Want Better Roasted Vegetables? Stop Doing This One Thing

Swetha Sivakumar

September 2, 2025 at 11:28 PM

In a Nutshell

For the deepest browning and best flavor, roast vegetables on a bare, oiled tray; use foil if you want easier cleanup, and save the parchment for cookies.

Golden, crisp, burnished edges are the crowning glory of roasted vegetables. A tray of sweet potatoes with a deep caramelized crust, or broccoli that's seared and browned in just the right spots, is my culinary dream. Browning isn't just about looks; it also means deeper flavor, thanks to the sweet and nutty notes from the Maillard reaction.

But consistently achieving this result can be challenging. Even if you season and oil your vegetables well, the way you set up your baking sheet can affect how much browning you get. Many recipes call for lining the tray with parchment paper or aluminum foil to minimize mess and save you from scrubbing later. And sure, as someone who also has to face the pile of dirty dishes at the end of the night, I get the appeal. But does lining your baking sheet when roasting actually hold your vegetables back from achieving their best, crispiest selves? Does the convenience of an easier clean-up outweigh the potential flavor loss?

I decided to test it. My goal was simple: Find out how much of an impact different tray linings have on browning and texture when roasting vegetables. I set up side-by-side comparisons, ran the experiments multiple times with different vegetables, and paid close attention not just to the appearance of the vegetables while trying to figure out what was happening on a scientific level. Here's what I found.

Why Line a Baking Sheet When Roasting?

Before diving into the results, it helps to think about what each of these surfaces actually does in the oven. A bare aluminum baking sheet is the baseline -- it heats up quickly, conducts that heat efficiently, and makes direct contact with the food. Aluminum foil also conducts heat very well, nearly as efficiently as the tray itself, though it adds not only a thin layer of metal between the food and the pan but also a small layer of space between the foil and the pan. Parchment paper, meanwhile, is essentially cellulose fiber that's been treated with silicone or Quilon to make it nonstick and heat-resistant. It's very thin, about a tenth of a millimeter, but compared to foil, it's a poor conductor of heat (and also introduces space between the paper and the pan itself).

To put numbers on it, parchment has a thermal conductivity of about 0.18 W/m·K, while aluminum foil comes in around 237 W/m·K. In other words, foil transfers heat over a thousand times more efficiently than parchment.

That difference matters because the oven itself isn't a particularly efficient heat transfer system. As Harold McGee explains in On Food and Cooking, air is less than one-thousandth as dense as water, which means far fewer collisions with the surface of your food. The oven's dry air does help dehydrate surfaces and encourage browning, but the direct contact between hot metal and food is a critical part of that "oven sear." Add a layer of parchment, and you've just placed an insulator between the heat source and your vegetables.

Still, lining isn't always a bad thing. Sometimes, slowing heat transfer is the goal, as with cookies or cakes, where evenness and moisture retention are more important than aggressive browning. But for roasting vegetables, where crispness and caramelization are what we're after, I suspected parchment is holding us back.

Putting It to the Test

To see how much tray linings really matter, I ran a series of side-by-side experiments, comparing bare metal, foil, and parchment. Each test looked at a slightly different angle. The first was with water, and was designed to isolate heat transfer. Then, I ran tests by roasting typical vegetables like broccoli, zucchini, and carrots. Finally, I tried roasting sugar-rich vegetables like sweet potatoes and butternut squash, which are especially prone to caramelization and charring.

Test 1: Water Evaporation

I started simple, with water, to get a visual read on heat and moisture transfer. I divided a baking sheet into three sections -- bare, parchment-lined, and foil-lined -- added one tablespoon of water to each, and baked the tray in a 425°F oven.

The results were clear. The water on the unlined section evaporated first, followed closely by the foil. The parchment lagged noticeably behind, with droplets still clinging to its cooler surface even after the others had dried up. I repeated the test, rotating positions to rule out hot spots, and got the same outcome. This confirmed parchment was indeed running cooler and trapping more moisture at the surface.

Test 2: Broccoli, Zucchini, and Carrots

Next, I moved to vegetables that most of us roast regularly. Broccoli florets, sliced zucchini, and carrots were placed on the three surfaces, roasted at 425°F for 20 minutes, and flipped halfway through.

