The Most Delicious Fats Are Also The Worst For Seasoning Cast Iron

There's something wonderful about the sizzle and the smoky, rich aroma of bacon grease in a cast iron skillet. And don't even get us started on the tropical sweetness of coconut oil. These fats might make some meals taste better, but they also happen to be not the best oils for seasoning your cast iron skillet.  When we talk about seasoning a cast iron pan, we don't just mean flavor. In cast iron care, "seasoning" refers to the hard, protective layer that forms when oil is heated past its smoke point and polymerizes, bonding to the metal. This coating keeps your skillet nonstick and rust-resistant. Saturated fats like coconut oil have a lower smoke point and don't polymerize as effectively. That means they're more likely to leave behind a sticky, uneven residue that flakes over time, and that's not what you want. You want to reap the unique benefits of cooking with a cast iron.

You might get a short-term shine, but it won't hold up after a few rounds of cooking and washing. Worse, you could end up with a gummy layer that traps moisture and odors, basically the opposite of what you want in a good seasoning. And while it might seem logical to use the same fat you're already cooking with to build your skillet's seasoning, that logic doesn't hold up in practice. Flavor and function are two very different things when it comes to oil chemistry.

Let's talk about the science behind it. The best oils for seasoning a cast iron skillet are high in unsaturated fats, especially polyunsaturated fats. These fats have multiple double bonds in their molecular structure, making them more reactive when heated. That reactivity helps them undergo polymerization, transforming from a liquid into a durable, hard coating that bonds to your skillet's surface.

Saturated, fat-rich oils like coconut oil (which is about 90% saturated) lack the double bonds necessary for this conversion. They stay soft or sticky rather than forming that slick, protective finish you're aiming for. Lard and bacon grease are also largely saturated, which means they behave the same way. They may work okay for daily frying, but they're not reliable for building a lasting base layer of seasoning.

Even though saturated fats like coconut oil don't go rancid as easily as unsaturated oils, they can still spoil if stored poorly. The same thing goes for animal fats such as lard or beef tallow. So, while grandma swore by bacon grease, science says it might not be the appropriate option for your cast iron. To be clear, research on oil polymerization is still evolving, and the perfect oil for every home cook may depend on factors like oven temperature, application method, and how often you use your skillet. But the general consensus is this: the oils that taste the best are usually not the best at creating a solid, long-term seasoning layer.