The sunflower oil production process is multi-staged and involves technical and scientific precision resulting from the intersections of agricultural science, mechanical engineering, and food chemistry.
Introduction
Sunflower oil, which is produced from the seeds of Helianthus annuus, is an important, globally significant vegetable oil with a mild taste, good nutritional profile, and versatile uses. It is used for everyday home cooking, large scale industrial food processing, and in food and cosmetic formulations; its uses are massive and growing. Given the current trend towards clean label, high quality and sustainable edible oils, it is helpful to understand the operations related to the full cycle of sunflower seeds, from harvest to refined oil.
The sunflower oil production process is multi-staged and involves technical and scientific precision resulting from the intersections of agricultural science, mechanical engineering, and food chemistry. The sunflower oil production process yields a new consumer product at each production stage starting from raw seed reception and storage to reflexive processes such as demucilagination, neutralization, winterization, and deodorization. Each stage of production has intended isolated applications, yet yields the maximum oil yield; the best sensory characteristics based on viscosity, acid value and the like; and meets health and safety hazards. Advances made in technology development such as solvent recovery, pressing efficiency, and environmental performance improvement continues to impact the production of sunflower oil.
This breakdown serves to unpack the technical dimensions of each production phase for potential value for manufacturers, academic researchers, or any stakeholder that may be interested in better understanding and improving their operating conditions, oil quality, or environmental impacts.
The Stages of the Technological Process for Obtaining Sunflower Oil
1. Reception of Raw Materials
The journey begins with the reception of raw materials, the sunflower seeds themselves. This initial stage is crucial for both quantitative and qualitative assessment. Seeds are carefully checked upon arrival to ensure they meet the necessary standards for processing.
2. Storage of Raw Materials
Once received, the sunflower seeds are moved to storage. This isn't just a simple holding area; it's a controlled environment designed to protect the seeds from degradation. Seeds are typically stored for at least 60 days in specialized warehouses. These facilities are equipped with:
• Unloading lines: For efficient transfer of seeds from wagons and trucks.
• Mechanical installations: For handling, drying, airing, and purifying seeds, preventing spoilage during storage.
Warehouses can vary in construction, including mechanized barns, warehouses with floors, and cell silos (like the metal silos with conical bottoms often seen). Proper storage is vital to prevent deterioration caused by enzymes, microorganisms, or chemical transformations.
3. Cleaning Sunflower Seeds
Even with careful storage, raw materials can undergo degradation, especially if they contain impurities or are wet. This is where cleaning sunflower seeds comes into play. Impurities, which can be mineral (soil, dust, stones) or organic (straw, chaff, weed seeds), can accelerate degradation processes and lead to significant quantitative and qualitative losses.
The cleaning process typically involves two phases:
• Initial cleaning (pre-cleaning): Removes about 50% of the initial impurities before storage.
• Post-cleaning: Further reduces the impurity content to a mere 0.3-0.4%.
Modern seed cleaners utilize various principles for impurity separation, including:
• Sieving: Based on size differences.
• Pneumatic separation: Based on aerodynamic properties.
• Magnetic separation: For ferrous impurities.
4. Drying
Drying the seeds is a critical step aimed at slowing down chemical, hydrolytic, and biochemical processes, and preventing germination and heating. In this process, water is transported from the inside of the seeds to their outer surface, where it's removed by a drying agent. The seed mass temperature must not exceed 70°C. Industrially, heat transfer by convection, conduction, or a combination of both is used. Rotary dryers and drying columns are common equipment for this operation.
5. Peeling
From a morpho-anatomical perspective, oilseeds consist of a shell with a high cellulose content, which is undesirable in the final oil product and processing residues. Therefore, peeling (decortication) is performed to remove this outer layer.
Peeling offers several advantages:
• Increased processing capacity: For installations like rollers and presses.
• Reduced machine wear and tear: Especially for rollers and presses.
