Rice is one of the most widely consumed cereal crops globally. It is so popular because it is a great source of carbohydrates, minerals like calcium and iron, and vitamins like vitamin E, thiamine, folate and pantothenic acid. Across many countries, especially in Asia and Africa, rice is a part of people's culture, their culinary identity.
When rice is milled, 70% of the resulting product is the endosperm or the rice grains that we cook and consume. The remaining 30% comprises 20% husk, 2% germ and 8% bran.
What happens with this remaining third? Well, a lot of the time, it gets thrown away. But for us at Kumar, the idea of not making the most of the natural resources available to us is unthinkable.
Using waste as a resource: Rice bran as an important but overlooked source of nutrition
Rice bran is the focus of our interest in this series of blog articles. Or more specifically, it is the rice bran oil production process. After all, for a company committed to using waste as a resource, how could we ignore the transformative economic and nutritional potential of the rice bran oil making process?
Rice bran is becoming increasingly popular for its biologically functional components. Not only does rice bran have antioxidant properties but it is also being recognised for its anti-inflammatory activity and associations with reduced cancer incidence, coronary heart disease and decreased cholesterol levels. The phytic acid present in it is also said to prevent cancer, diabetes, renal calculi, hypolipidemic effect and Parkinson's disease.
Given the widespread cultivation and consumption of rice, large quantities of rice bran remain as by-products of rice milling. It is only reasonable that these massive amounts of bran should be put to good use, especially considering their nutritionally rich profile. As vehement advocates of value addition and circular economies, we at Kumar are committed to extracting the maximum value from rice bran as a valuable agricultural by-product.
This series of articles serves as a practical guide for edible oil manufacturers who want to make the most of this rice milling by-product. From bran preparation to extraction, refining and downstream value addition, we'll explore the rice bran oil making process and everything that accompanies it. So that when you decide to take the leap, you know exactly where to get started in setting up your rice bran oil solvent extraction plant.
What is rice bran oil?
Unlike many other plant-based edible oils which are extracted from the seed or fruit, rice bran oil - as its name suggests - is unique in that it is derived from the bran of the rice cereal. Bran comes from the brown outer layer or husk of the rice kernel. Obtained as a by-product of the milling process, rice bran generally has an oil content of 18 to 22%. This oil is rich in monounsaturated, polyunsaturated and saturated fatty acids. However, based on the variety of rice and how it is milled and treated, its oil content and chemical composition may vary.
The market for rice bran oil
To a large extent, the applications of rice bran oil have been niche - in cosmetics, nutraceuticals and pharmaceuticals. But increasingly, the rice bran oil making process is being employed by edible oil manufacturers.
Beyond its attractive nutritional profile, rice bran oil is gaining popularity as a cooking oil because it has a high smoke point and a mild flavour. More and more health-conscious consumers in countries like India, China, Japan, Korea and Indonesia are picking up rice bran oil from supermarket shelves.
The market for rice bran oil isn't as large as the markets for, say, palm oil or sunflower oil. But slowly, steadily and undoubtedly, it is growing. If you're looking to invest in a rice bran oil solvent extraction plant, there is no time like the present!
So how do you get started with the rice bran oil production process? Let's dive right in.
The rice bran oil making process: The need for an experienced process partner
The rice bran oil making process is complex. You need a comprehensive understanding of not only edible oil production technologies but also the physical, chemical and biological properties of rice bran itself.
Since rice bran oil is not obtained from the protected seed of a fruit, in its crude form, it is full of impurities which must be eliminated. Rice bran also contains an enzyme called lipase which converts the neutral oil to free fatty acids (FFAs) and partial glycerides. To prevent the formation of these undesirable compounds, you must either stabilize the bran right after milling or take it straight to your rice bran oil solvent extraction plant with no delays.
Despite all the precautions you take, your rice bran oil can have a fairly high FFA content. Refining crude oil using chemical methods like alkali neutralisation results in high oil losses and the elimination of extremely healthy and desirable micronutrients. You need physical refining, enzymatic reactions and other such processes to retain nutritional elements while neutralizing the FFAs and minimising oil loss.
Even later in the life cycle of rice bran oil, oxidation during processing, storage and cooking can lead to the production of ketones, aldehydes and other components that take away from the benefits of the oil.
