Table of Contents
The parboiling rice process plays a crucial role in rice production by offering significant economic benefits such as improved rice yield and reduced grain breakage during the milling operation.
There are four kinds of parboiling methods, each contributing distinct rice characteristics and textures. The key difference between these techniques lies in the time-temperature combinations used during the soaking and steaming stages.
With that in mind, now let’s take a closer look at each stage in detail.
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Types of Parboiling Rice Process
Sella Process
First comes sella process, Let’s breakdown each step below:
● Kachi Tank Pre-Steaming:
Once the paddy is de-stoned and cleaned, the system feeds it from the storage bin into the Kachi tank for pre-steaming. There, the grains steam sufficiently, ensuring they gelatinize upon subsequent heating at 3-bar pressure.
This pre-steaming operation reduces the soaking time of the paddy and increases the capacity of the rice to absorb water during cooking.
● Soaking:
The steamed paddy then absorbs water for moisture saturation and generalization.
● Pakki Steaming System:
The process drains the soaked paddy before transferring it for final steaming at 3-bar pressure.
● Tapered V Dryer:
The specialized drying mechanism reduces the paddy’s moisture content from approximately 36% to 12% through evaporation.
● Transported to Rice Mill:
The system cools down the processed paddy to room temperature before transporting it to the rice milling area for final rice production.
Full-Boiled Rice Process
Boiled or parboiled rice involves full gelatinisation of grain. Here are the detailed steps:
● Soaking:
In this process, the cleaned paddy is first soaked and circulated in hot water at 70 degrees Celsius.
● Online Cooker:
The soaked paddy is lifted by an automated conveyor system and enters an online cooker, where high-pressure steaming at 3 bars enhances gelatinization.
● Tapered V Dryer:
The specialized drying mechanism reduces the paddy’s moisture content from approximately 36% to 12% through evaporation.
● Transported to Rice mill:
The system cools the processed paddy to room temperature before transporting it to the rice milling area for final rice production.
Half-Parboiled Rice Process
This process concentrates on Half-gelatinisation of rice which takes less steaming period than bolied rice.
● Soaking:
In the half-boiled rice process, the cleaned paddy is soaked and circulated in cold water at ambient temperatures to increase the moisture content and enhance the gelatinization of kernel.
● Online Cooker:
The paddy is mechanically elevated by an automated conveyor system and fed into an online cooker, where the soaked paddy undergoes continuous steaming at 0.8 – 2 bar pressure.
● Tapered V Dryer:
The paddy is dried using a specialized drying mechanism to evaporate moisture content from approximately 36% to 12%.
● Transported to Rice mill:
The processed paddy is then cooled down to room temperature and transported to the rice milling area for final rice production.
Steamed Rice Process
This method accelerates the aging of rice using the curing process:
● First-pass Drying:
In this process, the paddy is directly fed into the dryer system, where the moisture content is brought down to 18%-20%.
● Online Cooker:
The dried paddy is fed into an online cooker for final steaming at 0.8 – 1.5 bar pressure.
● Second-pass Drying:
The steamed paddy is again dried to reduce the moisture content from 32% to 12%.
● Transported to Rice mill::
The system cools the processed paddy to room temperature and then transports it to the rice milling area for final rice production.
Conclusion
Each of these parboiling techniques follows a unique combination of soaking, steaming, and drying. Carefully monitoring temperature and pressure at each stage will ensure better texture, nutritional retention, and market value. For more information on paddy parboiling plant machinery click here.
FAQ
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What is the Main Purpose of the Parboiling Process?
The primary purpose of paddy parboiling is to improve milling efficiency, reduce grain breakage, and increase total rice yield, while also enhancing nutritional value and storage stability. Parboiling involves soaking, steaming, and drying paddy (unhusked rice) before milling, which alters the grain’s physical and chemical properties.
Detailed Benefits:
Reduced Grain Breakage: The steaming process gelatinizes the starch in the grain, making it harder and more resilient. This reduces breakage during milling from 20–40% (for raw rice) to 2–5% (for parboiled rice), significantly increasing the yield of whole grains, known as head rice yield (up to 70% in modern plants).
Increased Total Rice Yield: By minimizing broken grains, parboiling ensures more marketable rice, boosting economic returns for millers. For example, a 10-ton paddy batch could yield 6.5–7 tons of head rice post-parboiling, compared to 5–6 tons for raw rice.
Nutritional Enhancement: During steaming, nutrients like B-vitamins (thiamine, niacin) and minerals from the bran migrate to the endosperm, making parboiled rice more nutritious than polished white rice. This is critical in regions with dietary deficiencies.
Improved Storage Life: The gelatinized starch and reduced moisture content (12–14% post-drying) make parboiled rice less susceptible to insect damage and fungal growth, extending shelf life by months compared to raw rice.
Enhanced Cooking Quality: Parboiled rice grains are firmer and less sticky, ideal for dishes like biryani, pilaf, or industrial products (e.g., instant rice, canned foods).
Read more on why parboiled rice processing is superior than milled rice products.
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Can All Types of Rice Be Processed in a Paddy Parboiling Plant?
