Crude Maize oil is extracted from corn germ by squeezing or steeping with solvent.
Corn oil processing technology
The production of corn oil generally includes 2 processes: germ separation and maize germ oil pressing.
Corn germ separation
The first step of corn oil processing is the separation of corn germ. There are 3 kinds of corn germ separation methods: dry method, wet method and half-wet (semi-wet) method.
- Dry method corn germ separation
That is, the corn does not carry on the water regulation procedure, but is directly processed by mechanical method of extrusion or impact to separate skin, the embryo and the endosperm. This technology is simple, energy consumption is low, and no pollution; but the efficiency of the extraction is low, and the embryo contains more endosperm.
- Wet method corn germ separation
This is a method that includes corn soaking, crushing, degerming, and separating germ from starch by rotary liquid separator. The germ separation efficiency can reach 85%~95%. As the water content of germ is as high as 60%, it must be dried. After drying process, its water content is 2%-4%, and oil content is as high as 44% ~50%. Therefore this wet method corn germ separation consumes higher energy and pollutant to environment. besides, its equipment investment and production cost are high, while the investment recovery period is long.
- Half-wet corn germ separation
The principle of this method uses the nature that of corn germ and endosperm have different water content and water-absorbing quality, and after water absorbing, they have diversity in elasticity, toughness and crushing strength, to choose suitable equipments for corn breaking, peeling and degerming. Then uses different physical characteristics of embryo and endosperm to press the germ flat, and crush the endosperm; after sifting, sort out germ, in order to achieve the purpose of germ extraction. This method tempers the corn till the water content reaches 16% to 20%, and then peel, crush and grind the corn to get corn germ. This embryo extracting efficiency can reach more than 85%, with low energy consumption, no pollution, less equipment investment, short payback period of investment and low production cost; but the embryo contains a certain amount of endosperm.
Corn oil production process
There are 2 ways to make oil from corn germ: one is pressing method, which is suitable for small to medium size oil mill plant; the second is solvent extraction method, which is suitable for large scale oil factory; the third is aqueous enzymatic method, which is a new method developed in recent years. There are only a few large enterprises that produce corn germ oil by adopting both pressing method and solvent extraction method. This corn oil processing technology combination can realize oil yield 97%
Corn germ pre-pressing process
Generally use screw oil press. To ensure higher oil yield, in addition to meet the above conditions, the pressure of corn oil press shall be above 69 MPa. After pressing, residual oil in the cake is controlled at 6% to 7%, and the moisture content of the cake is 3% ~ 4%. For safety reasons, the moisture content of the cake shall be adjusted to 12%.
Corn oil solvent extraction
The moisture content of the corn germ must be controlled in a proper range to meet later pre-pressing and solvent extraction process moisture requirements. At the same time, proper moisture content is also conducive to the corn germ flakes do not stick to the rolling stock, easy to make maize embryos pressed into uniform slices, and create favorable conditions to reduce residual oil in flakes. The suitable water content of the dried flakes is 10% ~ 11%. To prevent the powder of the flakes, the thickness should be controlled at 0.35 ~ 0.45mm. Steaming, pre-pressing and cooling can further change the internal and external structure of the germ particles, so that the protein can be frozen and modified to reduce the resistance of the oil molecules spread outward, at the same time adjust the moisture and temperature of the material. For the corn germ in pre-pressing &solvent extraction technology, the water requirement of the material shall be controlled at 4% ~ 6%. For 6# solvent oil, the temperature of the feeding corn germ flakes is better controlled at 50 ~ 55℃. The operation of the corn germ solvent extraction, purification, evaporation and solvent recovery is conducted as normal solvent extraction process.
Corn oil refining
Crude corn oil has deep amber color. It contains 1-3% phospholipids, >1% sterols, tocopherols or other unsaponifiables, 1.5% free fatty acid, 0.05% wax and unpleasant smell. Crude corn oil has high impurity content and gets turbid when temperature is low, so it cannot be used directly.