Given all these challenges, it's safe to say that you need a competent and experienced process partner to ensure that you get your rice bran oil production process right every single time. It's also important that you yourself have a good understanding of the process so that you can ask the right questions and make an informed decision while choosing a process partner to work with.
That's exactly what we'll do in the next part of this blog post - give you a comprehensive look at the entire rice bran oil production process so that you're empowered to make the decisions that are best for you.
As promised, this section is all about empowering you with the knowledge you need to make informed decisions as you embark on the rice bran oil production journey.
The rice bran oil solvent extraction process
Mechanical extraction vs solvent extraction
Rice bran oil can be extracted using mechanical extraction, also referred to as cold pressing. This process involves the use of a screw press with the application of little to no heat. No organic solvent is used either.
Mechanically extracted oil requires less labour and a lower financial investment. It is safer, retains a high level of nutrients, and produces 100% chemically-free end products. Nonetheless, this process has one major drawback: it is extremely inefficient, with 8 to 14% of the oil being left behind in the cake. Given that rice bran already has a comparatively low oil content, not being able to capture this 8 to 14% is a problem.
As with other oleaginous materials with low oil content, rice bran is best subjected to solvent extraction to obtain a high oil yield. Given our 80+ years of experience in the edible oils industry, we at Kumar also recommend using solvent extraction with hexane for your rice bran oil production process.
Ongoing research has resulted in the emergence of non-conventional extraction techniques for rice bran oil. While these techniques circumvent some of the issues associated with conventional solvent extraction, they are either fairly new, not yet the industry standard, or unsuitable for production at scale. Nonetheless, we will discuss them in later sections of this post.
Rice bran preparation
Before you can get into the rice bran oil solvent extraction process, you need to understand the preparatory steps that make the bran suitable for extraction. The process is fairly straightforward. Conditioning is followed by pelletizing and then cooling.
Conditioning
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Pelletizing
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Cooling
Conditioning involves heating the oil-bearing material - in this case, the bran - to the desired temperature. The applied heat ruptures the oil cell and eliminates any internal moisture as steam. This makes it easier to separate the oil from the meal.
This step is indispensable in the rice bran oil production process. Let's take our Stack Cooker/Conditioner, for instance. In this vapour-tight carbon steel equipment, the bran achieves the desired moisture content, leading to fewer milling defects and lower power consumption in subsequent steps.
Next comes palletization or pelletizing.
After milling, rice bran is obtained in a powdery form which makes oil extraction difficult. So, you must convert it into pellet form to enable uniform solvent percolation and minimal wastage. This step is crucial because it facilitates a more efficient and regulated rice bran oil solvent extraction process.
Different pelletizers - of horizontal, vertical and extruder types - are available on the market. Take Anderson's Dox™ Extruder, which is particularly effective in treating oil-bearing material with low oil content, usually of less than 25%. When used for extrusion pre-treatment, you can minimise the amount of oil left in the meal to about 5%.
The final preparatory step before extraction is cooling. In this step, the rice bran pellets are cooled to attain a temperature that is optimal for extraction. Kumar's Flake Drier/Cooler is a good choice of equipment for this process.
Rice bran oil extraction
Preparatory steps are followed by the rice bran oil solvent extraction process. Solvent extraction is not unique to rice bran oil - it is used (sometimes in combination with mechanical extraction) to obtain sunflower oil, soyabean oil, castor oil, palm kernel oil, and many others.
This process, extremely common amongst edible oil manufacturers, involves the use of an organic solvent, typically hexane. The solvent is sprayed over the prepared oil-bearing material, be it an oilseed, bran or kernel. The solvent dissolves the oil present in the feedstock. The oil-solvent mixture or miscella is separated from the cake-solvent mixture. Finally, the solvent is recovered from both the miscella and the cake; manufacturers that value sustainability reuse the recovered solvent for the next cycle of production. The extracted crude oil goes to a refinery so that the impurities in it can be removed. The cake or meal is used as feedstock in the production of animal feed, biomass and other downstream value-added products.
In the rice bran oil production process, we recommend carrying out solvent extraction using the Anderson Solvex™ Expander. This cutting-edge machine packs the raw material into a dense yet porous structure, allowing the solvent i.e. hexane easier access to the oil. The unique features of this machine result in a 50% higher extractor capacity, 40% lower solvent hold-up in the solid product, 20% less solvent in the miscella and an overall reduction in solvent losses.
