The Important Tip To Know If You're Boiling Water In A Cast Iron Pot

Of all the ingredients you shouldn't use with cast iron cookware, water might not be the first thing that comes to mind. But unfortunately, it's true that you shouldn't boil water in a cast iron pan. At least, you shouldn't boil water for extended periods of time at a rolling boil. Doing this can actively break down the pan's seasoning — that nonstick coating you worked so hard to build up.

What you can safely do, however, is keep it quick. Boiling water for 10-15 minutes at a time is unlikely to do much damage. What's more, you can safely boil water or water-based liquids (like soups, stocks, or stews) for up to an hour as long as you keep the heat low enough to maintain a gentle simmer. For thick recipes with minimal water content, like cheese sauces or chili, you can simmer them for longer than an hour without affecting your pan. For the most part, if you really need that water to reach a long, rolling boil, you're better off grabbing a separate stock pot that can handle the task without issue.

The key to cooking with a cast iron pan is keeping it well seasoned. When you season a cast iron pan, you do more than create an aesthetically pleasing patina — the baked-on layer of oil also creates a natural nonstick surface, as well as a protective layer that keeps rust at bay. This protective layer needs to be periodically re-seasoned, especially since it can break down over time due to you cooking with acidic foods (like vinegar or tomatoes), scrubbing too hard when cleaning, or cooking at an excessively high heat. But, it can also break down from regular exposure to boiling water. 

Rapidly boiling water can cause the seasoning to lift from a cast iron pan, not only leaving it vulnerable to rust, but also releasing little black flakes of the seasoned surface into your food. Some folks also boil water in their cast iron pan to clean it, as the hot water can loosen stuck-on food particles. However, this, too, will loosen the seasoning layer over time and cause it to flake off.

If you've found out the hard way that boiling water can damage your pan's seasoning, the good news is there's no reason to worry. You can simply re-season the pan, removing any rust with some steel wool.