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Wasted Food, Wasted Energy: The Embedded Energy in Food Waste in the United States

Wasted Food, Wasted Energy: The Embedded Energy in Food Waste in the United States Environ. Sci. Technol. 2010, 44, 6464–6469 system are available, and, despite the enormous energy Wasted Food, Wasted Energy: The investment we make in food production, the USDA reports that about 27% of available food was wasted in 1995 (8). Embedded Energy in Food Waste in This estimate does not include food wasted on the farm, in fisheries, and during processing and relies on outdated the United States food consumption and waste data, some of which is from the 1970s. Because of economic and population growth, AMANDA D. CU ELLAR the total amount of food production and consumption Center for International Energy and Environmental Policy, has grown since the latest food loss study for 1995 (9), and The University of Texas at Austin the portion of income Americans spend on food has dropped (10, 11). Consequently we expect the current MICHAEL E. WEBBER* amount of food wasted to be higher both relatively and Mechanical Engineering, Center for International Energy and absolutely as compared to the USDA’s 1995 estimates. Since Environmental Policy, The University of Texas at Austin food production requires about one-tenth of the energy consumed annually in the U.S., the energy embedded in wasted food might also correspond to a significant portion Received January 28, 2010. Revised manuscript received of energy consumption in the U.S. and represents an June 15, 2010. Accepted July 2, 2010. opportunity for avoided energy consumption. Because of the desire to reduce greenhouse gas emissions, concerns about fossil fuel availability, and the expected This work estimates the energy embedded in wasted food increase in population (12), the reliance of food on fossil annually in the United States. We calculated the energy intensity energy sources has become more scrutinized. In order to better understand the relationship between food and energy, of food production from agriculture, transportation, processing, a current estimate for the energy embedded in food produc- food sales, storage, and preparation for 2007 as 8080 ( 760 tion is needed as well as a calculation of the energy that is trillion BTU. In 1995 approximately 27% of edible food was wasted. lost in wasted food. No such study using current data has Synthesizing these food loss figures with our estimate of been identified in the literature. Consequently this work seeks energy consumption for different food categories and food to fill that knowledge void and provide important data that production steps, while normalizing for different production will quantify both the energy required to produce food in the volumes, shows that 2030 ( 160 trillion BTU of energy were U.S. in 2007 and the energy embedded in wasted food. embedded in wasted food in 2007. The energy embedded in This work will calculate the amount of energy used to wasted food represents approximately 2% of annual energy produce food from agriculture, through transportation, consumption in the United States, which is substantial when processing, retailing, and finally for preparation and con- compared to other energy conservation and production proposals. sumption. These data will then be combined with food loss To improve this analysis, nationwide estimates of food waste factors from the USDA (8) to calculate the energy lost in wasted food. Because the data available on food production and an updated estimate for the energy required to produce food and food waste are from different years, all data will be for U.S. consumption would be valuable. considered as a percentage of annual energy production for that year and extrapolated to obtain an estimated 2007 energy Introduction value. Energy for Domestically Consumed Food. First, we Recent food shortages, blamed in part on the growth of the calculated the energy required to produce food. Despite biofuels industry (1, 2), have created a new awareness of the various literature sources that estimate the energy required relationship between food and energy. Food is not only a for U.S. food production (5, 7, 13, 14), we recalculated this form of energy but also a consumer of fossil energy in its value for 2007 to generate an estimate organized in a way production, transportation, and preparation. Historically this that is compatible with the available food waste data. For has been a positive relationship: the last 50 years have seen our estimate of the energy required to produce food increased agricultural productivity thanks to the adoption of consumed in the U.S. we compiled data from various sources new technologies and inputs (3), which are largely based on including government reports and scientific literature. Data fossil fuels. The increase in the energy intensity of agriculture for the energy consumed in food production is mostly from has brought with it unprecedented yields with minimal the year 