the bin and eliminated the need for fumigation.

A 30-ton industrial air conditioning unit delivers tempered air into the bottom of American Pop Corn Co.'s storage bins to carefully control the temperature and moisture content.

The system worked so well on the bin that American Popcorn also added a THPAC-30 to its microwave popcorn warehouse to keep its stored packaged microwave popcorn from deteriorating.