In our tests over the years, we’ve used a variety of neutral oils to season cast iron, including canola (rapeseed), soybean, sunflower, linseed (flax), grapeseed, refined coconut, vegetable oil blends, and vegetable shortening. They all work well to create a durable seasoning. According to Eric Decker, professor and department head of the Department of Food Science at the University of Massachusetts Amherst, oils with increased levels of unsaturation will oxidize faster and make more polymers. So avoid using saturated fats, such as butter, which won’t season properly.
