Vegetable oil is made from seeds of the oil-bearing crops, such as sunflower, corn, soya, safflower, cotton etc. The quality of oil, first of all, depends on the seeds quality. Oil seeds should have a sufficient oil content, their moisture not to exceed 6 % (otherwise the oil would appear to be too aqueous), and it also depends on maturation degree of the seeds that should have enough light and heat. Empirically it is quite clear that the higher oil content in seeds, the higher oil yield shall be.
The “cold” oil pressing method is one of the processes the vegetable oil is produced. Choosing of this method gives less oil yield as a result, however the cold oil pressing method, or so-called “extra virgin” ensures all useful elements and vitamins are retained in the final product.
Equipment used for the vegetable oil production by the cold pressing method
The cold oil pressing method requires less high-value equipment comparing to the other processes of oil production. This technology requires a screw-type oil mill that must include an oil press.
They are available of various types. The difference is that of tonnage capacities of the product to be processes, of the oil content in the oilcake tablets, and of the power consumption. As to the low-capacity oil mills (oil press mill) it is useful to choose a worm mill as simple as possible, which is capable, for example, of processing about 6-10 tons of the product per day. For large oil mills it is recommended to choose the oil pressing plant of a high output.
Features of the oil mills designed for cold pressing:
- the pressing is done at low temperatures only. The product is extracted by the worm press and extracting box (cage) unit. The oil produced is filtered from the sediment;
- pressing at lower temperatures prevents the protein from lysing; the initial expenses for the cold press start-up are considerably lower;
- when processing the product no contact is required with such substances as acids, alkali, solvents and other chemicals. The finish sunflower-seed oil produced by cold press is valued highly because it practically does not lose the consumer utility, i.e. vitamins.
Vegetable oil production technology by cold pressing method
It is worth mentioning, that it is the most harmless and environment-friendly process. But at the same time it is less profitable as provides less sunflower-seed oil yield in comparison with other technologies (extraction).
Before processing the sunflower seeds shall be prepared in the proper manner. The seeds must be cleaned carefully; the rate of contaminants should not exceed 1 %, and that of improper seeds not to be higher than 3 %.
Just before conveying the seeds to the oil mill, they need to be dried and decorticated (the seed hulls to be separated from kernels). Then the seeds are to be ground. The produced substance is called the oil seed meal.
Then the oil seed meal is charged to the oil mill where a liquid part — oil, and a solid part — oilcake are separated by the worm press. The pressing occurs due to movements of the oil seed meal in the press chamber (cage).The product is heated because of friction. As this process requires no heating, the final product is abundant with such substances as antioxidants, vitamins, and lecithin.
After processing the oil is drained into the crude oil tank and leaved for several hours to settle, or fed directly to the filtration area, where mechanical impurities are removed from the oil. The refined oil is poured into special barrels, only after that it goes for packaging. At present the technology of cold press is regarded as the most optimal, useful, and practical.
The oilcake remained after the sunflower-seed oil production may be used for extraction, secondary pressing with or without heating, or as the feed for livestock.
A disadvantage of the process is that the oil produced by the cold press has a short shelf life. To avoid this, the product shall be subject to refining.
Completeness of the oil pressing depends on certain factors, as follows:
- pressure force of the worm inside the extracting cage;
- thickness of the oil seed meal layer;
- density and viscosity of the product;
- the time of the product presence in the pressing cage.
This method of production requires the best sunflower seeds, carefulness and exactness of the personnel resulting in high performance and finish product of top-quality.
Sunflower-seed oil, the first oil press, or so-called “crude” oil, because after processing this is just settled and filtered. The product is characterized by not only set of useful substances contained, but it has surprising taste, excellent and attractive appearance.