Cereal, Oil and Plantation Processing

Edible oil processing

Crude oil obtained by mechanical expelling or solvent extraction contains non-glyceride impurities, and refining removes them in a fixed sequence. Each stage targets a specific class of impurity, so the stage names must be matched with what they remove.

• Degumming — removes phosphatides (phospholipids). These are hydratable: water or dilute phosphoric or citric acid is added so that the phosphatides swell and separate as insoluble gums, which are then removed by centrifugation. Example: a crude soybean oil treated with water and centrifuged loses its gums and is then ready for alkali refining. Degumming is therefore the stage paired with phosphatide removal, not with wax or pigment removal.

• Neutralization — removes free fatty acids (FFA). Alkali converts them into soaps that are separated from the oil, and it also carries down some residual gums.

• Bleaching — removes colour pigments and traces of oxidation products. Adsorbents such as activated clay or activated carbon take up these compounds from the oil before it is filtered.

• Winterization — removes waxes and high-melting glycerides. The oil is chilled slowly so that these components crystallize and are then filtered off. This is the stage that removes soft wax from the oil.

• Deodorization — removes volatile odour compounds by steam distillation under high vacuum. It is the final refining step.

• Hydrogenation — adds hydrogen across the double bonds of unsaturated fatty acids using a catalyst. The product is a saturated or partly saturated fat used for shortening and margarine base; hydrogenation is therefore associated with the production of shortening.

• Blanching — a brief heat treatment that inactivates enzymes such as lipoxygenase and peroxidase. It is an enzyme-inactivation step, not a dye-removal or oil-refining step.

• Leaching — solvent extraction of a soluble constituent from a solid matrix. It is a solid–liquid extraction, and in this context it refers to separating a colouring matter from plant material.

Expeller efficiency. The efficiency of an oil expeller is the pure oil recovered divided by the oil originally present in the seed. Pure oil recovered is the expelled oil mass multiplied by (1 − impurity fraction), since solid impurities must be subtracted first. For example, 50 kg of seed containing 40% oil yields 16 kg of expelled oil with 4% solid impurities. Then pure oil = 16 \times 0.96 = 15.36 kg, oil in seed = 50 \times 0.40 = 20 kg, and efficiency = \frac{15.36}{20} \times 100 = 76.8\%.

Paddy parboiling

Parboiling is a hydrothermal treatment of paddy performed before milling. The process has three steps: soaking the paddy in water, steaming it to gelatinize the starch in the endosperm, and drying it back to safe moisture. Because the grain is treated before husking, parboiling changes both the nutritional quality and the milling behaviour of the rice.

• Nutritional value — during soaking and steaming, water-soluble vitamins and minerals, particularly thiamine and other B-group vitamins, migrate from the bran layer into the endosperm. The milled parboiled rice therefore retains more nutrients than raw milled rice, so parboiling increases the nutritional value of rice.

• Head rice recovery — gelatinization hardens the kernel and makes it less prone to fissuring. Fewer grains break during husking and polishing, so the head rice recovery increases.

• Broken rice and milling losses — because the kernel is stronger, the broken rice percentage decreases and milling losses are reduced rather than increased.

• Gelatinized — describes starch granules that have absorbed water and swollen under heat, losing their crystalline order. Parboiling is the process that gelatinizes the starch of paddy.

Cereal milling equipment

Each cereal requires milling equipment designed for its kernel structure. Matching a machine to the correct grain is a standard identification point in cereal processing.

• Mist polisher — used in rice milling after whitening. It removes the remaining bran layer from the polished rice, with a fine water mist that helps the bran adhere to the rice surface and be removed.