The difference was noticeable as soon as I opened the oven. On bare metal, the broccoli and carrots had the deepest browning. Foil performed almost as well, though it held on to slightly more moisture. The parchment side lagged again. There was less color, less crispness, and more limp texture. With zucchini, the unlined section softened and caramelized the most (in a good way), while the parchment side stayed paler and firmer.

Test 3: Butternut Squash and Sweet Potatoes

Finally, I tested starchy, sugar-rich vegetables that are especially good indicators of caramelization. I roasted butternut squash and sweet potatoes at 425°F for 30 minutes, flipping at the 15-minute mark.

Once again, the parchment-lined section showed the least browning. With sweet potatoes in particular, the difference was striking: The unlined and foil sections developed charred, candy-like edges from direct contact with the hot surface. In contrast, the parchment section looked underdeveloped.

Summary of Results

Across all three trials, the pattern was consistent: Vegetables on bare metal browned and crisped the most, foil came in a close second, and parchment lagged. The water test showed parchment slowed evaporation, the mixed-veg test revealed less color and limp texture, and the sweet potato and squash test highlighted how much caramelization you lose when food isn't in direct contact with hot metal. In short, parchment consistently ran cooler, trapped more moisture, and delivered weaker browning compared to foil or an unlined tray.

The Science Behind the Results

Based on the tests, the vegetables on parchment consistently ran cooler than those on foil or bare trays. Steam hitting the cooler parchment surface condensed rather than evaporated, creating a thin moisture barrier at the food's base. Only after the parchment heated up enough did that trapped moisture evaporate again, by which time valuable browning had already slowed down.

On metal surfaces, on the other hand, heat is transferred quickly and efficiently, encouraging rapid evaporation and direct caramelization wherever the food makes contact with the tray. That's why the unlined and foil-lined vegetables browned faster, crisped more deeply, and developed those candy-like edges on sweet potatoes.

It's important to note that vegetables will eventually brown on parchment, it just takes longer, since the insulating layer dulls the intensity of the heat, which will likely lead to the food turning mushy or drying out on the top surface. When the goal is crisp, deeply roasted flavor, parchment holds you back while bare metal (or foil, in a close second) delivers the best results.

Parchment vs. Foil: Where Each Shines

By this point, the tests made it clear: Parchment consistently slowed browning compared to both bare metal and foil. But lining choices aren't only about browning; convenience, cleanup, and how different foods interact with the surface matter, too. And that's where parchment and foil start to diverge.

Nonstick: Parchment is unmatched when it comes to easy release. Vegetables, pastries, or cookies slide right off without tearing, and you can reserve all your oil for coating the food instead of greasing the pan. Foil, by contrast, is notorious for clinging to starchy or protein-rich bits, often tearing when you try to lift or scrape them away.

Nonreactive: Parchment is chemically inert and safe with acidic ingredients like tomatoes, citrus, or vinegar. It won't react or affect flavor. Foil, however, can react with those same ingredients, leaving behind off-flavors, discoloration, or even corrosion of the foil surface.

Heat limits: Most kitchen parchment is rated up to 425-450°F. While its silicone coating can technically tolerate higher temperatures, the paper itself begins to scorch, dry out, and turn brittle at those extremes. Aluminum foil, on the other hand, is stable at far higher temperatures -- its melting point is over 1,200°F (660°C) -- so it can handle everything an oven or grill can throw at it.

So parchment excels when you need a reliably nonstick, flavor-neutral surface for delicate or acidic foods, or when you simply want to save yourself from scrubbing later. Foil is a better choice for high-heat cooking, offering browning results similar to those of bare metal, although it comes with a slight risk of sticking.

Final Takeaway

For the best browning and crispest texture, nothing beats roasting directly on a bare, oiled tray. If you want an easier cleanup, foil comes close and delivers nearly the same results. Parchment, though convenient and practical in plenty of other contexts, consistently holds vegetables back from achieving their deepest, roasty flavor. When golden, caramelized edges are the goal, skip the parchment. A few extra minutes of scrubbing are worth the payoff.

Read the original article on Serious Eats