Why You Shouldn't Worry If Aluminum Foil Discolors In The Oven

Whether you need to cover a casserole before popping it in the oven, line a cookie tray, or wrap up leftover slices of pizza, aluminum foil is one of those trusty kitchen staples that's always good to have on hand. It's food-safe, durable, incredibly versatile, and time-tested, having proven its usefulness in home kitchens for nearly a century. Aluminum foil is such a ubiquitous, must-have kitchen staple that it's hardly ever worth giving a second thought. That might change suddenly if you pull a cheesy, bubbling pan of lasagna out of the oven and notice that the aluminum foil covering the dish has turned dark and discolored. While it could look like cause for concern, the darkening and changes to the color are totally harmless.

The kitchen mainstay we've all come to rely on is made from alloy metal rolled thin and blended with trace amounts of silicone and iron to fortify and strengthen the material. What you're seeing is simply the result of moisture from the food interacting with the foil and creating a buildup of aluminum oxide. The dark brown or black discoloration on foil that has been in a hot oven is just the naturally occurring aluminum oxide becoming more noticeable to the naked eye via the increase in moisture from the food it's in contact with.

You needn't sweat if that sheet of foil picks up some discoloration after a while in the oven, but since it's designed to withstand high temperatures and direct heat, there are still some safety tips and best practices worth bearing in mind. While the use of aluminum foil in the oven, grill, and even air fryer is perfectly fine, never put it in the microwave, as this could cause sparks and even start a fire, not to mention damaging the appliance. You'll also want to skip the supposed trick of lining the bottom of the oven with foil. This can detract from the oven's ability to heat and cook food and also cause cosmetic scratches and damage. 

If you've been wondering if aluminum foil and tin foil are the same thing or if these safety tips apply to both, yes and yes! The names are sometimes still used interchangeably for the same product, but all rolls you can buy at the store these days are made from aluminum — tin was routinely used up until around WWII, at which point aluminum replaced it permanently. Like a roll of paper towels or a can opener, aluminum foil is one of those tools that no kitchen is complete without.