There’s a lot to love about cast iron pans, but one of the material’s greatest virtues is that it can be seasoned, and re-seasoned almost indefinitely, potentially extending its life and restoring its non-stick qualities for decades, or even generations.
We’ve discussed how you should go about seasoning your skillet, but one question always sparks vigorous debate in culinary circles: what oil should you use to do it?
What is seasoning?
Before you choose a seasoning oil, it can be useful to know what exactly seasoning is. Essentially, it’s a layer of baked-on oil or fat that hardens and adheres to your pan through a process called polymerization. This layer of seasoning protects the metal underneath from rust (the kryptonite of cast iron), and also imbues the pan with nonstick properties.
Basically any time you use your pan, you’re doing things that can either be restorative to your seasoning, or damaging to it. Any time you cook with oil or fat, you’re probably repairing and enhancing the seasoning that’s already on your pan as those oils polymerize during the cooking process. However, any time you do things like use dish soap (in large quantities), leave standing water in a pan, cook with acidic foods, or scrape your pan with metal utensils, you’re chipping away at your seasoning. Sometimes, those damaging actions outweigh the restorative ones to the point that food will start sticking to the pan, and you might even notice some spots of rust. At this point, it’s time to do a thorough re-seasoning.
What to look for in a seasoning oil
First of all, don’t be scared about screwing this up: name a cooking oil, and there’s probably a large contingent of people out there who swear it’s the best option for seasoning. The fact is, basically any oil you use is going to make your pan more non-stick, and protect it from rust. They’re (almost) all good! Some will just form a somewhat more durable barrier, or take less time to polymerize.
The most important thing to look at here is an oil’s smoke point. While you generally don’t want your oil to smoke when cooking, it’s exactly what you’re going for when you’re seasoning a pan. Smoke means your oil is polymerizing, and hardening to become part of your seasoning. Seasoning your pan at a significantly higher temperature than your oil’s smoke point won’t necessarily result in a better finished product, but it will speed up the process, which makes oils with lower smoke points appealing.
In this chart from Lodge, you can see that flaxseed oil has a far lower smoke point than any other common cooking oil, but most ovens will be able to exceed the smoke points of most oils, which is what ultimately matters at the end of the day; higher temp oils will just require more patience.
Saturated vs. unsaturated fats
All oils contain both saturated and unsaturated fats, but it’s the unsaturated fats that will more easily polymerize and bond to the molecules already present in your pan. Again, with enough heat and time, it’s hard to screw up cast iron seasoning no matter which oil you choose, but all things being equal, you’ll get better results with an oil with a higher makeup of unsaturated fats.
Many people swear by the lard and bacon grease that their parents and grandparents used for seasoning, because those types of fats were widely and cheaply available in decades past. However, both of those oils have a high percentage of saturated fats compared to more modern cooking oils (which, pro-tip, is why they solidify at room temperature), so there are better options available.
So, which oil should I use to re-season my cast iron?
Safflower oil, flaxseed oil, grapeseed oil, and canola oil are all very low in saturated fats, and all would be great options for re-seasoning your pan. If you have one of them in your pantry, go ahead and use it! It won’t even take more than a few tablespoons.
If you need to buy an oil for this project, flaxseed has the lowest smoke point and will probably take the least time, but it’s not cheap. Safflower oil has a high smoke point of about 500 degrees, but would be a fine option if you’re sure your oven can get hot enough. Grapeseed and canola oils both have smoke points in the low 400s, and canola oil will usually be the cheapest of the bunch. All four will give you great results, and should keep your pan slippery and rust-free for years to come, as long as you remember to clean it properly.