In short, the Solvex™ Expander is extremely energy- and resource-efficient, helping you get the best value from your inputs. By reducing overall energy consumption in your rice bran oil solvent extraction plant, you will reduce your operational costs while processing more material in a given timeframe.
Refining crude rice bran oil
After solvent extraction, you have your crude rice bran oil. But to make it suitable for consumption, you must treat it in an edible oil refinery.
The rice bran oil refining process includes the steps of degumming, pretreatment and bleaching, dewaxing, post bleaching, deodorization and deacidification, and winterization. In each of these steps, a different piece of equipment is used and different by-products are generated.
Degumming, as the word suggests, is the process used to remove gums from the oil. Depending on the type of oil and phosphatides present in it, you may have to use water, acid or enzymatic degumming. Enzymatic degumming is used for rice bran oil. In this process, the oil is hydrated and treated with enzymes which react with phosphatides, separating the phosphorous group from the lipid group into distinct oil and water-soluble compounds. Use a centrifugal separator and voila! You have degummed oil. Wet gums are a by-product of this process.
The next step? Pretreatment and bleaching. In this step, unwanted colours, phosphorous content, residual soap content, peroxide and metal contaminants are removed from the crude rice bran oil. We recommend using either our Ecopure Bleacher or our Stable Bleacher, depending on the scale, space, energy, labour and maintenance services available to you. Spent earth is a by-product of this process.
Then comes dewaxing, the process in which high-melting non-triglyceride components are separated by crystallization followed by filtration. Wax oil is a by-product of this process.
After another round of bleaching, you would carry out deodorization and deacidification. This involves the elimination of free fatty acids (FFAs) and volatile components from oil responsible for odours and colours. This is the most critical stage in the rice bran oil refining process and generates fatty acid distillate as a by-product, used as a raw material in the oleochemicals industry.
We highly recommend using our EcoPack Deodorizer for this step in your rice bran oil refining process. This piece of equipment is specially designed to refine oils with an FFA content above 3%. It has an environment-friendly chilled water vacuum system and in-built vacuum heat recovery heat exchanger. Not only does it use relatively low quantities of steam but it also offers improved oil stability and easy access for maintenance.
Finally, the last step in rice bran oil refining. Winterization. The process by which high melting triglycerides, responsible for the formation of turbid oil during cold weather, are separated from the oil. This step is generally optional; you can decide to use it based on your desired product quality.
And there you have it. Refined rice bran oil, ready to be packaged and transported to distributors, wholesalers, retailers or consumers. Ready for use in the culinary industry as well as in the production of nutraceuticals, pharmaceuticals and cosmetics.
Emerging non-conventional techniques in rice bran oil extraction
So far, we've explored mechanical extraction and solvent extraction in the rice bran oil making process. We've also discussed why solvent extraction is the preferred technique for rice bran.
Despite the widespread use of solvent extraction to make rice bran oil, the technique does have some drawbacks. For instance, hexane produces rice bran oil with poor colour quality and poses serious environmental and human health hazards due to its toxicity. Further, given its toxicity, large amounts of energy and attention have to be paid to solvent recovery technologies.
For this reason, beyond finding alternative solvents, the scientific community has also developed new green extraction techniques to make the rice bran oil making process more sustainable and environmentally friendly.
Supercritical CO2 extraction
Supercritical CO2 extraction is a separation technology which uses a supercritical fluid (in this case, carbon dioxide above its critical temperature and pressure) to separate oil from the oleaginous mass. This method is faster and more efficient than conventional oil extraction techniques because it has a higher penetration power into the raw material. It poses no risk of solvent contamination. Interest in this specific type of supercritical fluid extraction has increased in recent years.
Subcritical CO2 fluid extraction
The above process also has some drawbacks. In response to these challenges, scientists developed the subcritical CO2 fluid extraction technique. While this method is based on the same principle as the previous one, the temperature and pressure conditions for it are different. In subcritical CO2 fluid extraction, you must maintain a temperature below 31.1 °C and CO2 pressure of 72.9 bar.
Subcritical water extraction
This rice bran oil making process uses subcritical water, which is water under the pressure of 22.1 MPa and below the temperature of 374 °C. This subcritical water behaves similarly to organic solvents and helps to extract bioactive compounds with different polarity. While less conventional, this method offers similar results as the process of hexane extraction.
