Energy is used throughout the U.S. food system. From the manufacture and application of agricultural inputs, such as fertilizers and feed, to building and powering the machines that turn wheat into bread and hogs into bacon, to making and running the toaster and frying pan used by the consumer at home or by the short order cook at the diner, energy fuels the U.S. food system.

An ERS analysis of food system energy use indicates that, while total per capita U.S. energy consumption fell by 1 percent between 2002 and 2007, food-related per capita energy use grew nearly 8 percent as the food industry relied on more energy-intensive technologies to produce more food per capita for more people.

Examining U.S. food system energy use

Using a framework known as input-output material flow analysis, ERS researchers traced energy use by the U.S. food system, measuring the direct energy used to power machinery, as well as the “embodied” energy used in building and distributing the machinery. Thus, the fuel used to manufacture tractors and to run them on farms was measured. Likewise, the ERS analysis accounts for the electricity to power the microwave oven in the home and the energy used to build and distribute the appliance to consumers.

The input-output analysis framework also includes the energy embodied in other inputs to the food production and marketing system, such as fertilizers, shipping crates, and packaging materials. Energy flow analysis captures both direct and indirect energy flows of the entire food chain, from growing and processing the food, to grinding the plate scraps in a garbage disposal.

The two most recent U.S. benchmark input-output accounts from the U.S. Department of Commerce’s Bureau of Economic Analysis (BEA) show that energy use by the U.S. food system grew at more than six times the rate of increase in total domestic energy use between 1997 and 2002. A projection of food-related energy use based on total U.S. energy consumption and food expenditures in 2007 and on the benchmark 2002 input-output accounts suggests that the U.S. food system accounted for 15.7 percent of total U.S. energy consumption in 2007, up from 14.4 percent in 2002.

Three factors drive increased energy use

For greater accuracy, ERS researchers used the survey-based benchmark input-output accounts from 1997 and 2002, rather than the 2007 projections, to discern the largest or fastest growing users of energy and the factors that sparked increased food-related energy use. Between 1997 and 2002, energy use in the U.S. food system grew from 11.5 quadrillion Btu (qBtu) to 14.1 qBtu (British thermal unit—a standard measure of thermal (heat) energy). This 2.6-qBtu increase accounted for over 80 percent of the rise in total U.S. energy use between 1997 and 2002.

Three factors were responsible for the jump in food-related energy use:

Population growth accounted for 25 percent of the higher food-related energy use in 2002 versus 1997. The U.S. population grew by more than 14 million (5.1 percent) over the 5-year period. More mouths to feed means increased production of food and food-related items, ranging from fertilizers to frying pans, pushing energy used by the food system up by 0.64 qBtu.

Higher food expenditures also boosted U.S. food system energy use by 25 percent. The amount of food marketed to U.S. consumers, measured in real (adjusted for inflation) dollars, increased 6.6 percent per capita between 1997 and 2002, according to BEA data.  In 2002, the mix of commodities marketed to U.S. consumers included a greater proportion (in real dollar terms) of foods that used less energy, such as fresh produce and fish, and a smaller proportion of more energy-intensive commodities, like processed fruit and vegetables, pork, and beef.  This changing mix, however, was accompanied by the substantial increase in food marketed per capita to U.S. consumers, resulting in a net increase in total food-system energy use of 0.65 qBtu.

The use of more energy-intensive technologies accounted for about half of the 1997-2002 food-related energy increase. Businesses and households look for efficiency gains, so the relative costs and substitutability of energy and labor are major determinants of the amount of energy used by the U.S. food system. Between 1997 and 2002, businesses faced increasing labor costs, while energy prices were lower and far less volatile than they have been since 2002. A shift from human labor to energy-using equipment occurred for all food and food-related commodity groups, except pork.

The egg industry illustrates the long-term trend of substituting energy-intensive technology for labor. High-technology, energy-intensive hen houses, and more use of liquid, frozen, and dried egg products (instead of whole eggs) increased energy use per egg by 40 percent in 1997-2002. Processed egg products are widely used by the foodservice industry and by processors as ingredients in other foods, such as mayonnaise and baked goods.

The story is much the same in kitchens across the country. Consumers are relying on blenders and food processors instead of knives and chopping blocks, and self-cleaning ovens have replaced EASY-OFF and elbow grease. Modern appliances, while sometimes more energy efficient, still require energy to manufacture and operate. ERS estimates that food-related home energy use increased by 3.9 percent per meal between 1997 and 2002.

Households: biggest energy users

In 2002, U.S. households used 3.94 qBtu of energy on food-related tasks—28 percent of total food system energy use. ERS research indicates that a typical U.S. household would have used about a half million more Btu per person in 2002 than in 1997 for the same foods.

More households adopted labor-saving technologies to save time and effort on food preparation and cleanup. In 1985, 18 to 64 year olds spent an estimated average of 49 minutes on cooking and cleanup per day. Bureau of Labor Statistics’ data indicate average cooking and cleanup times per household fell to 31 minutes per day in 2008.

The share of U.S. households with energy-using dishwashers, microwave ovens, and self-cleaning ovens increased substantially between 1997 and 2005, providing more evidence of an energy/labor tradeoff. At the same time, the percentage of U.S. households with two or more refrigerators increased from 15.2 percent in 1997 to 22.1 percent in 2005; there were 9.2 million more households with two or more refrigerators in 2005 than in 1997.