How 'Green' Is Home Cooking? | Science News


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Food for Thought

Janet Raloff
Food for Thought

How 'Green' Is Home Cooking?

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Which is better for the environment: a meal cooked from scratch at home or a packaged frozen or freeze-dried meal cooked up in distant industrial kitchens and trucked to supermarkets? Most consumers would guess the former, notes environmental engineer Ulf Sonesson. Even many food scientists would vote for home cooking as the greener option, he says.

However, those guesses probably wouldn't be taking into account economies of scale in food companies' mass preparation of meals, says Sonesson.

Indeed, when he and his team at the Swedish Institute for Food and Biotechnology made calculations including such efficiencies, they found no big difference between the environmental footprints of home-cooked versus ready-to-eat fare. Each means of putting food on the table has environmental advantages and disadvantages that, in the end, "even each other out," the researchers concluded.

A major reason the resource costs of the two different types of meals are so similar, overall, is that cooking itself contributes comparatively little to environmental costs of a meal. Most impacts instead occur around the farm or in the marketplace—upstream of food preparation—and contribute comparably to meals, regardless of where they're cooked.

That's potentially good news for the environment, Sonesson says, since in Sweden, as in the United States, there is growing reliance on meals that are partially cooked or ready-to-eat, needing little more than last-minute heating.

Cooking's hidden costs

The Swedish scientists focused their analyses on the farm-to-fork, or life-cycle, costs of preparing a meal of meatballs, potatoes, bread, carrots, and milk. They chose this combo because it's popular in their country and because it can be purchased as a frozen, ready-to-eat meal (minus the bread and milk) or as separate, semi-prepared foods (such as dried mashed potatoes and refrigerated meatballs). The former meal needs only to be microwaved prior to eating. The latter requires frying the meatballs on a stovetop and adding water to reconstitute the potatoes before heating. To complete both of these meals, store-bought milk and bread were added.

The researchers compared the life-cycle costs of the prepared and semi-prepared meals with the cost of a homemade alternative. For this version of the meal, all foods—including the bread—were made from scratch. Carrots were peeled and eaten raw, meatballs were rolled from ground meat, and the milk came from the supermarket.

In each food-preparation scenario, the researchers assumed that all portions or ingredients of the meal would be purchased on the day it would be eaten.

In the June Ambio, Sonesson's group reports that agriculture accounted for roughly half of the resource costs associated with any of the meals, owing mostly to the energy associated with producing and applying fertilizer and with the use of diesel-powered gear, such as tractors. For the two meals produced commercially, packaging made up another 10 percent of the environmental costs. Energy costs at food retailers—refrigeration of individual ingredients, for instance—proved highest for the home-cooked meal, accounting for about 20 percent of the energy associated with it. The retailer-energy cost of semi-prepared and ready-to-eat meals was slightly smaller—although the amounts of energy used outside the home to prepare these meals were slightly higher—than that for the homemade meal.

That said, the energy expended to bring each meal to the table varied only slightly—from about 9 megajoules per meal for the home-cooked food, to a little over 10 Mj for the full complement of foods served in the largely ready-to-eat meal. Each megajoule is equivalent to about the energy needed to keep three 100-watt light bulbs burning for 1 hour.

Emissions of greenhouse gases, such as carbon dioxide or methane, were somewhat higher for the home-cooked meal. One reason, Sonesson explains, is because much potentially wasted energy in commercial preparation of foods was recaptured—such as by the incineration of food scraps. Production of smog-inducing gases proved highest for the semi-prepared meal, largely because it required the most plastic for packaging the various components.

Emissions of nitrogen oxides, a component of smog and acid rain, were highest overall for home-cooked meals, Sonesson's group found. One major reason: potato peels.

Industrial processing discards about one-third less potato as scrap during peeling. Not only does this mean that fewer spuds need to be grown to supply an equivalent amount of potato for an industrially produced meal, but also that less peel will be discarded in a landfill, where it decomposes into the polluting gases. The extra spuds needed to make up for higher peeling losses in home kitchens also led to proportionately more fertilizer use and thus farm runoff of fertilizers into waterways.

The cost of waste

In a second paper published in Ambio, Sonesson's team investigated additional environmental costs associated with food production. Through surveys of some 270 households, the researchers learned that most grocery shopping is done by car. Only one-quarter of household trips to stores were on foot, usually to a local or convenience store, not the supermarket. Most of the Swedes surveyed said that they shop for food every 1 to 3 days, typically coming home with only a bag or two of groceries.

Frequent shopping by car aggravates air pollution and elevates fossil-fuel consumption. On the other hand, it suggests that people are buying only as much food as they need. Buying in bulk, in contrast, could cause people to waste food. To probe that idea, the researchers scoured data from 35 households to evaluate how much of a family's food typically went to waste.

The families reported discarding roughly twice as much dairy food as they ate. Of that wastage, about 80 percent was never used in a meal and 20 percent was prepared but eventually discarded as leftovers. Produce losses also proved high. An amount equivalent to nearly 50 percent of the fruits and vegetables eaten was thrown away, apparently because it went bad prior to being incorporated into a meal. On the other extreme, pasta, rice, potatoes, and other staples with a long shelf life were seldom pitched out uneaten, according to food diaries kept by the participating families.

Sonesson and his colleagues observe that few studies have addressed why people discard food. Is it spoiled? Has it merely exceeded its "sell by" date? Or do people get bored with certain items?

Understanding the factors prompting food waste is important, Sonesson argues, because substantial energy and environmental resources go into food production. In Sweden, for instance, agriculture consumes some 20 percent of the nation's energy. With on-farm costs of this industry so large, Sonesson says, finding ways to limit demand for excess production—food that will never be consumed—could provide substantial benefits for both the nation's economy and environment.


Ulf Sonesson

Swedish Institute for Food and Biotechnology (SIK)

P.O Box 5401

S-402 29 Göteborg

Further Reading

Gorman, J. 2002. The short and long of the food transport story. Science News Online (Nov. 23). Available at [Go to].

Raloff, J. 2004. Limiting dead zones. Science News 165(June 12):378-380. Available at [Go to].

______. 2003. Local foods could make for greener grocers. Science News Online (Aug. 2). Available at [Go to].

______. 2003. Global food trends. Science News Online (May 31). Available at [Go to].

______. 2002. Home cooking on the wane. Science News Online (Dec. 7). Available at [Go to].

______. 2002. Finned pollution is one cost of our exotic tastes. Science News Online (Nov. 16). Available at [Go to].

______. 2000. Toxic runoff from plastic mulch. Science News (Sept. 30):221. Available to subscribers at [Go to].

______. 1998. How farm-fed seafood can deplete wild fisheries. Science News Online (Nov. 7). Available at [Go to].

______. 1997. The environment upstream of our supermarket. Science News Online (March 29). Available at [Go to].

______. 1996. A valuation of our convenience economy. Science News Online (Oct. 26). Available at [Go to].

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