2002, whereas the available data on food loss is from human labor. Productivity improvements have been achieved 1995 and food quantities are given for 2004. In order to through a variety of means, including mechanization of the minimize error, the energy values for food production were agriculture sector, improved fertilizers, more resilient crops, determined for 2002 and then scaled to estimate 2007 values. and the development of pesticides (4), all of which rely on A summary of the results is shown in Table 1, along with the fossil fuels. year of the data source and citation. The Supporting Prior estimates for the amount of energy consumed by Information (SI) contains details of our methodology. the United States (U.S.) to produce food range from 10.5% While we expect that all values listed in Table 1 have (5) to 14.5% (6) of annual energy consumption. The newest significant uncertainty, none of the published data include estimate, released in March of 2010, estimates that 15.7% error estimates. A range of error is not given in Table 1 of energy consumption in 2007 was used to produce food unless we have multiple estimates for a single value in (7). Despite the significance of the food system as an energy Table 1 in which case we use the standard deviations of consumer, few estimates for the energy intensity of the the multiple estimates to approximate the error. For other listings, in Table 1 when we have a single estimate (that * Corresponding author e-mail: webber@mail.utexas.edu. Current is, for all categories except transportation and nitrogenous address: Department of Mechanical Engineering, 1 University Station C2200, The University of Texas at Austin, Austin, TX, 78712. fertilizers included in agricultural chemicals, fuel, and 6464 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 16, 2010 10.1021/es100310d  2010 American Chemical Society Published on Web 07/21/2010 a TABLE 1. Food Production in 2002 Required at Least 7790 ± 732 Trillion BTU in the U.S. food production steps [index ) i] energy [trillion BTU] year source ag. chemicals, fuel, electricity 1160 ( 69 2002 (adjusted) see the SI fisheries 18 2000/2002 (15–17) aquaculture, domestic 8.8 2002 (adjusted) (18, 19) aquaculture, imported 55.8 2002 (adjusted) (18, 20) agriculture total [1] 1240 ( 70 transportation, all modes 1650 ( 520 2002 (adjusted) (13, 18, 21–25) transportation total [2] 1650 ( 520 food processing 1120 2002 (18) processing total [3] 1120 ( 220 food services and sales 1530 2003 (26) packaging 684 2002 (adjusted) (5, 18) residential energy consumption 1570 2001 (5, 18, 27) food handling total [4] 3780 ( 460 total 7790 ( 730 The food handling step was the biggest contributor to the total. The index “i” is used as an index for the four different food production steps for the calculations using eqs 1 through 4 and equation S11 (see above and the SI for more information). electricity, see the SI for details) we use a 20% uncertainty also use a more complex method for scaling their food because it is the average of the error estimates that we energy estimates to different years, which does not assume were able to calculate for nitrogenous fertilizers (8% error) linear energy growth in the food system in line with total and transportation (32% error). Ultimately, the 20% error energy use in the U.S. bars we use are arbitrary, since they rely on two varying The energy required to dispose of food waste was not estimates of error for nitrogenous fertilizer production and included in this study. Food scraps made up 12.4% of total food transportation. We expect our energy estimate to have municipal solid waste generated in 2006 (28), but a value some range of error because of the assumptions and for the energy required for municipal solid waste disposal estimates we make throughout our analysis. Nonetheless, was not found in the literature. Compared to the estimates we rely on methodologies published in the scientific from the Heller et al., Pimentel et al., and Canning et al. literature and data sets from the U.S. government, which publications, the energy estimate presented here is lower we consider reliable sources. Therefore we use the 20% but within 25% of Heller’s work. Consequently, the energy error bars to not overstate the accuracy of our estimate estimate presented in Table 1 can be considered a lower but also to not undermine the validity of our work in bound estimate of the energy required for food production, estimating the energy required to produce the food consumption, and disposal. consumed in the U.S. Using this method for estimating Energy Embedded in Wasted Food. To calculate the error for individual values we calculate the total uncertainty energy embedded in wasted food we use 1995 food loss data in the energy consumption in 2002 to be (730 trillion BTU provided by the USDA for ten food categories, shown in Table after propagating the calculated and 20% error values 2. These data show that grain products, dairy products, fresh throughout all calculations. [To estimate total