Corn, Zea mays L., is grown for many reasons including its use in food and industrial applications. Corn oil is one of many useful products derived from corn. Commercial processing plants utilizing conventional methods for extracting corn oil typically separate the corn seed into its component parts, e.g., endosperm, germ, tipcap, and pericarp, and then extract corn oil from the corn germ fraction.
Although the precise processing steps and types of equipment vary somewhat from plant to plant, commercial corn processing can be classified as either a wet milling or dry milling process. Overall, wet milling is a sophisticated process involving many steps. When isolating the corn oil fraction, corn seed is first steeped in a water/sulfur dioxide (SO.sub.2) mixture at an elevated temperature and then passed through degerminating mills to separate out the corn germ. The wet milled germ contains about 50% oil, which is then washed and dried.
Dry milling physically separates the germ and pericarp from the rest of the corn seed. Dry milling can include tempering the seed by adding water followed by drying, cooling, grinding, sifting and aspirating the seed. Degermination is accomplished using a Beall degerminator (.TM.), impact mills, granulators or other similar degerminating equipment. The oil content of dry milled germ ranges from about 18% to about 27% oil.
Corn oil is extracted from wet milled or dry milled germ using physical expellers, solvent extractors, or a combination of both. Wet milled germ typically undergoes a two-step extraction because complete oil extraction is often unattainable using a single extraction.
It is also conventional practice to condition corn germ before oil extraction by adding moisture and heating the germ to about 100.degree. C. Conditioning facilitates complete oil extraction. Heating corn seed or germ before or during the extraction, however, can detrimentally affect oil quality.
Corn oil extracted using wet milling methods has a dark color and requires additional processing to achieve a useful oil. Dry milling methods tend to produce a better quality oil. Nevertheless, both dry and wet milling processes have drawbacks that include high energy costs, expensive equipment, high maintenance costs, and variable oil quality. Other corn oil recovery methods have been attempted, but most have not proven to be commercially feasible. Thus, there exists a need for improved methods that alleviate one or more of the drawbacks associated with conventional corn oil recovery methods.