Well, a lot of things. The quality of the vegetable. How you slice and dice it. Whether your grill is clean. What temperature it’s at. How much oil you use. How much salt you use. Whether you go above and beyond with something like a lemon squeeze and herb sprinkle.
Today, though, we’re going to focus on how oil affects grilled vegetables. Namely: Vegetable or extra-virgin olive? A quick drizzle or dressing-like marinade? On the grates and on the vegetables, or just one or the other? And actually, is oil necessary at all? The answer to each of these depends on who you ask.
In On Food and Cooking, food science authority Harold McGee writes, “A coating of oil speeds the cooking and improves flavor.” He notes that some vegetables love to be steamed in a package, for gentler cooking and smoky flavor, such as corn in its own husk or potatoes in a foil purse. What’s more, purposefully burning certain vegetables, like eggplants and peppers, is an easy way to remove the skin and add nuanced flavor.
In our grilling book, Any Night Grilling, author Paula Disbrowe recommends oiling the grates before grilling vegetables. She uses vegetable oil and—get this—a fork-speared onion half instead of a brush. She then has you toss your chosen vegetables “with enough olive oil to lightly coat.” Not only does this encourage more browning, but it also means you can generously season the vegetables with salt and pepper, because the seasonings now have something to stick to.
In How to Grill Everything, Mark Bittman agrees with Paula, mostly. He tells you to “brush the vegetable slices with [good-quality extra virgin olive oil], coating them completely.” Clean grates are a must but, interestingly, oiled grates are not. The theory here is that the oil on the vegetables is enough to prevent sticking, so no need to add more oil the situation and risk a burnt-oil flavor.
Cooks’ Illustrated supports this, telling readers that “applying a thin layer of extra-virgin olive oil to vegetables...before grilling encourages even browning and helps prevent them from sticking to the grill grates.”
Our test kitchen director Josh Cohen told me: “I lightly oil veggies before throwing them on the grill. That way, they get a nicer caramelization and char, which translates to more flavor.” He uses olive oil for quick-cooking vegetables and “a high-heat neutral oil like canola or grapeseed oil, because this oil won't burn or turn acrid” for just about everything else.
In Bon Appétit’s The Grilling Book, it varies by vegetable. For example, for asparagus, the editors recommend grilling them dry and drizzling with extra-virgin olive oil afterward. For fennel, they tell you to “brush with oil before putting it on the grill.” Perhaps this is because some vegetables are more prone to sticking than others or need to cook longer. Either way, they recommend oiling the grates with vegetable oil first.
In Six Seasons: A New Way With Vegetables, Joshua McFadden skips the oil altogether. He writes, “Be sure you don't coat your carrots with oil before you grill them; grilled oil just tastes like chemicals to me.” When I reached out to him about this atypical advice, he told me that he came to this method by grilling bread. In one batch, he oiled the grill and bread beforehand and thought it tasted “awful.” In another batch, he grilled the bread dry, then rubbed it with garlic, drizzled olive oil on top, “and it was like heaven.” His vegetables have been following suit ever since.
Our contributor EmilyC also skips straight oil—but uses mayonnaise in its place. In her recipe for Grilled Potato & Green Bean Salad (you really should go make it right now), Emily makes a mayo-based marinade with white miso and Dijon mustard.
"I started experimenting with mayo marinades after seeing Nate Appleton’s Mustard-and-Mayonnaise Glazed Asparagus in Food & Wine. I was having a losing streak with bland, oily zucchini on the grill—so taking a cue from that recipe, I dunked zucchini coins in a mayo marinade and grilled them until bronzed. They were by far the best vegetables I’d ever grilled," she told me. Not only does mayo get prevent sticking, but "because mayo is an emulsion of oil and egg yolks, it adheres well to vegetables and creates a gorgeous blistered crust and rich flavor that you just can’t get from oil alone."
Add up everyone's advice and the takeaway is clear: What makes a good grilled vegetable is subjective. Try an experiment, like Joshua did—say with a few bread slices or zucchini boats or onion wheels—and see if you like them better with the grates oiled or not, and with the ingredients oiled before or after. Try a mayo marinade, customized with your favorite flavors, like Dijon mustard or Sriracha or fish sauce. Then, use these results to form your own strong opinion about grilled vegetables. And, of course, report back and let me know what it is.
This post contains products that are independently selected by our editors and writers, and Food52 may earn an affiliate commission. Do you oil vegetables before or after you grill them? Why? Get fired up in the comment section.
Any Night Grilling is your guide to becoming a charcoal champion (or getting in your grill-pan groove), any night of the week. With over 60 ways to fire up dinner—no long marinades or low-and-slow cook times in sight—this book is your go-to for freshly grilled meals in a flash.
Emma is a writer and recipe developer at Food52. Before this, she worked a lot of odd jobs, all at the same time. Think: stir-frying noodles "on the fly," baking dozens of pastries at 3 a.m., reviewing restaurants, and writing articles about everything from how to use leftover mashed potatoes to the history of pies in North Carolina. Now she lives in Maplewood, New Jersey with her husband and their cat, Butter. Stay tuned every Tuesday for Emma's cooking column, Big Little Recipes, all about big flavor and little ingredient lists. And see what she's up to on Instagram and Twitter at @emmalaperruque.