Although the screw press is the core element in any pressing plant, it has to be complemented by appropriate seed preparation to show its full potential. A low milling error - an index to describe the availability of the oil for solvent extraction - is the key to success, particularly in pre-pressing and solvent extraction plants.

A milling defect test measures the degree of cellular disruption in the seed. A low milling defect indicates substantial cellular disruption and enables greater solvent extraction efficiency. It is also a measure of how effectively the seed has been prepared.

A high milling defect is a result of improper seed preparation. No matter how efficient your pressing and solvent extraction processes, a successful result cannot be obtained if preparatory processes - cleaning, cracking, dehulling, flaking and conditioning - are not carried out properly. For better efficiency, a typical milling defect should be in the range of 0.2 – 0.3%. Preparation constitutes the basis of successful solvent extraction, and it is essential to have quality equipment to deliver a successful result.

Here are some remedial measures to address a high milling defect.

Cracking: Oilseeds need to be subjected to good cracking to make the dehulling process more efficient. There are different types of cracking strategies for different kinds of seeds - soybeans are cracked using roller crushers while sunflower seeds are crushed by impact. It is also important to keep dust formation to a minimum during cracking.

Kumar's Crackers are well constructed, efficient, and very low maintenance.


Cooking is an essential step in the seed preparation continuum. Cooking helps to rupture oil cells by flushing out intrinsic moisture, decreases oil viscosity, makes it easy to remove oil, coagulates protein in meal, and sterilizes the seeds by destroying enzyme activity and preventing mould and bacteria growth.

A portion of the seed's moisture migrates to the surface during this process, making the seed moist and softening the kernel. It reduces the load on the flaker and enables flaking with very few fines, and ensures stability during the extraction process.

Kumar's Cookers are vertical, multistage units with an arrangement for indirect steam heating. The gates of each compartment are operated by level systems that automatically control the flow of material and maintain the level in each stage. They comprise a central shaft driven by a gearbox with agitator blades to ensure a good mix. Homogenous treatment of the material prevents burning at the stage base. Final moisture levels can be adjusted by injecting direct open steam.

Flaking The oil within oil-bearing seeds lies in small cells; to make the extraction process efficient, these cells need to be weakened and expanded. This is achieved by flaking the seed so it becomes easier to tear open the cell walls for easier oil extraction. Flake size and thickness are important parameters of oil yield, residual oil in cake and the final solvent extraction meal. Thicker flakes make for more residual oil in the cake, and the preferred cake thickness is about 0.38–0.40 mm. Some oilseeds such as soybean or rapeseed, are conditioned before the flaking process.

Kumar's Flakers are made of carbon steel and cast-iron machinery of heavy-duty construction to flake seeds to an optimum size.

Pre-pressing: A vital step before the solvent extraction process as most of the cells containing the oil are ruptured by the considerable friction and compression forces generated in the prepress.

Kumar's bestselling prepress equipment with a range of 5 to 150 TPD is designed to optimally extract oil from various oil-bearing seeds to a maximum yield at a low operating cost.

Cake cooling: As the cake exits the prepress, water flashes, creating a porous structure ideal for solvent diffusion inside the cake. However, this structure is often ruined while transporting the fragile hot cake to the solvent extractor, leading to the generation of a lot of fines. Consequently, this results in poor percolation leading to poor extraction and high residual oil in cake. The cake must be cooled once it leaves the prepress at about 50-60° C in a cooler with a moisture content of 9 – 10 % before being introduced to the solvent extractor to ensure optimal extraction.

Kumar's Meal coolers are fitted with alloy steel straps, a unique conveying chain, and a perforated sheet for fluidization of meal complete with a driving mechanism.

Expanding: Expanders are used to reform soybean flakes into dense yet highly porous collets for improved extraction efficiency in the extractor. During expansion, injected steam heats the cake under high temperature within a short timeframe. When the expander is discharged, the super-heated water quickly vaporizes, forming collets of pores throughout the material. The added porosity of the material allows for better drainage of the solvent through the material. It improves oil dissolution, which ensures the lowest possible residual oil levels in the meal, less solvent is left behind in the solid product, and less solvent is needed overall for each ton of material processed.

Kumar's Expanders increase plant capacity, reduce hexane consumption and help extract oil of excellent quality.


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For 82 years, Kumar has been delivering dependable process engineering solutions to the oils and fats industry. We're known for our robustly engineered, versatile and operationally profitable plant and machinery. It's why over 500 customers in 65 countries depend on us to solve their processing challenges, big or small. If you’d like to know more about our solutions please fill out the form below:

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