• Reduced oil losses in scrap: A cleaner core means less oil is trapped in the discarded shell.
However, peeling also has its drawbacks, such as potential oil losses in the shell and the need for additional installations and energy consumption. For sunflower, a small percentage of shell (around 8%) is intentionally left in the core to optimize pressing and extraction. The process typically involves two phases: detachment of the shell from the core, and then separation of the peels from the mixture. This is often achieved through pounding, using a breaking drum where seeds are impacted and then projected onto a wavy surface for a second impact, aiding in shell separation.
6. Grinding Sunflower Seeds
Grinding is a vital preparatory step for oil extraction. Its primary purpose is to break down the cell membranes and disrupt the oleoplasm structure that contains the oil. From the now "open" cells, oil can be easily extracted by pressing. Oil from "closed" cells, however, requires solvent extraction for recovery.
The success of grinding is influenced by seed humidity and oil content. Optimal humidity leads to a friable, powdery grind, while high humidity results in a sticky mass, hindering pressing and extraction and increasing oil losses. Similarly, very high oil content can lead to excessive oil separation during grinding, resulting in a sticky grind.
For grinding, crushers, rollers, and hammer mills are commonly employed. Hammer mills are particularly useful for grinding scrap due to their robustness, compact size, and high productivity.
7. Hydrothermal Treatment (Roasting)
Hydrothermal treatment, or roasting, is a crucial step to modify the physico-chemical properties of the ground material, aiming for maximum pressing yield, especially for raw materials with over 25% oil content. Roasting before extraction helps achieve plasticity in the ground material, allowing it to be processed into fine, porous, and stable flakes by flattening rollers. These flakes are essential for efficient solvent extraction, as they don't crumble and have an internal structure favorable to solvent penetration.
This treatment occurs in two phases:
• Wetting: Bringing the grind to an optimal humidity.
• Heating and drying: Achieving a specific humidity and temperature for an optimal cellular structure.
Roasting causes a decrease in oil surface tension and viscosity, facilitating its release during pressing. Optimal roasting conditions involve specific steam pressure, roasting time, and controlled initial and final moisture and temperature of the grind. Multi-level cylindrical roasters are typically used for this process.
8. Pressing
Pressing is the technological operation of separating oil from the hydrothermally treated oleaginous meal using presses. This results in crude press oil and "brochettes" (press cakes). Pressing can extract up to 80-85% of the oil, with the remaining oil recovered later through solvent extraction. This method is primarily applied to raw materials with an oil content exceeding 30%.
The pressing duration, typically ranging from 40 to 200 seconds, depends on the physico-chemical characteristics of the grind, and the press's constructive and functional features. During pressing, changes occur in the grind, including a reduction in humidity, transfer of phosphatides into the oil, dissolution of natural pigments, and an increase in oxidized compounds. Both hydraulic and mechanical presses are used, with mechanical presses often favored for their advantages.
9. Solvent Extraction and Solvent Recovery
Solvent extraction is employed to degrease the press cakes (brochettes) or directly process raw materials with lower oil content. The oily material is mixed with a solvent (commonly extraction gasoline), forming a mixture of oil and solvent, while the degreased material is called "scrap."
The extraction process involves several stages:
• Moistening: Solvent moistens the grind particles and carries free oil to the surface.
• Penetration: Solvent penetrates inside the particles.
• Oil Movement: Oil moves from the inside to the outside.
• Boundary Layer Transfer: Oil moves from the particle surface into the diffusion boundary layer.
• Convective Transport: Oil is transported by convection into the stirring current.
Modern factories utilize continuous extraction methods like immersion, repeated spraying, or mixed methods, often using belt extractors, rotary extractors, or basket extractors.
Solvent recovery is crucial because significant amounts of solvent remain in both the oil-solvent mixture and the spent scrap. This recovery typically involves distillation, utilizing the different volatilities of the components. For the oil-solvent mixture, recovery occurs in two phases: pre-distillation and final distillation, where the mixture is heated to evaporate the solvent, which is then recovered. For scrap, solvent is removed by heating, and any remaining heavy fractions are removed by introducing superheated steam. Screw dryers or toasters are used for solvent recovery from scrap.
