Corn processing has the highest worldwide production of any crop. The three main uses of processed corn are for animal feed, human consumption, and Ethanol production. US annual production of corn in 2016 reached 15.2 billion bushels or about 840 billion pounds. About 35% of US corn production went to the production of Ethanol, another 30% for animal feed products, and the remaining went for human consumption and export.
Corn has many uses in both food and industrial applications. The resultant processing of corn yields four basic compounds: starch, protein, oil, and fiber. The subject of starch and its uses will be discussed in part 2 of the Food Processing Webinar series.
In the production of various corn products for human consumption, there are two processes: a dry milling process and a wet milling process.
In the dry process, corn is cleaned and then hammer milled to a medium ground corn meal. The corn is mixed with water to make slurry, which is PH and temperature controlled. Enzymes are added to initiate a hydrolysis process to turn the corn starch into dextrin. This process is known as liquefaction. After liquefaction is complete, the “corn mash” is cooked to kill bacteria. The next step is fermentation, followed by drying and final milling.
In the wet process, corn is cleaned and then loaded into tanks for the steeping process, where it is soaked in a temperature-controlled dilute solution for up to two days. The result is the softening of the corn kernels and the absorption of the soluble nutrients. The germ is then removed, and the liquid is wet milled. The next part of the process is drying and the final stage is milling.
Another variation of “Wet Milling” is called Nixtamalization, where the corn is cooked in water and Calcium Oxide. This alkali process improves flavor and starch gelatinization. The mixture is then dried and milled into flour called Harina Massa. Harina Massa is the prime ingredient in corn flour tortillas.
Corn Flour is used in the production of snack foods like corn chips and tortillas.
The dried corn flour is volumetrically fed to a mill for size reduction. Final particle size is determined by the type of impact hammer, the speed of the rotor, and the size of the opening in the screen in the bottom of the grinding chamber. Air is used to convey the milled material to a process collector, where the product is separated from the air stream. A typical corn flour grind on a Mikro Pulverizer is 97% < 50 mesh or 300 microns. Corn meal can also be ground finer on a Mikro Pulverizer. A finer particle size of 98% < 100 mesh or 150 microns is also possible. The Mikro-Pulverizer can also be used for the wet milling process with a different system configuration.
Corn is an organic material, and therefore has a potential for explosion. As with all organic materials, the system must be designed to safely handle the potential for a dust explosion. System protection can be obtained by incorporating any of the following basic design possibilities:
- Designing the entire system for over-pressure and containment of the explosion as shown in this picture
- Venting of the system to safely relieve the over-pressure
- Operation under an inert atmosphere to remove the explosion potential
- Utilizing a suppression system to quench the explosion before it propagates