A Brief History of Oven Temperature—and Why It’s Not as Exact as You Think

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Aug. 8 2012 3:30 AM

Ignore Your Oven Dial

You can’t control the temperature of your oven very well, so stop worrying about it.

Oven dial at 350 F.
Your oven may say 350 degress, but can it be trusted?

Noa Younse/iStockphoto.

“Preheat oven to 350 degrees.” I hate this phrase. First, as George Carlin pointed out, it’s linguistically absurd—you don’t preheat an oven, you heat it. More importantly, however, it gives you a false sense of how much control you have over your oven. It’s also plain terrible advice, in many cases. Join me, if you will, on a brief history of oven temperatures.

For most of human history, bakers had very little control over the heat of their ovens and hearths, and they knew it. The earliest ovens were giant pits filled with hot coals or burning wood, and though technology improved over the millennia—brick or ceramic chambers eventually came into fashion—the basic concept remained the same through the beginning of the 20th century. As a result, estimating oven temperature was more art than science. Bread bakers, for example, dusted a little flour on the bottom of the oven after heating it. If the flour turned black without catching fire, the oven was hot enough. Others placed a strip of paper in the oven and timed how long it took for the paper to turn brown. The most common method seems to have been holding one’s arm in the oven until it became intolerable. (If you could count to thirty, the oven wasn’t hot enough for bread.)

Recognizing these technological limitations, recipe writers in the 19th century described only three temperatures: “slow,” for thin and delicate foods with low water content, “moderate,” for muffins and cookies, and “hot,” for crusty breads. Meats and vegetables usually got the slow or moderate treatment. (There was some variation in terms—you might see “high moderate” or other nuanced alternatives to the big three—but recipes almost never stated degrees.) By the 1920s, new models of gas and electric ovens gave cooks slightly more control over their hot boxes, but the dials still typically only offered low, medium, and high settings. It was primitive, sure, but, somehow, bread still got baked.

Around the end of World War II, manufacturers started including temperatures on their dials, featuring hash marks indicating 10- or 25-degree increments. It’s not particularly surprising that this development came when it did. The war victory, driven largely by scientific and industrial advancement, convinced Americans that they could control every minute aspect of their lives. British manufacturers did something similar, only slightly less specific: Their postwar oven dials were notched with 10 “gas marks.” Baking recipes of the era instructed cooks to bake for 30 minutes at “gas mark six” or “gas mark seven.” As time passed, oven thermostats became even more precise. Modern, electronic ovens often let you punch in your preferred temperature in 5-degree increments.

You’d be forgiven for thinking that 350 on the dial means 350 in the oven. You’d be wrong, though. When you set an oven to 350 degrees, there isn’t a single spot inside of it that stays at 350 degrees for the duration of a bake session. The modern gas or electric oven has an automatic thermostat that, by design, lets the temperature drop a predetermined number of degrees below your chosen temperature before switching the heat on. The heat then surges the oven well past the desired temperature before shutting off again. A 350-degree residential oven is designed to stay between around 330 and 370 degrees—and that’s if it’s well-calibrated, which few ovens are. And that’s just at the location of the internal thermostat—the rest of the oven is a different story. Every oven has hot and cool spots so difficult to predict that oven design has become something of a mystical pursuit.

Most of the conventional tips to help you better understand your oven are a waste of time. Television chefs urge viewers to buy an oven thermometer to make sure their hot box isn’t lying to them, but, unless your thermostat is consistently and significantly off in the same direction, the variability in temperature throughout the chamber makes this trick pretty useless. Obsessives have their ovens professionally recalibrated annually, but this does nothing to address the temporal and spatial fluctuations of heat that are features of how ovens work.

The old, vague system is much better than the myth that you can micromanage your oven temperature down to the degree. An oven is an insulated box with a fire in it—there’s only so much control you can have over that setup, and we might as well be honest about it. Plus, once we recognize that oven temperature is a major and largely uncontrollable variable in how our precious baked goods turn out, we might relax a little about the other aspects of the process. What’s the point of measuring flour down to a hundredth of an ounce, or buying a plunger measuring cup to ensure that you don’t leave a few drops of honey clinging to the side of a container, when you’re just throwing your food into a black box of unknown temperature?

The 350-degree instruction is often just a default, anyway. Around the time that manufacturers put temperature dials on ovens, cookbooks had to convert their old terminology into degrees. A “moderate” oven became 350 degrees, and few writers bothered to test if 350 was really better for an individual recipe than, say 360 or 380.

Mark Bittman, New York Times food columnist and author of How To Cook Everything (the Joy of Cooking for our generation) agrees that “oven temperatures are a convention.”

“I tend to think of oven temperatures in maybe four ranges,” Bittman says. “[R]eally low, under 275 degrees; moderate, between 275 and 350; high, over 350 but under, say 425; and maximum. But I don’t think about those numbers ... I just think ‘what am I trying to do here? Blast this stuff or treat it gently, or something in between?’ ”

Food manufacturers take a more technical approach, but even the exhaustively tested instructions on a box of cake mix are usually wrong.

“When you’re developing cooking instructions for a major food manufacturer, you have two different groups looking over your shoulder,” says Brian Smith of Booth Smith Food Technology, a consultancy that helps food companies design and bring new products to market. “The technical people want the product to be as good as it can be, but the marketing people don’t want customers calling them up complaining about burned cake.”

And the marketing people almost always win. The ideal baking temperature as determined by an industrial test kitchen is often significantly higher than what it says on the box. But food-makers assume that you’re not vigilant enough to pull your cake, cookies, or brownies out of the oven before they’re toast. You’re often better off setting the oven 50 or more degrees above the recommended temperature, and watching your food like a hawk.

Or you could give up on the numbers, and follow Bittman’s advice: “Cooks should get used to the visual and olfactory (and even aural) cues that food gives off while it’s baking or roasting.” And if you’re not confident enough to trust your eyes, nose, and ears, use a thermometer—not the kind that sits inside your oven, but the kind you stick in the food as it’s cooking. ”The instant-read thermometer, used frequently, solves most issues,” says Bittman.

Brian Palmer is Slate's chief explainer. He also writes How and Why and Ecologic for the Washington Post. Email him at explainerbrian@gmail.com. Follow him on Twitter.