10. Refining
Refining is the process of removing foreign substances (accompanying substances) from crude vegetable oils obtained by pressing or extraction. These substances, including mucilages, free fatty acids, dyes, waxes, and odorous compounds, can negatively impact the oil's taste, smell, color, stability, and processing. Refining improves the oil's quality and ensures it meets consumer standards. Various physical, chemical, and physico-chemical methods are used depending on the oil's intended use and desired quality.
The main operations in refining edible oils include:
10.1 Demucilagination
Demucilagination removes mucilage, complex compounds primarily composed of phosphatides, albuminoids, and carbohydrates. This step yields high-quality oil, reduces losses during subsequent refining, eliminates an instability factor, and produces valuable lecithin, an emulsifier used in the food industry. Mucilage removal can be achieved by hydration (for edible oils, often activated with citric or phosphoric acid) or acid treatment (for technical oils). Centrifugal separators are used for mucilage separation.
10.2 Neutralization of Oils
Neutralization is absolutely mandatory for edible oils to eliminate free acidity, which is the primary cause of undesirable taste and smell. This is typically done by alkaline neutralization using alkaline solutions like NaOH, which reacts with free fatty acids to form soap. Other methods include neutralization by distillation or esterification. Specialized mixers are used to create the lye-oil mixture in continuous refining installations.
10.3 Oil Washing
After neutralization, the oil undergoes washing with softened water. Using soft water is crucial to prevent the formation of calcium soap (from hard water), which is soluble in oil but insoluble in water and can increase soap content in the refined oil. Maintaining a specific oil temperature (85-90°C) during this phase is important.
10.4 Oil Drying
Following washing, the oil still contains a small percentage of water and traces of soap, which can cause cloudiness. Oil drying eliminates these shortcomings, typically in vertical cylindrical dryers under vacuum. The oil is sprayed into the dryer, and the vacuum helps remove the water. The aim is to reduce the water content to a maximum of 0.05%.
10.5 Discoloration of Oils
Discoloration aims to achieve a clear, shiny, and lightly colored oil suitable for consumption. The natural yellow-orange color of sunflower oil comes from pigments like carotene and xanthophyll. Discoloration is usually achieved by treatment with adsorbents, such as decolorizing earth activated with mineral acids, sometimes supplemented with decolorizing charcoal. The optimal temperature for edible oil decolorization is around 80-100°C, with varying contact times depending on the operation type.
10.6 Winterization (Defrosting)
Winterization (dewaxing) is the operation that removes waxes and saturated glycerides that can solidify at lower temperatures (below 15-20°C), causing turbidity and affecting oil quality. In sunflower oil, the wax content depends on the efficiency of the initial peeling. Winterization involves crystallizing these waxes and solid glycerides, followed by their separation through filtration. Crystallization can be performed in a short or long duration, often incorporating crystallization germs to reduce time. The oil is cooled to specific temperatures, mixed, and then reheated to an optimal filtration temperature.
10.7 Deodorizing
Deodorizing is the final phase of refining, designed to remove substances that produce unpleasant smells and tastes. These substances can originate from the raw material or from chemical transformations during storage and processing (e.g., burning smell from improper hydrothermal treatment, soapy taste from inadequate washing, earthy taste from excessive bleaching). Deodorization combines the effects of high temperature, low pressure, and water vapor. The oil is heated to a high working temperature (200-230°C), and steam is bubbled through the oil or the oil is finely dispersed in direct contact with steam, ensuring effective removal of volatile compounds.
The journey of sunflower seeds from raw material to refined oil is a complex and highly engineered process, ensuring a high-quality product ready for consumption. Each stage plays a vital role in transforming the humble seed into the valuable golden oil we use every day.
