Things You Have To Consider Before Setting Up A Small Oil Mill Plant

Oil production industry has quite a long history. As early as cave period of human being, ancient laboring people found that oil can be obtained from vegetable seeds by exposure to the sun. According to the historians, more than 2000 years ago, flax was processed into fiber and oil separately by ancient Egyptians in the Nile Valley.

Edible Oil is daily necessity of our lives. Nowadays, although various brands of oil is well stocked in supermarket, but they are manufactured by large scale oil mill plant which has advanced equipment and perfect process. However, rural farmers and small business owners prefer to small oil mill plant, which need low investment but profitable, easy to change oil seed type and master the technique. Nothing can be more interesting than pressing their oilseed to healthy and genuine edible oil.

Before investing a small scale oil mill plant, you have to consider oil seed type, quality of pressed oil and cake, process and other factors. Though there are only a few of oil extraction methods, but coordination and technique among each process is in fact expertly varied. Therefore, it is need to learn and master similarity and characteristic of different kinds of oil seed and then choose a right process for better production result.

Determine a reasonable process

  • Different kinds of oilseed can be classified according to their general character, in this way    several typical choices are available. For example, most oil seed can be mechanically    compressed, while some need to be decorticated before extraction
  • Many oil or oilseed proteins have unique flavor adored by consumers. To maintain their original flavor and quality, we have to choose a right process. For example, sesame oil, fragrant peanut oil and cacao butter are processed by high temperature and are processed by compression instead of solvent extraction method. While the best way of extracting olive oil is cold pressing.
  • Consider oil seed resource and supply status. For example, if oil seed type need to change frequently, you have to select a process that fit for multi oil seed type, but equipment configuration is usually complicated. If oilseed type is single, simple process is encouraged considering small oil mill plant cost.
  • Other factors such as labor productive forces, power supply, and plant address need to think over too.


Cleaning refers to screening of oilseeds. During harvest, transport and storage process, different kinds of impurities get into oilseed inevitably. We have to minimize impurity content to ensure quality of pressed oil.

Impurities in oil seed can be divided into three types, they are organic, inorganic and oil bearing impurities. Organic impurities include stem leaf, shell, weed and food grain. Inorganic impurities contain dust, mud or sand, stone and metal. Oil bearing impurities involve moldy and unsound kernel, kernel damaged by disease and insect and foreign kernel. Most impurities in oil seed do not contain and yield any oil at all. What’s more, certain amount of oil is absorbed and is remained in cake, which will lead to oil loss. Mud, leaves, shells will darken color of pressed oil, increase sediment content, decrease oil quality and cause bad smell. Meanwhile by-product such as cake will be affected too.

During oil extraction process, hard impurities such as stone or metal chip will result in abrasion and damage, oil mill shaft is wound around easily by long fiber impurities such as grass or rope, flying dust will worsen working condition in workshop. Therefore, efficient cleaning and dust removing of oil seed before oil extraction will improve oil yield rate, increase quality of oil and cake, prolong service life of equipment and ensure safe production.

Based on physical difference between oil seed and impurities, such as grain size, specific gravity, surface condition, hardness, magnetism and gas dynamics, impurities can be cleaned off by vibration, magnetic or air separation. Mini oil mill plant investors can choose one or a combination of above mentioned methods for oil seed cleaning. The requirements are to remove impurities as thorough as possible, the pure the better. Cleaning process is expected to be simple, short and high efficient.


Decortication is an important process before oil extraction.of oil seeds with shell, such as peanut, cotton seed and sunflower seed. Requirement toward decortication is high hulling rate, low powder tendency and is convenient to separate shell from kernel.

Shell or cover of oil seed consist of cellulose and semi-cellulose, which contains little oil. Some kinds of oil seed have high shell content, even reach to more than 50%.  From below table we can find shell content of peanut come to 28%-32%, that’s why we have to use a peanut sheller machine. While most other oilseeds also have shell content more than 20% beside soybean and rape seed. Decortication is highly recommended in respect that

  1. Shell does not generate oil, but absorb oil and remain in cake, which decreases oil yield.
  2. Pigment in shell is transferred to crude oil during extraction that will darken color of crude oil and affect oil quality.
  3. Extracting oil from shelled seed result in high shell content but low protein, which decreases utility value of pressed cake
  4. Increase power consumption and abrasion of equipment
OilseedsKernel ContentShell ContentOil Content
Whole SeedKernelShell
Cotton seed45-6040-5514-2530-400.3-1
Sunflower seed45-6040-5522-3645-541-2
Camellia seed62-7822-3825-3338-53/
Castor seed70-8020-3040-4857-60/
Flax seed574335-40582.2
Rape seed821833-47//
Palm kernel2575/48/
Cocoa bean881250//
Kapok seed604020-2540/
Safflower seed505028-3355-651.5-2
Perilla seed683234//

Table 1: shell and oil content of different oilseeds


Seed are rolled into flakes from grain by the mechanical action. The purpose of flaking is to destroy cell tissue so as to increase contact surface area and shorten oil run out path, which speed up oil extraction.

Oil seed is composed of innumerous cell. Surface of cell is a kind of tough cell wall contains cellulose and semi cellulose, while oil and other substances are included in cell wall. To extract oil, cell wall and cell tissue must be broke, and that is what flaking works. The thinner oil seed is rolled, the more cell tissue is destroyed, and oil extraction effect is the better.