uncertainty, vegetables, fresh fruit, and fats and oils are, proportionally, 2 1/2 we used the following relationship: U ) (∑u ) , where the most wasted foods. tot i U is the total uncertainty and u is the uncertainty for The USDA report calculates food loss by retail and food tot i each of the steps listed in Table 1.] The energy estimate service establishments and by consumers. As the authors for food production scaled to 2007 energy values is 8080 of the USDA report note, there are significant food losses ( 760 trillion BTU. In 2002 and 2007 the total energy from other components of the food processing chain that consumption for the U.S. for all sectors was 97,900 trillion are not accounted for. These include losses on the farm, BTU and 101,600 trillion BTU, respectively (18). These from fishing, and during processing. Fishing waste could values were used to scale the energy for food from 2002 be a significant contributor to overall food waste; it is to 2007 assuming linear increases in energy consumption estimated that worldwide approximately 23% of fish for the U.S. and for food production. landings are bycatch, which are thrown back into the ocean, Our estimate for the energy required to produce the usually already dead or dying, instead of being sold and food consumed in the U.S. amounts to approximately 8% consumed (29). The 1997/95 USDA report also makes use of the energy consumed annually for all uses. Heller and of food waste factors from previous reports, some from Keoleian calculated the energy consumed to produce food the 1970s. The USDA applied food loss factors to food throughout its lifecycle for the late 1990s as 10,200 trillion availability data for 1995 to arrive at the percentage results BTU (5), constituting 10.5% of annual energy consumption. shown in Table 2 (5). The methodology used as well as the Pimentel et al. report in 2003 that 14.5% of the U.S. annual age of the food loss estimate implies a large margin of energy consumption is used to produce food; the year for error in these data both for 1995 and for the current the Pimentel estimate is not clear (6). In a 2010 report analysis. We expect that current food loss in the U.S. is Canning et al. found that food production required 15.7% greater (absolutely) than the amount estimated in the 1995 of 2007 energy consumption in the U.S. The Canning USDA work, but assume, for our calculations, that the estimate includes energy estimates for the same steps and relative food waste percentages are the same in 2007 as categories of the food system as we do but draws a larger for 1995. It is possible because of economic growth and boundary around the food system than our study does. the declining price of food as a portion of discretionary For example, Canning’s report includes several energy income that relative food waste percentages actually inputs that we did not include, such as the energy used increased over that time span. Due to unaccounted food by consumers to purchase food (fuel for driving to food losses and the potential for increased waste due to stores), and the energy required to produce modes of economic conditions we expect the results in the present transportation used in food procurement. Canning et al. analysis to represent a lower bound. VOL. 44, NO. 16, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 6465 E ) E (1) tot ∑ i TABLE 2. The USDA Estimates That 27% of Edible Food Was Wasted in 1995 with Fresh Foods (Fruit, Vegetables, and Dairy Products) and Fats and Oils Being the Most Wasted Equation 1 states that the energy consumed to produce Food Categories (8) food is equal to the sum of the energy required for each production step (E ), i, shown in Figure S1 and listed in Table edible food 1. For eq 1 the energy intensity (and therefore embedded commodity supply total loss % of total energy in wasted food) also varies by food category. Con- [index ) j] [billion lbs] [billion lbs] [%] (f ) sequently we rewrite eq 1 to account for the differences in grain products [1] 45.6 14.6 32.0 energy intensity between food categories as eq 2 fruit [2] fresh 22.4 7.2 32.0% E ) E (2) processed 25.9 4.2 16.0% tot ∑ ∑ ij i j total fruit 48.3 11.3 23.4% vegetables [3] In eq 2 the total energy for food production is the sum fresh 36.8 11.8 32.0% of the energy required to produce each food category, j (listed processed 26.2 4.2 15.8% total vegetable 63.1 15.9 25.3% in Table 2), at each production step, i. However, values for dairy products [4] E are not available in the literature, and thus they must be ij fluid milk 54.5 17.4 32.0% deduced. Consequently we replace E with the total energy ij other dairy products 21.8 7.0 32.0% required for each production step i and the relative energy total dairy 76.3 24.4 32.0% intensity for food category j and production step i, A ,as ij meat, poultry, and fish [5] shown in eq 3 red meat 30.4 4.9 16.0% poultry 17.1 2.7 16.0% fish and seafood 4.0 0.64 16.0% E ) E A (3) tot ∑ ∑ i ij total meat 51.5 8.2 16.0% i j eggs [6] 7.9 2.5 31.4% dry beans, peas, 2.3 0.36 