What it is:
Oils are refined to increase their stability, shelf-life, smoke-point, and to neutralize flavor. Plant oils that have been refined are used across a wide variety of areas in the food industry, from home cooking to food processing. However, having a firmer grasp of the methods and types of cooking will help you select the most suitable oil for your needs.
The type of processing and refining an oil goes through affects how it will be used to manufacture and cook foods. But recognize that the choices are not just about what you're eating but what the food industry determines to be the cheapest and easiest to transport, sell, and store.
Purported claims:
Crossing the smoke point produces harmful compounds
Plant oils can be heavily processed and washed with toxic chemicals.
What the science says:
Extraction and Refinement
Oil extraction involves the physical or mechanical removal of oil from oil-bearing materials. The less heat utilized during the extraction method preserves the oil’s natural flavor, aroma, and nutritional qualities.
Mechanical
Cold-pressing = the traditional mechanical squeezing of a plant to extract the highest quality, nutrient-dense, and flavourful oil. It minimizes heat exposure.
However, it will have a shorter shelf life, low yield, and higher price.
Expeller (Mechanical-pressing) = the temperatures generated during the mechanical pressing can vary due to friction, resulting in elevated temperatures and possible loss of quality.
Hot pressing = the oil-bearing material is heated before being fed into the press using steam or direct heat.
Chemical
Solvent extraction = the oil-bearing material is bathed in the solvent hexane, which extracts the oil due to its volatility.
This is the most cost-effective, efficient, high-yield method for manufacturing production.
However, there are significant concerns with this method:
Residual Solvent: One of the primary issues is the potential presence of residual solvents in the extracted oil. Despite efforts to recover and recycle the solvent, small amounts may remain in the final oil product. While the levels are typically within regulatory limits, safety concerns exist.
Hexane is classified as a hazardous pollutant and may cause adverse health effects such as neurotoxicity and respiratory irritation.
Foods prepared using solvent extraction are most likely fine in small, occasional quantities. However, reducing the amount of low-quality oils in your eating habits may have a considerable long-term impact on your health.
Once an oil has been extracted it is then refined or purified to remove undesirable components and enhance stability. The series of physical and chemical processes remove colour, free fatty acids, flavours and solids. This is to improve consistency of the item.
For example, winterization removes waxes and other high-melting-point compounds, particularly in oils that may solidify or become cloudy at low temperatures. This process is intended for oils that will be used in cold climates or applications where clarity and stability are necessary, such as salad dressings, mayonnaise, and other food products.
However, for everyday application in foods, removing these compounds also strips away the benefits. So, if you're consuming olive oil for its health-promoting properties like antioxidants, you want to source the purest, freshest form possible. A cold-pressed, extra virgin olive oil will be the highest quality item for everyday consumption.
Cooking and Smoke Point
The smoke point occurs when an oil is heated and reaches the threshold at which it begins to smoke. Olive oil's smoke point is between 365°- 420°F, whereas canola oil has a high point at ~400°F. Virgin or cold-pressed oils tend to have a lot of flavor and aroma, but this also means these compounds tend to burn more readily. Refined oils are used when cooking with high heat as they are less likely to break down and produce harmful compounds at high temperatures.
As oil oxidation is a complex process with many chemical reactions, there has been uncertainty surrounding smoke points being a predictor of oxidative stability. The more unstable an item is, the more oxidative stress it can cause in the body. In a recent study (De Alzaa, 2018), extra virgin olive oil produced the lowest level of polar compounds. Previous studies had stated that olive oil's low smoke point meant it would produce more negative compounds; therefore, higher smoke-point oils should be used. Although this is just one study, it shows the complexity of choosing a cooking oil.
Most at-home cooking will not reach heat levels to be overly worried about. So, as long as you avoid highly processed, deep-fried foods, exposure to free radicals and harmful compounds, will likely be limited.
However, when an oil reaches its smoke point, it negatively impacts the meal's flavor and smell, leading to a burnt or bitter taste. Therefore, it is advisable to use proper cooking techniques, such as maintaining moderate heat levels and avoiding prolonged heating.
Although refining an oil is beneficial for some situations, it also reduces the nutritional content, such as antioxidants and vitamins. For many methods commonly used in home cooking, such as sautéing, stir-frying, baking, and light frying, the temperatures typically do not exceed the smoke points of unrefined oils. Therefore, unrefined oils, such as extra virgin olive oil, canola oil, or cold-pressed oils, can often be used effectively without the need for refining.
The benefits of extra virgin olive oil, canola oil, and other plant-based oils may outweigh the minor, if existent, possibility of going above the smoke point when home cooking. Take into account:
Canola oil has been bred to have a high smoke point while retaining the beneficial compounds. Use Canola oil for cooking or frying, as this oil handles direct heat from the pan well.
Olive oil is best for oven roasting or sauteeing as it retains the beneficial compounds as long as there is limited direct high heat.
Our take:
Consume healthy oils such as cold-pressed, extra virgin olive oil in salads, when lightly sauteeing, or when roasting foods at medium temperatures. Cold-pressed canola oil is another option for a milder, more neutral flavor. Change up the variety with unrefined items such as flaxseed, walnut, sesame, and hempseed oils. They are fantastic as finishing oils, drizzled over foods, or mixed into dressings with bountiful health properties.
Sourcing your oils from trusted vendors is vital, as the black market for fake and mixed oils is lucrative. It's worth paying top dollar for healthy oils, but ensure you're getting what you pay for.
Only occasionally, if ever, consume deep-fried or high-heat fried foods. If you choose to consume these foods, make it rarely and don't fret about it too much.
Will this benefit you?
Knowing which oils to use and when to use them can reduce your exposure to inflammatory compounds while enhancing your meals. Consuming high amounts of anti-oxidants may also help offset adverse effects from the breakdown of free radicals, as once the cascade begins, it keeps going. However, antioxidants react with the radicals to slow down the cycle. Therefore, source the purest form of oils and consume them alongside antioxidant-rich foods.
Still curious to try it? If you do, here’s what to keep an eye on:
To prevent rancidity and destabilization of oil:
Avoid heating oils at extreme temperatures (deep frying), and change the oil often if you must cook at this heat.
Keep oils in dark bottles in the back of your cupboard to reduce their exposure to light.
Also, select oils from the back of the grocery shelf.
Buy oils in small quantities or decant bottles into smaller vessels to limit exposure to air, which can lead to deterioration by oxygen.
Storing all oils/seeds/flours/whole grains in the fridge can lessen exposure to light/heat and prevent the fats from going rancid.
References and additional reading:
Mahan, L K, and Raymond, J L. Krause's Food & the Nutrition Care Process. Elsevier Inc, 2017. Print.
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