We recently put a batch of pristine new sheets into rotation in the test kitchen and suddenly found that our recommended cooking times weren’t getting the job done. What happened?
As we used our shiny new baking sheets, we noticed that garlic bread was pallid and limp, and butternut squash emerged from the oven looking steamed instead of roasted.
We know that dark-colored pans absorb and transfer heat more efficiently than lighter-colored pans. Could the same be true of dull pans, even if they are roughly the same color as a shiny new version?
To find out, we placed gleaming new sheets and dull older ones in the oven with thermocouples attached to record the rates at which they heated.
Sure enough, the older sheets heated rapidly, reaching just over 400 degrees in 15 minutes. The shiny new sheets were slower to heat, hitting only 350 degrees in the same amount of time. And they never got as hot as their duller counterparts, maxing out at 385 degrees after more than 30 minutes, meaning these sheets would be far less effective for browning food.
So if your baking sheet has lost its luster, you should celebrate, not mourn.