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Reposting a little description of what occurs when seasoning cast iron. From a cast iron group that accepts people that were banned from "the only way to do it" groups. 🍳EnjoyHere's a short essay I wrote that I shared to the group a couple weeks ago**The Science of Seasoning Cast Iron**TL;DR - When seasoning your cast iron, you should choose an oil with a high smoke point and high polyunsaturated fat content such as grapeseed oil or refined soybean oil and heat it just below the smoke point for an hour or so. Seasoning your cast iron pan is not just an art; it's a science. This short essay will delve into the science behind cast iron seasoning, exploring what seasoning is, how it adheres to the pan, the ideal seasoning temperature, and how to select the best oil for the job. Whether you're new to cast iron or a seasoned pro, understanding the science can help you achieve the perfect seasoning. I spent a long time sifting through scientific papers about the chemistry behind seasoning, so I hope this information is beneficial for the community at large. What Is Seasoning/Polymerization?- Seasoning is the process of coating your cast iron in a super thin layer of oil and heating it to the point of polymerization. Polymerization is where the unsaturated fats in the oil change form to create a hard plastic layer that prevents food sticking to it and also protects the pan from rusting. Unsaturated fats are made up of atoms held together with double bonds. For polymerization to occur these double bonds in the oil need to be broken and rearranged to form long chains of Carbon-Carbon bonds which is what your seasoning is made up of. Heat is needed to create the strong Carbon-Carbon bonds. As the oil is heated, the double bonds are broken and they reorganize themselves into covanently bonded Carbon-Carbon bonds. They key to maximizing these bonds and creating the best possible seasoning is to carefully regulate the temperature your pan is heated to. How does seasoning stick to the pan? - There are two reasons that the seasoning will stick to your pan. The first, and most commonly discussed reason is that the oil hardens between the grooves in the rough surface of the iron. Now when I say rough surface, I'm not talking about the iconic "bed liner" texture of Lodge pans, but rough on a microscopic level. Even if you sand or grind a pan down to make it appear smooth, on a microscopic level the iron is still incredibly rough with grooves and pits everywhere which is where the oil can get into and harden to help secure your seasoning to the pan. Think of it like Velcro. When pressed together the hooks and loops intertwine making it difficult to pull apart. A similar thing is happening between the hard seasoning layer and the pan. - The second, and more important reason that your seasoning sticks to your pan is that some of those Carbon-Carbon bonds that the oil makes to form a polymer, it also makes with the carbon atoms in the iron of your cast iron pan. These covalent bonds literally bond your seasoning to your pan on a molecular level and make the cast iron and the seasoning one homogeneous layer. If a pan is properly seasoned, you will achieve both physical sticking like Velcro, and chemical bonding to the very iron that makes up your pan creating an incredibly tough nonstick layer. So how should you heat your pan?- First you need to know the smoke point of your seasoning oil. Smoke point is the temperature where your oil starts to break down and emit smoke. This information can be found with a quick Google search of the type of oil you are using. Also note that refined oils usually have a higher smoke point than their unrefined versions, so make sure you know which one you have. - Often I see people say the best way of seasoning involves heating your pan up above the smoke point to make sure the oil completely polymerizes, but that is actually bad advice. When you heat your oil up above the smoke point, the oil begins to degrade and not only limits the amount of Carbon-Carbon bonds that can form, but also burns the oil introducing imperfections leading to a brittle layer of seasoning that is prone to flaking off the pan. - On the other hand, at temperatures too far below the smoke point, the oil is relatively stable, and the breakdown of double bonds is a much slower process. Some double bonds may still break due to heat, but the polymerization process, which involves the formation of long chains of molecules, is less likely to occur at lower temperatures. Instead, the oil will undergo processes like isomerization and oxidation which won't create that tough nonstick coating you are looking for and can also leave your pan feeling sticky.- The way to achieve the absolute best seasoning is to heat the pan as close to the smoke point of your oil as possible without exceeding it. This will allow the maximum amount of Carbon-Carbon bonds to form and create a super tough nonstick seasoning without breaking down the oil and introducing imperfections into the coating. I usually heat my pan 5-15°f under the smoke point of the oil I'm using. For example, if your seasoning oil has a smoke point of 420°f, you should ideally aim to heat your pan to around 400-415°f for around an hour. Just make sure to watch your pan as you heat it and lower the temperature if you see smoke because residential ovens can often be off temperature by as much as 50°f, and oils smoke points can vary slightly based on manufacturer process and age of the oil. If you want to get really serious, get a separate oven thermometer to double check the temperature of your oven. Picking the best oil- Lastly we need to discuss the different types of oil, and what makes a good seasoning oil.There are 3 main types of fats found in cooking oil; saturated fats, monounsaturated fats, and polyunsaturated fats (there are also trans fats, but they are banned from food products in many countries due to safety concerns). - Saturated fats don't contain any double bonds, so they won't polymerize to form seasoning. You should avoid oils with a high content of saturated fat as seasoning oils. - Monounsaturated fats contain one double bond in each molecule, so they will polymerize and form a seasoning layer, but because they only have one double bond, your seasoning won't be as strong. You can use oils with a high content of monounsaturated oil for seasoning, but it's not your best option. - Polyunsaturated fats have multiple double bonds in each molecule meaning they can form many more Carbon-Carbon bonds than monounsaturated fats giving you the strongest, and best seasoning layer. - The amount of polyunsaturated fat isn't everything however... You also need to choose an oil with a high smoke point preferably over 400°f. The higher the smoke point of your seasoning oil, the more resistant to break down your seasoning layer will be under high heat cooking. Some oils such as flaxseed oil just won't make a good seasoning oil despite its high polyunsaturated fat content due to its low smoke point of just 225°f which will cause it to break down and flake off during higher heat cooking. Some of the best oils you can use for seasoning are refined grapeseed oil and refined soybean oil. Per Tbsp, refined grapeseed oil has a whopping 10g of polyunsaturated fat, 2.5g of monounsaturated fat, and only 1.5g of saturated fat with a high smoke point of around 420°f. Refined soybean oil has 8g of polyunsaturated fat, 3g of monounsaturated fat, only 2g of saturated fat and has an impressive smoke point of around 450°f. I personally use refined soybean oil as my seasoning oil of choice due to its slightly higher smoke point and it being significantly cheaper to buy than grapeseed oil, but any oil that meets the criteria I described above will make a fantastic seasoning oil.I've put in a ton of work researching and compiling all this information, so I hope it was interesting and beneficial to at least a couple people. Please let me know if you have any questions or want more information on a particular topic. Thanks for reading!