15.9% When we include the fraction of food lost in each category and lentils [7] (f ) in eq 3 we obtain an estimate for the energy embedded tree nuts and 1.9 0.30 15.9% in wasted food (E ) as shown in eq 4 loss peanuts [8] caloric sweeteners [9] 38.8 11.9 30.5% E ) E A f (4) fats and oils [10] 20.3 6.8 33.4% loss ∑ ∑ i ij j i j total 27.0% 356 96.3 (of total) In eq 4 E and f can be determined by normalizing and a i j The index “j” is used as an index for the ten different scaling values published in the literature, as shown in Tables food categories for the calculations using eqs 2 through 4, 1 and 2. In this section we will develop reasonable estimates S1 through S4, and S8 through S11 (see above and the SI for A , which we will then use to calculate the total energy ij for more information). The term “f ” is used to denote the embedded in wasted food. fraction of the total production for food category “j” that is wasted. We calculate A in three different ways for the different ij production steps. In agriculture some products are far more energy intensive than others. For instance, the production To calculate the energy embedded in wasted food we will of animal products requires energy to grow the animal’s feed calculate the energy required at each of the four food produc- and must account for efficiency losses in the animal when tion steps (shown in Table 1 as i ) 1to i ) 4) to produce food converting feed to edible mass. We use data from Pimentel in the ten categories (shown in Table 2 as j ) 1to j ) 10) and (30, 31) on the amount of energy necessary to produce a kcal then use the food loss percentages (f from Table 2) to calculate of protein energy for subcategories in eight different food the energy embedded in wasted food. First we define the energy categories (grains, fruits, vegetables, meat, dairy, eggs, dry consumed annually for food production (E )ineq1 beans, peas, and lentils, and tree nuts and peanuts), and tot TABLE 3. Energy Required for the Agricultural Production (i = 1) of Food Categories for Different Food Categories Was Calculated Using Relative Intensity Factors and the Mass of Agricultural Products before Processing weighted average energy for food agriculture energy, food category energy intensity annual consumption production relative energy by food category [index ) j] by mass (e¯ ) [kcal/lb] [million tons] [trillion kcal] (E ) intensity (A ) [%] (E ) [trillion BTU] avg,j ij 1j 1j grains [1] 381 73.8 56.2 5.62 71.4 vegetables [2] 310 68.0 42.2 4.22 53.5 fruit [3] 259 41.0 21.2 2.12 26.9 dairy [4] 2220 41.5 184 18.4 234 meat, poultry, fish [5] 7070 43.3 613 61.3 778 eggs [6] 7840 4.88 76.5 7.64 97.1 dry beans, peas, 71.8 48.8 7.01 0.70 8.89 and lentils[7] tree nuts and 85.7 1.5 0.26 0.03 0.33 peanuts [8] caloric sweeteners [9] -- - 00 fats and oils [10] -- - 00 total, 2004 1000 1270 The total energy value for agriculture was scaled from the Table 1 value for 2004, the year of this analysis. 6466 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 16, 2010 TABLE 4. Energy Required for Transportation (i = 2) by Food TABLE 5. Energy Required for the Processing of Food (i =3) Category Was Calculated for 2004 Using the Mass-Based Was Calculated Using Adjusted Mass Based Relative Energy Relative Energy Intensity Values Intensity Values To Account Only for Foods That Undergo Processing before Sale transportation mass of food relative energy energy, by food food processing [million intensity category (E ) 2j mass relative energy energy, by food food category [j] tons] (A ) [trillion BTU] 2j food [million intensity category (E ) 3j grains [1] 28.3 0.11 185 category [j] tons] (A ) [trillion BTU] 3j vegetables [2] 62.2 0.24 407 grains [1] 28.3 0.14 155 fruit [3] 41.2 0.16 270 vegetables [2] 32.5 0.16 178 dairy [4] 41.6 0.16 273 fruit [3] 22.3 0.11 122 meat, poultry, fish [5] 43.3 0.17 284 eggs [6] 4.9 0.02 32.0 dairy [4] 41.6 0.20 229 dry beans, peas, 1.0 0.004 6.5 meat, poultry, fish [5] 43.3 0.21 238 and lentils [7] eggs [6] 4.9 0.02 27 tree nuts and 1.5 0.006 9.8 dry beans, peas, 1.0 0.005 5 peanuts [8] and lentils [7] caloric sweeteners [9] 20.9 0.08 137 tree nuts and 1.5 0.007 8 fats and oils [10] 13.0 0.05 85.4 peanuts [8] total, 2004 258 1690 caloric sweeteners [9] 20.9 0.10 115 fats and oils [10] 13.0 0.06 72 food mass data obtained from the USDA Economic Research total, 2004 209.3 1150 Service (9, 32–35) to calculate the relative energy intensity These values are scaled to represent 2004 energy of each category. For this analysis we were only able to locate consumption. energy intensity values for seventeen food subcategories in the literature. To calculate the energy intensity of the food categories used in this report we first list all of the subcat- TABLE 6. Energy Required for Food Handling (i = 4) by Food egories for which we have data and calculate their energy Category Was Calculated for 2004 Using the Mass Based intensities per mass using the Eshel Martin methodology Relative Energy Intensity Values (detailed in the SI) (36), and then we