The Surprisingly Common Mistake You’re Making With Roasted Vegetables

Roasted vegetables are as straightforward as side dishes come. But to line with foil or not to line with foil? That's the question.

Making roasted vegetables is an easy, hands-off way to get tons of different types of veggies on the table. Tossed with oil and salt and roasted on a baking sheet in a hot oven, roasted vegetables of all kinds—carrots, sweet potatoes, cauliflower, broccoli, squash—are about as simple as side dishes come. Who knew there was any controversy?

The other night I mentioned (in my Instagram story) that I never line my sheets with foil when roasting vegetables. In fact, I semi-dramatically crossed my arms in front of me and said “do NOT line with foil when roasting vegetables.” But after the fact, at least a dozen people DM’d me to ask why. They always lined when roasting for easy cleanup. Why don’t I?

In my experience, lining a sheet tray with foil prevents vegetables from taking on that deep golden brown that makes them so irresistible. There’s some real science behind this. Something about (heat capacity) x (mass) x (temperature change), etc. Aluminum foil is a really good heat conductor. But because it’s so thin it cools off fast, too. I knew what I had seen, and I knew I wasn’t making it up. But there was only one way to be sure: A good old fashioned side-by-side test.

Employing everything I remembered about the scientific method from eighth grade chemistry, I set up my experiment with as few variables as possible:

  • I started with two identical quarter sheet trays. I lined just one with a single layer of aluminum foil.
  • We happened to have two bags of carrots in the test kitchen fridge so I divided them by weight—the only truly efficient way— peeled them, and chopped them into similarly-sized pieces.
  • I tossed each tray of carrots with 1 TBSP olive oil and 1/2 tsp kosher salt and prepared to roast.

Meanwhile, I’d preheated the oven to 425°F—hot enough to get things nice and brown but with a little wiggle room in case you’re in the bathroom or something when the timer goes off. I placed the sheets side by side on the middle rack of the oven and set a timer for 10 minutes.

When the timer went off and I opened the oven door, there was some serious sizzling going on. Just as I suspected, the carrots on the unlined tray were already picking up some color. The carrots on the lined tray were not (DP grabs chalk, places one tick in her own column). I rotated the sheets from left to right and back to front and closed the door.

After another 10 minutes the evidence was in. The carrots on the unlined sheet were more deeply browned, slightly sweeter and more tender (two ticks). The carrots on the lined tray did take on some color, just not quite as much. And they weren’t quite as tender. And, well, fine, they were pretty good if a tad undercooked.

The verdict? It’s your call. I’m still anti-lining: less work on the front end, less trash in the landfill, and a more delicious end product. But if it’s the dishes that get you down, go ahead and line, just add a few extra minutes to your roasting time. In the end, pick your battle. Just don’t say I didn’t warn you.

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