The United States food system uses about 4,300 terawatt-hours (TWh) annually, which represents about 15 percent of total primary energy consumption (it was estimated to be 14.4% in 2002).
So how, specifically, is energy consumed in the food system? While its slice of the overall energy pie may seem relatively low, the modern American food system is figuratively awash in fossil fuels. On average, roughly 12 calories of (mostly fossil fuel) energy go into producing just one calorie of the food that we consume. The use of fossil fuels in every phase of the food system—from fertilization, treatment, and harvesting to manufacturing, packaging, distribution, and preparation—has utterly transformed what we eat, how we eat, where we eat, and how our food is grown. Arguably, our bodies have gone through as much transformation as a result of the industrialization of agriculture as the food system itself.
Refrigeration—critical to the long-distance supply line of many foods—is one of the biggest users of energy in the food system (approximately 15 percent, if you include refrigerated trucks, household refrigeration, and retail), employing electricity in the great majority of cases.
While agriculture is the basis of the food system, it accounts for only about 13 percent of food system energy. In industrial farming, the single largest energy input is in the form of fertilizer, which relies on a process that transforms fossil fuels (usually natural gas) into ammonia.
Farm machines such as tractors, harvesters, and combines burn diesel fuel, while pesticides and herbicides are typically made from petrochemicals.
Processing of food is also highly energy intensive (17 percent of food system energy), with natural gas and electricity being used for cooking, baking, grinding, slicing, blending, and other activities.
Packaging accounts for five percent of food system energy, via the production of plastics (mostly from fossil fuel feedstocks, though some bioplastics are entering the stream) and cardboard. The latter is often recycled, but much end-use packaging is simply discarded to landfills.
Transport of inputs to farms, and outputs from the farm to table, accounts for about three percent of food system energy; as noted in the transportation sector description, the great majority of energy used for these purposes is in the form of oil.
Within the overall food system, energy is embodied in farming, transport, and processing machinery, as well as packaging. However, food itself represents embodied energy: As stated earlier, about 12 calories of energy are currently required to produce, process, and deliver each calorie of food (on average) within the U.S. food system. However, some foods are far more energy-intensive than others: whole grains, fruits, and vegetables embody less energy, while meat (especially beef) and highly processed snack foods embody much more.
Example: A Bowl of Cornflakes
Cornflakes are part of many Americans’ breakfast. But how do they get to the table, and what energy is needed to make that happen?
The story of a bowl of cornflakes begins on a farm—say, in Iowa—which grew corn using diesel fuel (derived from oil) to power machinery for plowing, seeding, harvesting, and production. Oil-powered machines were also used for applying nitrogen fertilizer and herbicides, and even earlier for mining, transporting, and processing phosphorus and potassium fertilizers. After harvest, the corn was trucked (using oil) to a grain elevator, where it was dried (natural gas); then it was transported by rail (oil) to Michigan for processing.
After processing, the cornflakes were packaged in a plastic bags (oil) and cardboard boxes. The boxes were made from wood pulp originating in Georgia (oil for harvesting and transport, gas for processing heat), and the graphics on the box were printed (the presses run on electricity) using petroleum-based inks.
The boxes of cornflakes were trucked (oil) to a warehouse (most operations including lighting, cooling, and pallet trucks are electric). From there the cornflakes were trucked (oil) to the store where they were purchased. They were then transported home—most likely by car (more oil).