Peanut Oil Introduction
Peanut oil (groundnut oil), as a kind of light yellow transparent edible oil with a pleasant fragrance and good taste, is relatively easy to digest. Peanut oil contains more than 80% unsaturated fatty acids (including 41.2% oleic acid and 37.6% linoleic acid). Besides, there are also palmitic acid, stearic acid, and other saturated fatty acids which cover 19.9%. The fatty acid composition of peanut oil is relatively good, therefore it is easy for human bodies to digest and absorb. Thus peanut oil production industry is a large and highly developed business.
Peanut Oil Pressing Methods
Generally, the husk content of peanut is 30-35%, and the oil content in peanut kernel is 40-50%. Therefore, the peanut pretreatment processes include cleaning, dehusking and separating of hull & kernels. According to pressing temperature, there are two peanut oil pressing technologies: hot pressing and cold pressing.
Processing Steps of Peanut Oil Production Line
There are impurities in peanuts before processing. First, a vibrating screen is needed here to remove the impurities from peanut. After screening, the impurity content is no more than 0.5%, and the peanut kernel content in removed materials is no more than 1%. Then the stone is separated from peanut by a destoning machine.
After husking, it is required that there are no hulls in the peanut kernels, or the hull content is < 2%-4%. And the peanut kernel content in hulls is < 0.5%.
Peanut sheller is consist of rack, fan, rotor, single-phase motor, screen, hopper, vibrating screen, triangular belt-wheel and drive belt. When the peanut sheller works, the peanuts are delivered into the hopper quantitatively, uniformly and continuously. Under the repeated strike, friction and collision of the rotor, the peanut hulls are broken. Then the peanut kernels and broken hulls pass through the sieve in a certain hole diameter (the sieve of big hole diameter for first shelling, and small hole diameter for second cleaning). Under the blow force of rotating fan, the peanut husks in lightweight are blown outside, and the peanut kernels pass through the sieve to achieve the cleaning effect.
The purpose of this process is to crush the peanut into a certain granularity, which can meet the condition for flaking. After crushing, the surface area of peanut is increased, better for the transfer of temperature and moisture when softening. The peanut crushing machine is mainly the toothed cracking roll.
When toothed cracking roll works, the upper layer roller chute can crush the peanut kernel into 3-4 pieces, and the lower layer roller can crush the kernels into the half.
The peanut kernel is soft, normally it does not need to be softened. Sometimes it can be flaked directly only after the suitable heat treatment. Please pay attention to the flake thickness (<0.5mm) when hot pressing, and avoid roller sticking when flaking.
Generally, cooking is adjusted according to the conditions required for hot pressing. When the moisture content is close to 1-2% and the temperature reaches 120-130℃, it is time to finish cooking and begin to press. It is better when the flake is in deep yellow and slightly oily. The cooking process influences directly on the smooth press, oil rate, and oil cake quality.
Peanut Oil Pressing
The peanut pressing processes can be divided into three stages, which are feeding stage, main pressing stage, and cake forming stage. The most common peanut oil pressing machine is the screw oil press.
Peanuts begin to be squeezed in this process, the air and little water are discharged, which make peanuts plastic deformation and begin to press the oil.
Main pressing stage
In this stage, high pressure is produced and lots of oil is discharged. The volume of pressing barrel is decreased rapidly and regularly, then the peanut is compacted strongly and particles are combined. Peanuts in pressing barrel become porous, then lots of oil is discharged.
Cake forming stage
Peanuts become tile-shaped cake in this stage and nearly propelled in integral type, thus producing great compression resistance. At this time, the tile-shaped cake has little compressibility, but the pressure still needs to keep high, so as to drain off the oil without absorbing back. Finally, the discharged cake is enlarged in volume because of the elastic expansion.
Hot Pressing VS Cold Pressing of Peanut Oil Production
Hot pressing is the traditional method of pressing peanut oil. With a high rate of oil output, good taste, and convenient storage, it is popular for home use. But because of the high production temperature, the peanut protein is usually severely denatured and lose plenty of nutrients.
Cold pressing technology is often applied in large peanut oil production plant. The production temperature is conducted under 60℃, which is beneficial to preserve the nutrients and comprehensively utilize peanut protein in peanut oil. The disadvantage is low oil yield, not suitable for small oil plant.