Written by: Zenani Sizane
If you regularly use plant oils or are an enthusiastic DIYer, you are aware that all plant oils are made from plant extracts, each with a distinct extraction process. Additionally, because they are plant extracts, they can be highly fragile and heat sensitive. It's likely that you are aware that certain oils are heat-sensitive and that, if heated too much, some oils can lose their primary therapeutic properties.
In this article, we are going to answer all the questions you may have about oils that are sensitive to heat and how to protect the integrity of plant oils by heating them in the correct way so that you do not lose the best of their healing or restorative properties, fatty acid profile, and active components.
As stated in the introduction, plant oils are derived from plants, which is why they can be delicate and sensitive. In most manufacturing processes, some formulas frequently use heated phases, and this is where you would need to know the iodine value of the ingredients you are using in your product, because having a heat-sensitive ingredient in the heated phase can render it less beneficial, destroy some of its active properties, and ultimately mess up your entire formulation.
How to determine plant oil heat sensitivity
To determine an oil's heat sensitivity, you must first become acquainted with the oil and learn more about it so that you can heat it correctly without losing any of its main components or properties, allowing you to reap all of the oil's benefits.
Carrier oils are all classified as lipids, which are made up of chain-like molecules of hydrogen, carbon, and oxygen known as glycerols and fatty acids (which can be saturated or unsaturated); phospholipids, tocopherols, fat-soluble minerals and vitamins, and phytosterols can all contribute to the oils' unique properties. It is also considered that the method used to extract the oil from the plant, whether cold-pressed or refined, can make a big difference in defining an oil's heat sensitivity. (Van Der Meer)
When determining heat sensitivity in oils, keep in mind that the higher the unsaturated fat content, the more heat sensitive the oil. Unsaturated fats are oils that are liquid at room temperature, are primarily vegetable-derived, and contain at least one double bond in their fatty acid chemical chains. (Van der Meer) Unsaturated fats are thought to be better fats in the diet.
Saturated fats, on the other hand, tend to become solid at room temperature and require heat or hot weather to become liquid, making them more heat stable than unsaturated fats. Because the fatty acid chain of saturated fats only has single bonds, you must search the oil's composition to determine its heat sensitivity.
Another way to determine an oil's heat sensitivity is to look up its iodine value. As previously stated, the higher the unsaturated fat of the oil, the more heat sensitive it is, and the iodine value is a measure of an oil's degree of unsaturation, which then determines the oil's heat sensitivity. The higher an oil's iodine value, the more sensitive it is and requires more protection from heat, light, and oxygen.
Any oils with an iodine value of more than 100 should not be heated, especially for an extended period of time. If that is the case, you will need to heat the oil carefully. It is always recommended to heat the oil briefly and add antioxidants such as Vitamin E to help protect it.
Furthermore, in addition to the oil's unsaturation, it is important to consider any special features the oil may have when determining its heat sensitivity, as well as the vitamins and omega fatty acids it may have, as these are the components that can be thermally unstable.
The iodine value is an excellent predictor of the stability and shelf life of the lipids we work with. It is also vital to note that there is no rule of thumb or linear link between the oil's iodine content and its shelf life. This is not a science, but rather a user's guide.
Does the shelf life of an oil contribute to the plant’s heat sensitivity?
Aside from the iodine value and the composition of the lipid, several additional factors influence the shelf life. rancidity occurs in three ways: microbiological rancidity, hydrothermal rancidity, and oxidative rancidity.
Plant oils are degraded into components that alter the aroma, look, and texture/feel of the oil in any of several degradation routes. (Eghbali)
Both hydrothermal and oxidative rancidity are faster in oils with a larger degree of unsaturation, which includes monounsaturated and polyunsaturated fats. Simply put, the higher the unsaturation, the more vulnerable the oil is to heat and oxidation, resulting in a shorter shelf life.
When determining heat sensitivity of lipids, we must consider a variety of aspects, including the presence of unsaponifiable (particularly tocopherols and carotenoids), temperature and extraction procedures, oil origin, and so on. That is why it is recommended that you avoid heating oils with iodine values greater than 100.
