The rough and blackened appearance on the bottom of a well-seasoned cast-iron skillet can be caused by a few factors:
Cooking Residue and Food Debris: Over time, even with proper seasoning, cooking residues and food debris can accumulate on the bottom of the skillet. This buildup can create a rough texture and cause the skillet to appear blackened. The seasoning on the cooking surface may remain intact, but the bottom can still get dirty and lose its smoothness.
High Heat Cooking: Cooking at very high temperatures or using intense heat sources, such as open flames or high-heat grills, can cause the bottom of the skillet to become blackened. The extreme heat can lead to the breakdown of the seasoning and create a layer of carbon buildup.
Uneven Heating: Uneven heating can be a factor, especially if the skillet is used on a gas stove without a proper heat diffuser or on an uneven heat source. The areas that receive more direct heat might become blackened due to excessive heat exposure.
Exposure to Moisture: If the skillet comes into contact with excessive moisture or is stored in a humid environment, the bottom can develop rust and oxidation, leading to a rough and blackened appearance.
To address these issues and restore the bottom of your well-seasoned cast-iron skillet, you can follow these steps:
Clean and Scrub: Start by thoroughly cleaning the skillet, both on the cooking surface and the bottom, using warm soapy water and a soft brush or sponge. Avoid using abrasive tools that could damage the seasoning.
Rinse and Dry: Rinse the skillet well, ensuring no soap residue remains, and dry it completely using a towel.
Re-Season the Bottom: Apply a thin layer of oil to the bottom of the skillet, just as you would season the cooking surface. Use an oil with a high smoke point, such as vegetable oil or flaxseed oil. Wipe off any excess oil with a clean cloth.
Heat in the Oven: Place the skillet upside down in the oven and heat it at a high temperature (around 400-450°F or 200-230°C) for about an hour. This process will help the oil polymerize, creating a new protective layer on the bottom.
Cool and Store: Let the skillet cool in the oven before removing it. Afterward, store the skillet in a dry place to avoid moisture-related issues.
Regularly maintaining your cast-iron skillet, including cleaning and re-seasoning as needed, will help prevent excessive buildup and keep the bottom smooth and protected. Remember that the bottom may never be as smooth as the cooking surface due to the differences in wear and usage, but proper care will still ensure its functionality and longevity.