What's the greenest way to cook up classic holiday fare?

Illuminating answers to environmental questions.
Dec. 7 2010 6:56 AM

A Merry, Planet-Friendly Cook-Off

What's the greenest way to cook up classic holiday fare?

Microwave.
Microwaving your foods is more energy-efficient than roasting them in a conventional oven

I'm planning our family's holiday feast. I know the foods I want to serve but am wondering how to cook them in the eco-friendliest way. Should I roast or fry the turkey? Are baked, microwaved, or boiled potatoes easier on the earth?

With the exception of transportation, no sector takes more heat for greenhouse-gas emissions than the food industry. Rajendra Pachauri, Nobel laureate and president of the Intergovernmental Panel on Climate Change, has urged people to eliminate meat from their diet once a week—a shift he says would eliminate 170 kilograms of carbon dioxide emissions per person every year. And the locavore movement is keen to remind us that our food travels about 1,500 miles on average from field to table.

But you might want to pause before blaming climate change on tomato-hauling tractors and methane-belching cattle: Your kitchen is the single greatest contributor to carbon dioxide emissions in the food chain. By some estimates, cooking accounts for 37 percent of the greenhouse gases generated in a potato's life cycle, almost twice as much as shipping them to market.

So how can you reduce your kitchen's environmental footprint without becoming a raw foodist? Cutting your foods into smaller pieces increases the ratio of surface area to volume, allowing them to cook more quickly. Direct cooking methods using high heat, like stir-frying, are better than baking and roasting, which depend on radiation and convection rather than conduction. Heating up large amounts of liquids, especially water, which has a high specific heat, is usually an inefficient way to cook.

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Let's see how these principles apply to the humble potato. Baking a single tuber in the oven is the least energy-efficient cooking method, by far. (Baking is so energy intensive that the federal government has so far refused to bestow the Energy Star label on any oven.) Most recipes call for about an hour in a 350-degree oven. Using an electric oven, this method would require two kilowatt-hours of electricity, enough to run a 60-inch television for more than eight hours. (Gas ovens are somewhat more efficient than electric ovens on average, but individual models' efficiencies vary widely.)

You could save some serious carbon by tossing your potato in the microwave, even if the result is a leathery, limp facsimile of the oven-baked equivalent. Nuking your tater on high for eight minutes uses only 0.19 kilowatt-hours of electricity—just 10 percent of the oven's output.

Boiling potatoes requires trickier calculations. Covering the pot and using as little water as possible will reduce your energy consumption. Choosing the right pot also makes a big difference: on an 8-inch burner, a 6-inch pot is 40 percent less efficient than an 8-inch pot. Warped cookware that doesn't have good contact with the burner can double energy use.

Once you get the water boiling, lower the heat as much as you can without losing the boil. Since water can't get hotter than 212 degrees under most conditions, a high flame won't cook your taters faster. A 6-inch electric burner running on high consumes around 1.2 kilowatts. If it takes 10 minutes to get the water boiling, and you cook the potatoes for 30 minutes on high, you'd use 0.8 kilowatt-hours. You could cut that down by 30 percent or 40 percent if you dialed back the burner a bit, which, in terms of energy use, would put boiling between microwaving and baking.

A green-obsessed gourmet's only hope of avoiding the microwaved potato is turning to the hash brown. Grandma might blanch at the idea of serving diner fare at the holiday table, but Mother Earth will thank you. By shredding a potato and taking the water out of the equation, the cooking time drops enough to beat the microwave's 0.19 kilowatt-hours.

Now, about that bird. Frying a whole turkey has become popular in recent years, but how green is it? As with stovetop-energy estimates, there is a lot of guesswork involved. Propane cookers vary widely in efficiency, and the volume of oil also affects total consumption. But, generally speaking, it takes about 20 minutes to preheat the oil and another 35 minutes to fry a 13-pound bird. Running a propane tank for an hour on medium-high heat releases around 25 pounds of carbon dioxide.

Roasting a similar-size bird—that is, putting it in an electric oven at 350 degrees for 3½ hours—would use about six kilowatt-hours. To generate this much electricity, your average power plant emits about 7.8 pounds of carbon dioxide, making the old-school oven-roasted turkey the clear winner.

During this stressful holiday season it's helpful to remember, however, that these are fairly minor differences. To compensate for the fried turkey's 17 extra pounds of carbon dioxide, you'd need to drive just 19 fewer miles. If you really want to scrimp on CO2, just tell your in-laws you're staying home this Christmas for the sake of the earth.

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Brian Palmer writes about science, medicine, and the environment for Slate and Earthwire. Email him at explainerbrian@gmail.com. Follow him on Twitter.

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