Ultrasound-assisted extraction
The use of ultrasound-assisted extraction is becoming increasingly common in the edible oil extraction industry. This is, in some ways, a form of mechanical extraction. It involves transmitting ultrasound waves through the medium, which causes an excitation in the form of enhanced molecular motion. This increased molecular motion leads to the creation of cavities which enhances the permeability of the oil-bearing tissues.
In essence, the ultrasound waves cause mechanical damage to the oil-bearing material which, scientists have found, results in high extraction yield, low solvent use, short extraction time, low running cost, high reproducibility, limited environmental impact, and easy adaptation to industrial scale use. This method is popular because it produces rice bran oil which has a lower FFA content and fewer colour imparting components.
Microwave-assisted extraction
The last non-conventional rice bran oil extraction technique that we're exploring is microwave-assisted extraction. It is becoming increasingly popular because it boasts benefits like short extraction time and low energy and solvent consumption. Most importantly, this process can be carried out under atmospheric conditions, reducing the risks and safety concerns associated with other methods.
Producing rice bran oil within a sustainable circular economy
Among all the plant-based oils produced for human consumption through food, rice bran oil is unique. Many other oil-bearing crops - sunflowers, soybean, castor seeds, mustard rapeseed etc. - are cultivated with the intention of extracting oil from them. In other words, oil is one of the main products derived from these crops.
Rice bran, on the other hand, is often considered a waste product - a nuisance to get rid of rather than an important resource to utilize. Fortunately, that perception of rice bran is changing. But the fact remains that rice crops are cultivated primarily for the cereal that many of us eat in our meals. The bran is always a "by-product".
Using rice bran to obtain edible oil is one of the best examples of deriving value from waste. Nevertheless, there are several other ways in which your production of rice bran oil can be ethical, sustainable and aligned with the principles of a circular economy.
Sustainable sourcing
To ensure that your production processes are environmentally friendly, it is important to source your rice bran from farmers who cultivate rice in ethical and planet-friendly ways. This means avoiding the use of harmful chemical pesticides and fertilisers. It means assessing their labour and land use practices to ensure that their ESG commitments align with yours.
Short supply chains
One of the biggest benefits of eating local is the short supply chain. This means that relatively less energy is expended in transporting your food from where it is produced to where it is consumed. This principle holds for manufacturers of sustainable rice bran oil as well. You should try to set up your rice bran oil solvent extraction plant either close to where you source your raw material from or close to where your consumers are. This will minimise your carbon footprint in terms of logistics and transport.
Energy-saving technology
Large amounts of energy are expended to recover hexane from the extracted rice bran oil and remaining meal or cake, to condition the rice bran, and to refine the crude oil. Find equipment and process partners who prioritise energy efficiency in their design. Not only will this make your operations more planet-friendly but it will also reduce your operating costs.
Safer solvents
Hexane is the go-to solvent in the edible oil manufacturing industry. But given its toxicity, it would be preferable to use alternative solvents when research in the industry provides them. While you may still use hexane combined with efficient hexane recovery technology, keep an eye out for greener solvents and extraction techniques that allow you to use these.
Downstream value addition
Just as rice bran is a by-product of the rice production process, many additional by-products are obtained when we extract rice bran oil and refine it. For instance, wet gums are produced during degumming - wet gums are used to make lecithin, which has applications as an emulsifier in the food industry. The fatty acid distillate obtained during deodorization and rice bran oil itself serve as feedstock for oleochemicals used in cosmetics, lubricants and other chemical industries. As you can see, producing rice bran oil is far from the end of the value chain.
In this three-part blog post, we've covered all you need to know about rice bran oil - why you should produce it, how to produce it, and how you can ensure the sustainability of your operations. While we've covered all the basics, to come up with a detailed plan that is right for you, your budget and your specifications, we recommend that you get in touch with our expert team.
We, at Kumar, have been in the edible oil plant business for over 80 years. We've successfully delivered over 700 projects for nearly 600 customers across more than 74 countries. We're very experienced, to say the least.
If you're looking to enter the rice bran oil production business, there's no better time to start than today. If you need a process partner to get you set up, there's no better partner than us. Get in touch with us today.
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