The iodine value of a lipid is often given in its technical data sheet; nonetheless, we have included a table with iodine value ranges for all oils to assist you in determining whether your plant oil is likely to exhibit heat sensitivity:
Botanical/Plant Oil | Iodine Value |
85-95 | |
Acai Fruit Oil | 60-90 |
Ahiflower Oil | N/A |
Allanblackia Oil | 35-39 |
Amaranth Oil | 100-140 |
Andiroba Oil | 65-75 |
Annato Oil | 75-94 |
Apple Seed Oil | 80-85 |
Apricot Kernel Oil | 104-112 |
Arctic Cranberry Seed Oil | 99-110 |
Argan Oil | 96-99 |
Arugula Oil | 137 |
Arnica Oil | 80-140 |
Avellana Oil | 137-147 |
Avocado Butter | 60-80 |
Avocado Oil | 65-95 |
Babassu Oil | 10-17 |
Bacuri Oil | 50-65 |
Balanites Oil | 98-104 |
Baobab Oil | 76-78 |
Basil Seed Oil | 184-198 |
Bitter gourd oil | 90-120 |
Black Cumin Oil | 107-123 |
Black Currant Seed Oil | 160-175 |
Blackberry Seed Oil | 150-190 |
Black Raspberry Seed Oil | 150-190 |
Blueberry Seed Oil | 130-175 |
Borage Seed Oil | 140-155 |
Boysenberry Seed Oil | 121 |
Brazil Nut Oil | 90-110 |
Broccoli Seed Oil | 90-120 |
Buah Merah Oil | 45-75 |
Buriti Oil | 50-75 |
Cabbage Seed Oil | n/a |
Cacay Seed Oil | 110-150 |
Calabash Seed Oil | 100-115 |
Calendula Seed Oil | 112-145 |
Calamus Oil1 | Essential Oil |
Camelina Seed Oil | 124-153 |
Camellia seed oil | 80-87 |
Carrot Seed Oil | 137-138 |
Cashew Nut Oil | 100-119 |
Castor Oil | 81-91 |
Chaulmoogra Oil | 98-103 |
Cherry Kernel Oil | 95-115 |
Cherry Seed Oil | 95-115 |
Chia Seed Oil | 190-199 |
Chilean Hazelnut Oil | 88-100 |
Chilly Seed Oil | essential oil |
Chokeberry Seed Oil | 50-140 |
Chufa Seed Oil | 82 |
Cloudberry Seed Oil | 150-190 |
Coconut Oil | 7-10 |
Cocoa Butter | 33-42 |
Coffee Seed Oil | 76-101 |
Coriander Seed Oil | 88-102 |
Corn Oil | 103-131 |
Cottonseed Oil | 101-107 |
Cranberry Seed Oil | 140-180 |
Cucumber Seed Oil | 110-140 |
Cupuacu Butter | 40-50 |
Custard Apple Seed Oil | 90-130 |
Daikon Radish Seed Oil | 90-120 |
Date Seed Oil | 75-125 |
Dhupa Seed Oil | 36-43 |
Dragon Fruit Oil | 50-120 |
Echium Seed Oil | n/a |
Elderberry Seed Oil | 170-190 |
Emu Oil | 81 |
Evening Primrose Oil | 147-155 |
Fenugreek Oil | 100-145 |
Fig Seed Oil | n/a |
Flaxseed Oil | 170-204 |
Goji Seed Oil | n/a |
Grapeseed Oil | 123-143 |
Gromwell Root Oil | essential oil |
Guanabana Oil | 75-1105 |
Guava Seed Oil | 125-144 |
Hazelnut Oil | 83-90 |
Hemp Seed Oil | 143-166 |
Hibiscus Seed Oil | n/a |
Hinoki Oil | essential oil |
Illipe Butter | 25-40 |
Jatropa Seed Oil | 82-98 |
Jojoba Oil | 78-90 |
Kamala Seed Oil | 166 |
Karanj Oil | 80-90 |
Karkar Oil | n/a |
Kapok Oil | 86-110 |
Kiwi Seed Oil | 180-220 |
Kokum butter | 34-40 |
Kombo Butter | 15-25 |
Kpangnan Butter | 35-55 |
Kukui Nut Oil | 130-175 |
Kusum Oil | 50-60 |
Laurel Berry Oil | 60-85 |
Lettuce Seed Oil | n/a |
Licuri Oil | n/a |
Lime Seed Oil | 105-120 |
Lingonberry Oil | 150-190 |
Loofah Seed Oil | 90-120 |
Lunaria Seed Oil | n/a |
Macadamia Nut Oil | 74-76 |
Macauba Seed Oil | n/a |
Mafura Butter | 60-80 |
Mahlab Oil | n/a |
Mahua Seed Oil | 58-70 |
Mango Butter | 40-60 |
Mangosteen Oil | 65-90 |
Manketti Oil | 120-140 |
Maqui Berry Oil | 110-130 |
Marroti Oil | 92-103 |
Marula Oil | 70-80 |
Meadowfoam Seed Oil | 90-102 |
Milk Thistle Seed Oil | 90-120 |
Monoi Oil | 25-50 |
Moringa Oil | 65-72 |
Mobola Plum Oil | n/a |
Mowrah Butter | 38-40 |
Murumuru Butter | 10-15 |
Mustard Seed Oil | 65-85 |
Niger Seed Oil | 125-135 |
Noni Seed Oil | 9 |
Oat Seed Oil | 82-100 |
Oiticica Oil | n/a |
Ojon Oil | 50-70 |
Okra Seed Oil | 111-180 |
Olive Oil | 78-90 |
Palash Seed Oil | 65-85 |
Palm Kernel Oil | 14-21 |
Palm Oil | 49-55 |
