Single-stage hot pressing
is the most versatile and most widely used oil seeds processing method. Hot-pressing is suitable for the treatment of seeds with a low oil content (soy), but also for highly oiled seeds (rapeseed, sunflower).
Description of single-stage hot pressing:
After cleaning and thermal treatment, the seeds are ground into thin flakes which makes them easier to heat and dry, significantly increasing their ability to release oil. The ground seeds continue to heaters, where the temperature is increased and humidity reduced. The pre-treated seeds allow for easier separation of oil during pressing. The advantage is lower investment costs, but the disadvantage is a lower oil yield.
Two-stage hot pressing
ensures the highest oil yield of all technologies. Pre-heating the seeds alters the properties of cell structures, converts proteins and aggregates oil at the cellular level. With increasing temperature the viscosity of the oil decreases significantly. These effects enhance the compressibility of oil.
Description of two-stage hot pressing:
The technology starts with a reservoir which ensures sufficient supply of seeds for several hours of running the pressing shop. The seeds are temperature-stabilized and ground into flakes. This phase can be equipped with technology for cleaning, weighing and shelling the seeds and separating husks.
Pre-treated seeds enter the first-stage heater, where they are heated and stripped of excess moisture at the optimum parameters for the first-stage pressing. The heated material is fed into the first-stage press. Oilcakes from the first stage are fed into the second-stage steam heater, where the oilcakes are reheated and the remaining moisture evaporated. The second-stage presses carry out the final pressing. The resulting oil contains particulate impurities (pre-press) and needs to be further processed by separation and filtration.