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LECTURE 3�THEME: Grinding oilseeds and kernels. Preparing the roast (meal).

CREATED BY: BEKHZOD KURAMBOEV, ASSISTANT TEACHER, 2 YEAR PhD STUDENT OF THE FOOD TECHNOLOGY DEPARTMENT

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Lecture Objectives:
Understand the purpose and principles of crushing oilseeds and kernels.
Learn the different types of equipment used for crushing and their operational principles.
Grasp the science, purpose, and technology behind the roasting process.
Analyze the key parameters, formulas, and quality indicators for producing high-quality roasted meal.

Part 1: Crushing of Oilseeds and Kernels
1.1 Purpose of Crushing
The primary goal of crushing is to reduce the particle size of the oilseed or kernel to prepare it for subsequent processing, primarily flaking and cooking. The specific objectives are:
Size Reduction: To create smaller, more uniform pieces for efficient flaking.
Hull Liberation: For seeds with hulls (like sunflower, cottonseed), crushing helps to separate the brittle hull from the more pliable meat (kernel).
Increased Surface Area: Prepares the material for more effective heat and moisture transfer during subsequent cooking/roasting.

1.2 Equipment for Crushing
The choice of equipment depends on the type of seed and the desired final product.
A) Bar Crackers / Hammer Mills (for Husked Seeds)
Application: Primarily for seeds like sunflower, cottonseed, and palm kernels where the hull must be separated from the kernel.
Technical Scheme & Principle:

[Whole Seeds with Hulls] --> [Feed Hopper] --> [Rotating Rotor with Swing Hammers/Bars]
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[Impact with Hammers & Liner] --> [Crushed Material & Hulls] --> [Screen/Grate]
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[Hulls & Kernels separated by Aspiration & Screening]
Key Parameters:

Rotor Speed: 1,500 - 3,000 rpm.
Screen Size: 3-8 mm, depending on seed.
Objective: Achieve a clean break, liberating >90% of the kernels from the hulls without generating excessive fines.

B) Corrugated Roller Mills (for Kernels & Dehulled Seeds)
Application: Ideal for soybeans, rapeseed, dehulled sunflower kernels, and peanuts. They offer a more controlled size reduction than hammer mills.
Technical Scheme & Principle:

Principle: Compression and shear forces between two counter-rotating rolls with corrugations.
Scheme:

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[Whole Kernels/Seeds] --> [Feed Hopper] --> [Feeding Roller for even distribution]
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[Nip Point/Gap between Two Corrugated Rolls]
(One fixed, one adjustable spring pressure)
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[Crushed Product (Grits)]
Key Parameters & Formula:

Roll Speed Differential: The two rolls rotate at different speeds (e.g., a 1.5:1 ratio) to create a shearing action.
Corrugation: Number of corrugations per cm (e.g., 4-6 for coarse cracking, 8-10 for fine).
Gap Setting: The most critical parameter. It determines the particle size of the output (grits).

1.3 Statistics for Crushing
Throughput: A typical industrial hammer mill or roller mill can process 100 - 500 tons per day, depending on size and power.
Power Consumption: Hammer mills are generally more energy-intensive.

Efficiency: A well-tuned dehulling/crushing system can achieve a hull removal efficiency of 92-97%.

Part 2: Preparation of Roasted (Meal) Mass
The product from the crusher (grits) is now ready for thermal treatment, commonly known as cooking or roasting. In modern oil extraction, this is a multi-step process of conditioning, followed by roasting in a cooker.

2.1 The Purpose of Roasting/Cooking
This is a critical step that dramatically impacts both oil yield and meal quality.
Coagulation of Proteins: Heat denatures proteins, destroying the cell wall structure that encapsulates the oil. This makes the oil more fluid and easier to extract.
Moisture Adjustment: Optimal moisture is crucial for flaking and extraction. Cooking dries the meal to the perfect moisture level for pressing or solvent extraction.
Enzyme Inactivation: Destroys harmful enzymes like lipase (which causes free fatty acid increase) and urease (in soybeans, important for animal feed).
Sterilization: Kills molds, bacteria, and other microorganisms.
Texture Modification: Makes the material more plastic and suitable for forming flakes in the next step.

2.2 The Science: Moisture and Temperature
The roasting process is a delicate balance of Time (t), Temperature (T), and Moisture Content (MC).
Typical Temperature Range: 90°C - 110°C for cooking; up to 130°C for toasting post-solvent extraction.
Moisture Content (In/Out):

Initial Moisture (after conditioning): ~10-12%
Final Moisture (after cooking/roasting): 3-5% for direct screw pressing; 5-7% for flaking prior to solvent extraction.

2.3 Key Formulas and Calculations
A) Moisture Content ( Wet Basis %)�This is the standard measurement in the industry.�MC_wb (%) = (Mass of Water / Total Mass of Sample) * 100
B) Dry Matter (DM)�DM (%) = 100 - MC_wb
C) Evaporation Rate in the Cooker�To calculate the amount of water that needs to be evaporated.�Water Removed (kg/h) = Feed Rate (kg/h) * [(MC_in - MC_out) / (100 - MC_out)]

2.4 Equipment: The Stack Cooker
The most common industrial equipment is the vertical stack cooker, often a 5- or 6-high stack.
Technical Scheme & Process Flow:
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[Cracked Grits from Crusher] --> [Conditioning Bin: Adjusted to ~10-12% MC, 60-70°C]
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[Top Tray of Stack Cooker]
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[Steam-Heated Trays with Sweeping Agitators] --> [Progressive Heating & Drying]
(Tray 1: ~75°C) -> (Tray 2: ~85°C) -> (Tray 3: ~95°C) -> (Tray 4: ~105°C)
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[Bottom Tray: Discharge at 3-7% MC, 105-110°C]
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[To Flaking Mills or Presses]

The material enters the top tray.
As it moves horizontally across each steam-heated tray, it is agitated by sweep arms.
The temperature increases progressively from top to bottom.
Live steam can be sparged directly into the meal on certain trays to provide both heat and moisture control.
The total residence time in the cooker is typically 30-60 minutes.

2.5 Quality Control of Roasted Meal
The quality of the roasted mass is determined by several lab tests:
Urease Activity Index (for Soybeans): Measures the degree of protein denaturation.

Target: A pH rise of 0.05 to 0.20 units. (<0.05 is undercooked, >0.20 is overcooked).

Moisture Content: As calculated above (3-7%).
Color: A visual and instrumental check. Over-roasting leads to dark-colored meal and oil.

2.6 Impact of Roasting: Statistics
Oil Yield: Proper roasting can increase oil yield during pressing by 1-3%.
Energy Consumption: The cooking/roasting process is energy-intensive, accounting for ~15-25% of the thermal energy in an oil mill.
Throughput: A single large stack cooker can handle 200 - 1,000 tons of material per day.
Summary and Conclusion
The preparatory steps of Crushing and Roasting are not merely mechanical and thermal operations; they are the foundation of efficient and profitable oil extraction.
Crushing creates the optimal particle size, liberates valuable components, and prepares the seed for uniform heat penetration.
Roasting is a scientifically controlled process where time, temperature, and moisture are meticulously managed to:

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