calculate a weighted average of the energy intensities of the subcategories to relative food handling represent the average energy intensity of the eight food energy energy, by food categories. We used this methodology to mitigate skewing food mass of food intensity category (E ) 4j of the food category energy intensity by an unrepresentative category [j] [million tons] (A ) [trillion BTU] 4j food subcategory and to calculate representative energy grains [1] 28.3 0.11 426 intensity for the entire food category. We use 2004 data for vegetables [2] 62.2 0.24 935 this calculation, thus the results are considered to be for the fruit [3] 41.2 0.16 619 year 2004. The final relative energy intensity values for dairy [4] 41.6 0.16 627 agriculture (A ) are summarized in Table 3. A detailed account 1j meat, poultry, fish [5] 43.3 0.17 652 of our methodology for calculating the relative energy eggs [6] 4.9 0.02 73 intensity of each food category for the agriculture production dry beans, peas, 1.0 0.004 15 step is given in the Supporting Information (SI) that ac- and lentils [7] companies this work. tree nuts and 1.5 0.006 23 The relative energy intensity of each food category for peanuts [8] caloric sweeteners [9] 20.9 0.08 314 agriculture is calculated from the weighted average of the fats and oils [10] 13.0 0.05 196 energy intensity of the food subcategories listed in Table S10 total, 2004 258 3880 and the mass of each food category consumed annually (listed in Table S11). It is important to note that the energy intensity values the amount of food that is produced, since food transporta- from Pimentel used in this study account for the energy used tion is mass-dependent and measured in ton-miles. The mass to produce agricultural inputs to the agriculture sector such of food in Table 4 differs from the masses used to calculate as livestock feed from corn. Therefore, to avoid double- A (shown in Table S10) because it accounts for food in its ij counting, we did not include livestock feed in our analysis finished form (as reported in the USDA Food Availability as it is already accounted for in the energy intensity factors Report for 2004 (9)), rather than in its raw form (for example, used. Also, throughout this study we consider food to be the sugar cane is classified as a vegetable in Table S10 and as a primary product of the agriculture sector. See the SI for more caloric sweetener in Table 4). The calculation of the relative details on our full methodology and considerations. energy intensity for food transportation by food category is Data for the food categories ‘caloric sweeteners’ and ‘fats shown in Table 4. and oils’ are not reported in the Pimentel et al. works; these The A (i ) 3 is for food processing) term used for the 3j omissions are logical since caloric sweeteners and fats and energy consumed in food processing was calculated using oils are made from primary agricultural products, which are mass ratios with the mass of processed fruits and vegetables included in this analysis. We include soy for human used in place of the total mass of these two food categories. consumption (32, 33), corn for processing (35), and sugar In the food availability report the USDA separates fruits and crops (34) into the dry beans and vegetable categories, vegetables that are processed and those that are sold fresh respectively, to account for the missing categories, as a (9). We expect that fruits and vegetables sold fresh have no portion of these crops are used to produce fats, oils, and or minimal processing. Food processing includes such varied sweeteners. operations as grain milling, canning, slaughtering, and all For food transportation we define A (where i ) 2isfor other modes of food preparation. Nearly all food goes through 2j transportation) as the ratio of the mass of a given food some form of processing; consequently we used mass ratios category to the total mass of food production. We assume for A and only included the mass of fruits and vegetables ij that the energy intensity of food transportation depends on that the USDA (9) reports as processed. The calculation of VOL. 44, NO. 16, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 6467 a TABLE 7. Energy Embedded in Wasted Food Was 2010 Trillion BTU in 2004 and 2030 Trillion BTU in 2007 agriculture transportation food handling food processing total energy, energy lost, energy lost, food [trillion BTU] [trillion BTU] [trillion BTU] [trillion BTU] 2004 [trillion 2004 [trillion 2007 [trillion category [j] (i ) 1) (i ) 2) (i ) 3) (i ) 4) BTU] %wasted BTU] BTU] grains [1] 71.4 185 426 155 838 32% 268 271 vegetables [2] 53.5 407 935 178 1580 25.3% 381 379 fruit [3] 26.9 270 619 122 1040 23.4% 234 243 dairy [4] 234 273 627 229 1360 32% 436 441 meat, poultry, fish [5] 778 284 652 238 1950 16% 312 316 eggs [6] 97.1 32.0 73 27 229 31.4% 72.0 72.9 dry beans, peas, 8.89 6.5 15 5 35.6 15.9% 5.67 5.74 and lentils [7] tree nuts and 0.33 9.8 23 8 40.9 15.9% 6.50 6.58 peanuts [8] caloric sweeteners [9] 0 137 314 115 566 30.5% 173 175 fats