Pastel Seed Oil | n/an |
Papaya Seed Oil | 70-80 |
Parsley Seed Oil | essential oil |
Passionfruit Seed Oil | 130-145 |
Pitaya Seed Oil | 131 |
Peach Kernel Oil | 94-110 |
Peanut Oil | 85-90 |
Pear Seed Oil | n/a |
Pecan Oil | 97-120 |
Peony Seed Oil | 162-190 |
Pequi Seed Oil | 46-55 |
Perilla Seed Oil | 196-206 |
Pilu Oil | 12-20 |
Pine Nut Oil | 137-141 |
Pisa Oil | 85-109 |
Pistachio Nut Oil | 86-101 |
Plum Kernel Oil | 90-120 |
Pomegranate Seed Oil | 210-250 |
Pomifera Seed Oil | n/a |
Poppy Seed Oil | 133-197 |
Praxaci Oil | 90-105 |
Prickly Pear Seed Oil | 100-130 |
113-134 | |
Quinoa Seed Oil | 118-1501 |
Ramtil Oil | n/a |
Rapeseed Oil | 94-120 |
Rhatany Oil | n/a |
Rice Bran Oil | 89-108 |
Rosehip Seed Oil | 152-169 |
Rubber Seed Oil | 132-148 |
Sacha Inchi Oil | 183-199 |
Safflower Oil | 140-150 |
Sal Butter | 35-45 |
Sandalwood seed Oil | 100-123 |
Saw Palmetto Oil | 40-50 |
Sapote Oil | 60-70 |
Sea Buckthorn Berry Oil | 60-70 |
Sea Buckthorn Kernel Oil | 130-200 |
Sesame Seed Oil | 100-120 |
Sisymbrium oil | 96-106 |
Shea Butter | 50-70 |
Shea Butter var nilotica | 75-90 |
Shea Oil | 75-90 |
Shikonin Seed Oil | n/a |
Sorghum Oil | 108-122 |
Souchet Oil | 65-95 |
Soursop Oil | 75-105 |
Soybean Oil | 125-140 |
Strawberry Seed Oil | 175-190 |
Sunflower Oil | 118-145 |
Sunflower Seed Oil | 118-145 |
93-105 | |
Tamanu Oil | 99-108 |
Tamarind Seed Oil | 75-118 |
Taramira Seed Oil | essential oil |
Thumba Seed Oil | 118-122 |
Tobacco Seed Oil | 125-154 |
Tomato Seed Oil | 107-125 |
Touloucouna Oil | n/a |
Tucuma Butter | 10-30 |
Tucuma Oil | 75-90 |
Tung Oil | 160-175 |
Ucuuba Butter | 12-15 |
Walnut Oil | 135-151 |
Watermelon Seed Oil | 97-128 |
Wheat Germ Oil | 115-128 |
Wolfsberry Oil | n/a |
Ximenia Oil | 65-95 |
Yangu Oil | 85-105 |
The heat sensitivity of other Botanical extracts
Butters
Butters contain high saturated fat content and low iodine levels. They are not heat sensitive, have high heat stability, and are ideal for adding to the heated phase.
Essential Oils
Essential oils are derived from plant matter via steam distillation. While the production process is heated, the resulting essential oils are heat sensitive due to their fragile components and volatility, thus only add them to your formulation during the cool down phase.
Hydrosols
Hydrosols are a byproduct of the essential oil distillation process; therefore, they have already been exposed to heat. They include trace levels of essential oils as well as other non-essential components. While some authorities believe that because they have already been heated, further heating in formulations should have no effect on their qualities, others prefer not to heat their hydrosols for fear of them evaporating and losing some of their properties; therefore, it is up to the user's decision.
Glycerites
Glycerites are botanical extracts that use glycerin as a solvent to absorb the botanicals' properties. While glycerin is heat stable, the properties of the botanicals are likely to be more delicate, thus including the glycerites in your cool-down step.
As stated in the article, the iodine value given is not an absolute science; it is just a guide for you to familiarize yourself with plant oils and become knowledgeable on how to properly heat and use your delicate oils without destroying their wonderful properties. This list is not only for the seasoned formulator but also for beginners and enthusiastic diYers, as we all deserve to create beautiful formulations that will be stable and offer all the great benefits of the natural ingredients used.
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