Food sticks to new cast iron pans but not to well-seasoned old ones due to the formation of a natural non-stick surface known as "seasoning." Seasoning is a layer of polymerized oil that fills the pores and microscopic irregularities on the surface of the cast iron, creating a smooth, non-stick coating.
When a cast iron pan is new or not properly seasoned, its surface is relatively rough and porous. This allows food to adhere to the surface, leading to sticking and making cooking and cleaning more challenging. However, as the pan is used and undergoes the seasoning process, several changes occur:
Polymerization: The oils or fats used for seasoning undergo a process called polymerization. When exposed to heat, the fats break down and bond together, creating a hard, slick surface that becomes increasingly non-stick with each use.
Filling pores: As the seasoning builds up over time, it fills the pores and imperfections on the cast iron's surface. This results in a smoother cooking surface, further reducing the chances of food sticking.
Carbonization: The seasoning layer becomes darker and takes on a carbonized appearance after repeated heating and cooking. This is a sign that the seasoning is forming a durable and non-stick layer.
Flavors and aromas: The seasoning also imparts a unique flavor and aroma to the food, enhancing the overall cooking experience.
As the seasoning layer develops and the pan is used regularly, it becomes more effective at preventing food from sticking. Properly seasoned cast iron pans can eventually achieve a nearly non-stick surface that rivals commercial non-stick cookware. Additionally, the more you use a well-seasoned cast iron pan, the better it becomes at cooking and releasing food effortlessly.
It's essential to maintain the seasoning by avoiding harsh cleaning methods, using mild detergents, and reapplying a thin layer of oil after each use to preserve the non-stick properties. With proper care, a well-seasoned cast iron pan can last a lifetime and provide excellent cooking performance.