and oils [10] 0 85.4 196 72 353 33.4% 118 119 total 1270 1690 3880 1150 7980 2010 ( 160 2030 ( 160 Wasted dairy represented the greatest amount of energy waste of any food category. the relative energy intensity of food processing by food represents a significant amount of lost energy through category is in Table 5. food waste. The energy discarded in wasted food is more For the food handling step (i ) 4) we also define A as than the energy available from many popular efficiency 4j the percent of total mass as defined for the transportation and energy procurement strategies, such as the annual step (see Table 4 and 6, A ) A ). The amount of energy production of ethanol from grains (37, 38) and annual 4j 2j required to refrigerate, cook, and package food can be linked petroleum available from drilling in the outer continental to its density and size, thus we expect the percent of total shelf (39). Consequently, the energy embedded in wasted mass to be a reasonable estimate of A . food represents a substantial target for decreasing energy 4j The relative energy intensity (A ) was combined with the consumption in the U.S. A decrease in food waste must ij energy required for each food production step (E ) using eq be accompanied with a retooling of the food supply chain 3 to calculate the energy required for each food category at to ensure that the energy consumed during food produc- each production step. These calculations are summarized in tion does in fact decrease with a decrease in food waste. Tables 3-6. In these tables the energy for each food A study of the economics, feasibility, and policies necessary production step is converted from 2002 values (given in Table to achieve energy savings by decreasing food waste would 1) to 2004 values using the ratio of the total energy used in be valuable but is beyond the scope of this work. 2004 (100,400 trillion BTU (18)) to the energy use in 2002 Though we were able to estimate the energy required to (97,900 trillion BTU (18)). produce the food consumed in the U.S. and the energy The last columns in Tables 3-6 are combined with the embedded in wasted food, the data used were incomplete food waste percentages in Table 2 to calculate the embedded and out of date, likely representing a lower bound on the energy in wasted food as outlined in eq 4 (see Table 7). Table actual value. Further research is necessary to obtain more 2 contains food loss factors for processed fruits and vegetables recent and accurate accounts of the energy used in fisheries, (16% and 15.8%, respectively), which we use for the fruit and aquaculture, food packaging, disposal, and commercial food vegetable categories for the food processing step in Table 7 preparation. An updated and comprehensive study of food and then added into the total estimate for energy lost due waste in the U.S. food system accounting for waste in the to food waste for the respective food categories. fishing industry, on the farm, and during food processing is also necessary. Discussion Supporting Information Available From this analysis we concluded that the food wasted in Complete methodology and calculation of the energy re- the U.S. in 2007 represents approximately 2030 ( 160 quired to produce food for domestic consumption and for trillion BTU (the error for 2004 and 2007 is roughly the the relative energy intensity values for the agriculture same due to rounding) of embedded energy. The wasted production step. This material is available free of charge via energy calculated here is a conservative estimate both the Internet at http://pubs.acs.org. because the food waste data are incomplete and outdated and the energy consumption data for food service and Literature Cited sales are incomplete (see the SI). We assign to the energy lost estimate an error of 20% to account for changes in (1) FAO. The State of Food and Agriculture; United Nations Food food waste from 1995 and for the assumptions made in and Agriculture Organization: 2008. 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Sugar and Sweeteners Yearbook Tables; U.S. Department 11, 2009. of Agriculture Economic Research Service: 2009. (18) EIA. Annual Energy Review 2007; Energy Information Admin- (35) ERS. Feed Grains Database; U.S. Department of Agriculture istration: 2007. Economic Research Service: 2009. (19) NOAA. Aquaculture in the United States. 2009. Available at (36) Eshel, G.; Martin, P. A. Diet, Energy, and Global Warming. Earth http://aquaculture.noaa.gov/us/welcome.html (accessed Feb- Interact. 2006, 10 (1), 1–17. ruary 6, 2009). (37) RFA. Ethanol Industry Statistics. Available at http://www. (20) ERS. Aquaculture Data: Vol. and value of U.S. imports of selected ethanolrfa.org/industry/statistics/ (accessed June 19, 2009). fish and shellfish products; U.S. Department of Agriculture: 2009. (38) EIA. Ethanol. Available at http://www.eia.doe.gov/oiaf/ (21) BTS. 2002 Commodity Flow Survey; U.S. Census Bureau and ethanol3.html (accessed June 18, 2009). Bureau of Transportation Statistics: 2002. (39) EIA. Impacts of Increased Access to Oil and Natural Gas Resources (22) EIA. Energy Efficiency Report: The Transportation Sector; Energy in the Lower 48 Federal Outer Continental Shelf; Energy Information Administration: 1999. Information Administration: 2007. (23) CBO. Energy Use in Freight Transportation; Congressional Budget Office: 1982. ES100310D VOL. 44, NO. 16, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 6469 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environmental Science & Technology Pubmed Central

