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Factors Affecting Expansion of Corn Meals with Poor and Good Expansion Properties¹

¹Contribution 97-59-J from the Kansas Agricultural Experiment Station, Manhattan, KS. ²Graduate research assistant and professor, respectively, Department of Grain Science and Industry, Kansas State University, Manhattan 66506. ³Present address: Earth Grains Inc., 4649 LeBourget, St. Louis, MO 63134. ⁴Present address: R&R Research Services Inc., 8831 Quail Lane, Manhattan, KS 66502. ⁵Corresponding author. E-mail: r_and_r@kansas.net

Two corn meals, one with good and one with poor expansion properties, were used to study the critical factors responsible for poor expansion during corn curl extrusion. Screening tests revealed that the corn meal with poor expansion had a slightly larger particle size. This sample also had a larger proportion of opaque particles compared to the corn meal with good expansion. Extrusion of coarse corn grits showed that larger particle size alone could cause poor expansion. Water diffusion tests showed that the sample containing more opaque particles was more competitive for water. As a result, in corn that contained both opaque and vitreous particles less water was available to the vitreous particles. The underplastisized (dry) vitreous particles remained glassy (unmelted) during extrusion, resulting in reduced expansion of the extrudates. The results suggest that addition of water to the conditioning cylinder of the extruder would overcome poor expansion.