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A Review of Wet-milling Procedures. Proceedings of the Corn Utilization Conference V

Proceedings of the Corn Utilization Conference V.
National Corn Growers’ Association. St. Louis, MO.
Singh, S., L.A. Johnson, and S.R. Eckhoff. 1994.

The annual corn production in the United States now exceeds 236-million tons. The corn wet-milling industry is the second largest consumer, accounting for 16% of the annual crop on 1992. Although wet-milling plants have grown larger, now averaging over 3820 t/day capacity, the chemical and engineering processes and grain quality factors involved are not well understood. Interests in better milling hybrids and in hybrids with unique starch characteristics have been spurred by recent developments in biotechnology. Advances in improving wet-milling unit operations and identifying hybrids with unique properties are limited by the absence of widely accepted laboratory and pilot-plant wet-milling procedures. The present paper presents a review and comparison of laboratory and pilot-scale wet-milling procedures.

The commonly used laboratory and pilot plant wet-milling procedures differ substantially in the method of steeping, equipment used to grind the corn, method of starch/gluten separation, and method of fiber washing. The methods may be characterized by scale; namely single kernels (White et al, 1990), 100 g (Singh, 1994), 300-1500 g (Watson et al., 1951; Watson et al 1955; Eckhoff et al, 1993; Steinke et al, 1991) and 1-4 bu.

The first attempts at simulating wet milling in the laboratory were made by Zipf et al (1950) and Watson et al (1951). Zipf et al (1950) used a one-step steeping system in SO2 concentration. Watson et al (1951) also developed a static but countercurrent steeping procedure. Steinke et al (1991) used countercurrent steeping with recycling to closely simulate commercial practice. The more closely industrial practices are simulated the more representative the yields are of industry results. Some procedures use a Quaker City mill (Eckhoff et al, 1993) and others merely use food blenders (Steinke et al, 1991). The method of grinding seems to have little effect. Either centrifugation (Steinke et al, 1992) or starch tabling (Zipf, 1950; Watson et al, 1950; Eckhoff et al, 1993) is used to separate starch/gluten. Most believe starch tabling gives more reproducible results. Some use multiple tablings; but most use one step of tabling. Not all investigators use the same length and pitch of table; but most use a table about 20 ft long and 0.0094 pitch. Fiber is often separated and washed differently. The best results are achieved when separating into coarse and fine fiber fractions and when extensively washing the fiber.


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