Wasted Food, Wasted Energy: The Embedded Energy in Food Waste in the United States

Environmental Science & Technology , Volume 44 (16) – Jul 21, 2010

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Pubmed Central
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Copyright © 2010 American Chemical Society
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0013-936X
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1520-5851
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10.1021/es100310d
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Abstract

Environ. Sci. Technol. 2010, 44, 6464–6469 system are available, and, despite the enormous energy Wasted Food, Wasted Energy: The investment we make in food production, the USDA reports that about 27% of available food was wasted in 1995 (8). Embedded Energy in Food Waste in This estimate does not include food wasted on the farm, in fisheries, and during processing and relies on outdated the United States food consumption and waste data, some of which is from the 1970s. Because of economic and population growth, AMANDA D. CU ELLAR the total amount of food production and consumption Center for International Energy and Environmental Policy, has grown since the latest food loss study for 1995 (9), and The University of Texas at Austin the portion of income Americans spend on food has dropped (10, 11). Consequently we expect the current MICHAEL E. WEBBER* amount of food wasted to be higher both relatively and Mechanical Engineering, Center for International Energy and absolutely as compared to the USDA’s 1995 estimates. Since Environmental Policy, The University of Texas at Austin food production requires about one-tenth of the energy consumed annually in the U.S., the energy embedded in wasted food might also correspond to a significant portion Received January 28, 2010. Revised manuscript received of energy consumption in the U.S. and represents an June 15, 2010. Accepted July 2, 2010. opportunity for avoided energy consumption. Because of the desire to reduce greenhouse gas emissions, concerns about fossil fuel availability, and the expected This work estimates the energy embedded in wasted food increase in population (12), the reliance of food on fossil annually in the United States. We calculated the energy intensity energy sources has become more scrutinized. In order to better understand the relationship between food and energy, of food production from agriculture, transportation, processing, a current estimate for the energy embedded in food produc- food sales, storage, and preparation for 2007 as 8080 ( 760 tion is needed as well as a calculation of the energy that is trillion BTU. In 1995 approximately 27% of edible food was wasted. lost in wasted food. No such study using current data has Synthesizing these food loss figures with our estimate of been identified in the literature. Consequently this work seeks energy consumption for different food categories and food to fill that knowledge void and provide important data that production steps, while normalizing for different production will quantify both the energy required to produce food in the volumes, shows that 2030 ( 160 trillion BTU of energy were U.S. in 2007 and the energy embedded in wasted food. embedded in wasted food in 2007. The energy embedded in This work will calculate the amount of energy used to wasted food represents approximately 2% of annual energy produce food from agriculture, through transportation, consumption in the United States, which is substantial when processing, retailing, and finally for preparation and con- compared to other energy conservation and production proposals. sumption. These data will then be combined with food loss To improve this analysis, nationwide estimates of food waste factors from the USDA (8) to calculate the energy lost in wasted food. Because the data available on food production and an updated estimate for the energy required to produce food and food waste are from different years, all data will be for U.S. consumption would be valuable. considered as a percentage of annual energy production for that year and extrapolated to obtain an estimated 2007 energy Introduction value. Energy for Domestically Consumed Food. First, we Recent food shortages, blamed in part on the growth of the calculated the energy required to produce food. Despite biofuels industry (1, 2), have created a new awareness of the various literature sources that estimate the energy required relationship between food