However, flaking step seems not mandatory if small oil mill plant adopt pressing method instead of solvent extraction. On the principle of simplifying process and reducing mini oil mill project cost, oil seed cell tissue can also be broke by pressure and heat effect in pressing process. Requirements toward flakes are thin and even, low powder content without oil leak.

Oil pressing

Oil pressing can be traced 5000 years ago in China, Egypt and India. In 1795, water press was invented by Bramah, who makes people to extract oil by hydraulic method in 1818-1824. Vaerius D. Anderson in 1900 invented expeller, which becomes main equipment of pressing oil until now.

The process of oil pressing is to squeeze oil from oil seed by mechanical force. During this process, main changes are physical, such as oilseed distortion, oil separation, frictional heating, and evaporation of water. But with the effect of temperature, moisture and microorganism, biochemical changes also occur.

1. Screw oil press

screw cold oil pressScrew oil press is comparatively advanced oil extraction equipment and is widely used in this world. Screw shaft is driven by pulley and decelerated by gear box, oil seed is then moved to cage by rotation of worms. Due to narrowing space in cage, friction between oil seed and worms create temperature. Under influence of temperature and pressure, oil seed are squeezed and crushed, then oil is separated and run out from clearances between cage bars, cake is also squeezed from cake outlet.

  • Rotation speed of worms

Low speed lead to lower production efficiency and longer pressing time. High speed makes shorter pressing time and higher production efficiency, but lower oil yield rate.

  • Cage bars

There are generally 16-24 cage bars and are fixed on inner wall in each cage. The more cage bars the more run out channels, and vice versa. If channels between cage bars are long and wide, oil will run out smoothly. But over wide will cause dreg run out, and decrease pressure in cage. Channels between cage bars are usually 0.2-0.3mm, sometimes 0.2-1mm. For high oil bearing seeds, channels are designed to be more and wider. Cage bar assembly is shown below.

  • Cake outlet

Size of inner clearance in cake outlet affects pressing pressure inside cage. Smaller clearance in cake outlet is good for pressure and oil yield rate. However over small clearance may cause burnt seed, broken screw shaft or oil seed block. Therefore, clearance of cake outlet is usually adjusted to 0.5-1mm. Conical degree of cake outlet is 3° to 10°.

2. Hydraulic oil press

Hydraulic olive oil press

Hydraulic oil press is a kind of oil extraction equipment which works on the principle of liquid static pressure transmission theory. It’s featured with simple structure, good quality cake, and low power consumption. But disadvantages are high oil residual in cake and low output and longer preparation time before oil extraction. Unlike continuous pressing of screw oil press, hydraulic press extracts oil in batch. Its operation include cooked flake wrapping, load, pressing, and off load. All these preparation takes 15%-25% time of total steps.

In terms of mechanical performance, hydraulic oil press will be replaced by screw oil press. But when comes to special oil seeds such as olive, hydraulic oil press is indispensable anyway.

Although screw type oil press apply to a wide range of oilseeds, but olive is excluded. Many scientists tried to improve this because screw oil press can work continuously, but they failed. Screw oil press does not work on rheology property of olive pulp at all.

Actually due to strong plasticity of olive pulp, material in cage can not generate any pressure and thus do not lead to any oil extraction. That’s why we have to extract olive oil by hydraulic oil press.

Oil Purification

Unrefined oil made by pressing, solvent extraction or other method is called crude oil. Crude oil usually contains solid impurities such as cake powder, mud or sand, grass fiber, metal chips. These impurities exist in oil in the form of suspended state, so they are called suspended impurities. Suspended impurities have bad effect on transportation, temporary storage and refinery of crude oil, hence must be removed from crude oil timely after oil extraction.

Settlement and filtering are main separation method of suspended impurities in crude oil. Considering cost and easy operation, the former one is more suitable for small oil mill plant.

1. Gravity settling

With the effect of gravity force, natural settling is the simplest and commonly used for debris separation. This method takes advantage of difference between oil and suspended impurities and suspended impurities settle down from oil in natural settling condition. Although simple, but this process is very slow, because it largely depends on property, density and temperature of suspended particle. In addition, contact of hot crude oil with air for a long time will cause bad influence.

2. Centrifugal settling

Different ingredients in crude oil have different density and they do not solvate with each other. With the centrifugal force generated by high speed rotation, liquid and suspended substance in pressed crude oil is separated.

After centrifugal force stopped, light purified oil run out first due to force of gravity, while heavy particles in crude oil are attached to inner wall of drum of centrifugal oil filter.

For small oil mill plant, centrifugal oil filter is highly recommended.

  1. Featured with fast oil separation, at least 20kg crude oil can be finished every 4 minutes
  2. No filtering cloth or screen is needed
  3. Separated oil is clean, can be consumed or sold directly.


With progress of society, oil has been indispensable of human lives. However, limited by traffic or local economy, large scale oil plant can not meet everyone’s requirement of oil consumption. Small oil mill plant has been becoming more and more popular. Investing in a small oil mill plant not only turn farmers’ oilseeds into fresh and healthy oil, but also bring generous profit.

However, on the principle of low investment but bigger economic returns, investors have to learn more related information, determine an optimal oil extraction process and buy most suitable oil mill machinery, so as to maximize profits.