Pretreatment and Pressing of Corn Oil Processing

Description of corn oil processing technology

High oil corn is used for oil extraction, which includes the separation of embryo and oil extraction of embryo. The separation methods of maize embryo include dry desquamation and wet grinding. Raw materials are not treated by moisturizing water directly desquamation embryo production powder, also known as dry desquamation embryo production powder. Generally, it can be used when the moisture content of grains is around 18%, but the processing loss is great. The wet grinding method is used to prepare the embryo powder.

Corn oil production process

In the process of producing grits, corn starch or corn starch sugar, about 8% to 12% corn germ can be recovered, which can be used to make corn germ oil and corn germ protein. Corn germ oil can not only be refined into salad oil, margarine and other nutritious edible oil, but also is the raw material of pigment, paint and soap industry. The deoiled cake contains rich nutrients such as protein and can be used as a nutritional supplement for many kinds of food.

The process, equipment and operation of oil making from corn germ are basically the same as that of other oil, which must be cleaned, dried, softened, flaked, steamed and stir-fried, extracted and refined.

  1. Clean.Grits are made from reclaimed corn germ, which is mixed with more corn flour, crushed powder and dandruff. Sievemesh, clear the first level of clutter, 1. 5 the x1. 5 mesh/cm²; The second layer is used to remove corn flour, grits and dandruff. If there is still a large amount of germplasm in the sieve, 5×5 mesh/cm² or 7×7 mesh/cm² screen can be used to reduce the loss of corn germ. Corn germ from which cornstarch is regenerated, mixed with other impurities such as dander and coleoptile, needs to be rinsed with water several times in a shallow dish or in a flow groove.
  2. Dry.The corn germ recovered from grits and cornstarch contains high moisture after cleaning, and the enzyme is highly active and easily contaminated by microorganisms, resulting in oil deterioration and rancidity, which not only affects the output and quality of oil products, but also reduces the use value of the cake. To maintain the freshness of corn germ in storage and transportation, the cleaned corn germ must be dried or dried to a moisture content of less than 10%.
  3. Soften.The first stage of preparing oil for corn germ. In this process, the water content of corn germ is reduced to less than 10% while being treated with heat, which makes the material embryo undergo plastic changes. Softener is usually used in hot air dryer or hot steam roller dryer. When the material embryo softens, the temperature should not rise too fast, so as to prevent the premature protein denaturation and make the material embryo lose its elasticity.
  4. Flake.After softening the corn germ, it was rolled into 3-0.4mm thin slice by roller mil which promotes the destruction of cell structure, shortens the oil path, and facilitates the steaming and frying of the material embryo.
  5. Cook.The embryo into the steaming and frying equipment evaporate and the moisture content of not less than 12%, heating by 40-50 minutes, finally make embryo temperature over 100 °C, material moisture content of embryo gradually reduce from 12% to 3% – 4%, with material embryo color gradually changed to brownish red, and can not anxious burnt smell.
  6. Press.Methods of oil preparation include pressing, extraction and water substitution. The press method can be divided into wood, screw and hydraulic press according to the equipment and production scale. Because the production of corn germ oil is mostly carried out by small scale and auxiliary workshop, spiral oil extraction machine is most suitable.
    The type of machine can be determined according to the production scale, the scale of the larger production factory, can choose the 200 screw oil extraction machine assembled with the steam and stir-frying equipment, this machine has both the steam and stir-frying, the operation is continuous, the operation is simple, the material embryo steam and stir-frying, the oil extraction is completed in one time in a group of equipment.

When steaming and frying, material temperature of 115-120 °C, water content is 2% – 4%, squeezed oil directly into the press. Needs to keep 30-40°C at room temperature, initial into less volume of the whole embryo, after being squeezed machine normal operation, press the chamber temperature rise, then increase to the standard feed rate, and maintain even into materials, oil, and the loaves of bread, to smell good of the cake, pie slice solid, smooth surface, has a crack on the back, give oil to normal. If the temperature of steaming and stir-frying is low, the moisture content of the material embryo is relatively high, and the cake slices are fluffy, the moisture is very thick, the oil color is not correct, the hair is white and foaming, and the oil output is reduced. If the steaming and frying temperature is too high and the moisture content of the raw material embryo is too low, then the cake color is too dark, the smoke and caramel are emitted and the oil color is dark, and the oil output is also reduced. In the press machine with normal operation, the speed of oil extraction is normally controlled at 8 revolutions/min, and the pressing time of the blank in the press chamber is 2. 5min, the thickness of the pie slices is 5-6mm. The yield of maize germ from grits was 22% — 26%. The yield of corn germ from starch was 25% – 28% and 5% – 6%.

The unrefined corn germ oil, commonly known as “wool oil”, its moisture and volatile substances are 0.3%, impurity is 0.2%, acid value is 6%, sediment is 6% , pale yellow, smell is normal, through 280 °C heating, sediment precipitation. “Wool oil” is not resistant to storage due to its high moisture and impurity content. It needs to be refined through hydration, alkali refining and deodorization to obtain high quality refined corn oil.


Corn germ oil and refined corn oil are extracted by means of pressing. In particular, it is necessary to pay attention to all the key processing steps before corn germ is pressed and to oil road dredge and wool oil recovery in the process of pressing, which can effectively improve the ratio of grain and oil. Hair oil produced contains a certain amount of saturated fatty acids, lipids, waxes and cholesterol. Non-glycerine impurities such as free fatty acids, phospholipids, pigments and a small amount of protein colloids. There is also some pigment.

Therefore, in order to get refined corn oil, it must be processed by dewaxing, deacidification, decolorization and deodorization.

Two kinds of pigments in corn oil

One is natural pigment, such as carotene, lutein, chlorophyll and other substances, easy to be bleached soil adsorption decolorization. Another kind of pigment is the organic decomposition product, which is brown and dark brown. They are usually distributed in a positive gel state in the oil. Although some of the pigment is removed during processing, but a greater extent of recovery. The decolorization process used to make corn oil generally is; cross decolorization technology of secondary decolorization of primary bleaching soil; to the material embryo processing is not timely, the production oil color is darker wool oil, decolorization is more difficult, then may use the predecolorization. In addition to the original corn flavor, the decolorized corn oil also has the “soap” flavor in alkali refining and the “earth fishy” flavor in decolorization.

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