Yes, most rice varieties—basmati, non-basmati, long-grain, short-grain, indica, or japonica—can be processed in a paddy parboiling plant. However, operators often adjust machinery settings or specialize equipment to accommodate the unique characteristics of different rice varieties, ensuring optimal quality and yield.
Key Considerations:
Varietal Differences:
Basmati: Known for its aroma and long grains, basmati requires precise soaking (shorter duration, ~4–6 hours) and lower steaming temperatures to preserve its delicate flavor and texture. Over-parboiling can dull its aroma.
Non-Basmati (e.g., IR64, Sona Masuri): These sturdier varieties tolerate longer soaking (8–12 hours) and higher-pressure steaming, making them ideal for standard parboiling plants.
Short-Grain Varieties: Common in sticky rice dishes, these require careful drying to prevent clumping post-parboiling.
Machinery Adjustments:
Modern plants (e.g., Photons Food Machinery) offer customizable settings for soaking time, steaming pressure (6–8 bar), and drying rates to suit specific varieties.
Specialized plants, like those for golden sela basmati in North India, use pressure parboiling to achieve the desired yellowish hue and firm texture.
Challenges: Some aromatic varieties (e.g., traditional basmati) may lose sensory qualities if not processed carefully. Operators must calibrate equipment based on grain size, starch content, and market preferences.
Universal Compatibility: Most Indian manufacturers, such as Dulichand Technico or Shree Sai International, design plants with modular components (e.g., adjustable soaking tanks, multi-stage steamers) to handle diverse varieties, from 5 to 100 tons/day.
Best Practice:
Consult with manufacturers to tailor equipment for your target rice variety. For mixed-variety operations, invest in automated systems with recipe-based controls to switch settings seamlessly. Testing small batches ensures quality before scaling up.
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What Happens to the By-Products of Rice Processing?
Rice processing, including parboiling, generates several by-products—husks, bran, and broken rice—that can be repurposed for economic and environmental benefits. These by-products are not waste but valuable resources for energy, food, and industrial applications.
By-Products and Their Uses:
Husks (20–25% of paddy weight):
Energy Production: Husks are burned in biomass boilers to generate steam for parboiling or electricity for the plant, reducing energy costs. For example, Mill Mech Engineers’ plants use husk-fired boilers for sustainable operations.
Other Uses: Husks are used as fuel in rural households, as bedding in poultry farms, or as a raw material for biochar and silica production (e.g., in cement or ceramics).
Bran (5–10% of paddy weight):
Rice Bran Oil: The bran layer, rich in oil (15–22%), is processed into edible rice bran oil, widely used in cooking and cosmetics. India produces over 1 million tons of rice bran oil annually.
Animal Feed: Defatted bran is mixed into livestock and poultry feed due to its protein and fiber content.
Nutritional Products: Bran is used in health supplements for its antioxidants (e.g., oryzanol).
Broken Rice (2–5% in parboiled rice):
Animal Feed: Broken grains are incorporated into cattle and poultry feed.
Brewing and Food: Used in beer production, baby foods, or processed into rice flour for snacks and noodles.
Industrial Uses: Broken rice serves as a starch source in adhesives or fermentation processes.
Management Tips:
Recycling: Invest in husk-fired boilers or biogas systems to power parboiling plants, as seen in Essar Enviro Air Systems’ designs.
Value Addition: Partner with oil extraction units to monetize bran; sell broken rice to food processors or breweries.
Sustainability: Proper handling (e.g., drying husks to <10% moisture) prevents spoilage and maximizes by-product value.
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Is There an Environmental Impact from Paddy Processing Plant Operations?
Yes, paddy parboiling plants can have environmental impacts, primarily from energy consumption, water use, and waste. However, modern technologies and proper waste management significantly reduce these impacts, aligning with sustainability goals.
Environmental Impacts:
Energy Use: Traditional parboiling relies on wood or husk-fired boilers, contributing to deforestation or emissions (CO2, particulate matter). Steaming and drying consume significant energy (e.g., 100–150 kWh/ton).
Water Consumption and Wastewater: Soaking requires large volumes of water (1–2 liters/kg of paddy). Improper disposal of nutrient-rich wastewater can pollute local water bodies, causing eutrophication.
Air Pollution: Burning husks in inefficient boilers releases smoke and ash, impacting air quality in rural areas.
Solid Waste: Mismanaged husks or bran can attract pests or decompose, creating odors and health hazards.
Mitigation Strategies:
Energy-Efficient Machinery: Modern plants from SDF Dryers or Photons Food Machinery use fluidized bed dryers and low-energy steamers, cutting power use by 20–30%. Biomass boilers (using husks) reduce reliance on fossil fuels.
Water Management: Recycling soaking water or treating it with filtration systems prevents pollution. Some plants use closed-loop systems to reuse 50–70% of water.
Emission Control: Install scrubbers or filters in boilers to capture ash and reduce emissions. Solar dryers, as offered by some Indian manufacturers, eliminate burning entirely.
Waste Utilization: Convert husks into energy or biochar, and sell bran for oil extraction. This creates a circular economy, minimizing landfill waste.
Regulatory Compliance: Adhere to India’s environmental standards (e.g., CPCB norms) for wastewater and emissions to avoid penalties.
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