and energy. Food is not only a for U.S. food production (5, 7, 13, 14), we recalculated this form of energy but also a consumer of fossil energy in its value for 2007 to generate an estimate organized in a way production, transportation, and preparation. Historically this that is compatible with the available food waste data. For has been a positive relationship: the last 50 years have seen our estimate of the energy required to produce food increased agricultural productivity thanks to the adoption of consumed in the U.S. we compiled data from various sources new technologies and inputs (3), which are largely based on including government reports and scientific literature. Data fossil fuels. The increase in the energy intensity of agriculture for the energy consumed in food production is mostly from has brought with it unprecedented yields with minimal the year 2002, whereas the available data on food loss is from human labor. Productivity improvements have been achieved 1995 and food quantities are given for 2004. In order to through a variety of means, including mechanization of the minimize error, the energy values for food production were agriculture sector, improved fertilizers, more resilient crops, determined for 2002 and then scaled to estimate 2007 values. and the development of pesticides (4), all of which rely on A summary of the results is shown in Table 1, along with the fossil fuels. year of the data source and citation. The Supporting Prior estimates for the amount of energy consumed by Information (SI) contains details of our methodology. the United States (U.S.) to produce food range from 10.5% While we expect that all values listed in Table 1 have (5) to 14.5% (6) of annual energy consumption. The newest significant uncertainty, none of the published data include estimate, released in March of 2010, estimates that 15.7% error estimates. A range of error is not given in Table 1 of energy consumption in 2007 was used to produce food unless we have multiple estimates for a single value in (7). Despite the significance of the food system as an energy Table 1 in which case we use the standard deviations of consumer, few estimates for the energy intensity of the the multiple estimates to approximate the error. For other listings, in Table 1 when we have a single estimate (that * Corresponding author e-mail: webber@mail.utexas.edu. Current is, for all categories except transportation and nitrogenous address: Department of Mechanical Engineering, 1 University Station C2200, The University of Texas at Austin, Austin, TX, 78712. fertilizers included in agricultural chemicals, fuel, and 6464 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 16, 2010 10.1021/es100310d  2010 American Chemical Society Published on Web 07/21/2010 a TABLE 1. Food Production in 2002 Required at Least 7790 ± 732 Trillion BTU in the U.S. food production steps [index ) i] energy [trillion BTU] year source ag. chemicals, fuel, electricity 1160 ( 69 2002 (adjusted) see the SI fisheries 18 2000/2002 (15–17) aquaculture, domestic 8.8 2002 (adjusted) (18, 19) aquaculture, imported 55.8 2002 (adjusted) (18, 20) agriculture total [1] 1240 ( 70 transportation, all modes 1650 ( 520 2002 (adjusted) (13, 18, 21–25) transportation total [2] 1650 ( 520 food processing 1120 2002 (18) processing total [3] 1120 ( 220 food services and sales 1530 2003 (26) packaging 684 2002 (adjusted) (5, 18) residential energy consumption 1570 2001 (5, 18, 27) food handling total [4] 3780 ( 460 total 7790 ( 730 The food handling step was the biggest contributor to the total. The index “i” is used as an index for the four different food production steps for the calculations using eqs 1 through 4 and equation S11 (see above and the SI for more information). electricity, see the SI for details) we use a 20% uncertainty also use a more complex method for scaling their food because it is the average of the error estimates that we energy estimates to different years, which does not assume were able to calculate for nitrogenous fertilizers (8% error) linear energy growth in the food system in line with total and transportation (32% error). Ultimately, the 20% error energy use in the U.S. bars we use are arbitrary, since they rely on two varying The energy required to dispose of food waste was not estimates of error for nitrogenous fertilizer production and included in this study. Food scraps made up 12.4% of total food transportation. We expect our energy estimate to have municipal solid waste generated in 2006 (28), but a value some range of error because of the assumptions and for the energy required for municipal solid waste disposal estimates we make throughout our analysis. Nonetheless, was not found in the literature. Compared to the estimates we rely on methodologies published in the scientific from the Heller et al., Pimentel et al., and Canning et al. literature and data sets from the U.S. government, which publications, the energy estimate presented here is lower we consider reliable sources. Therefore we use the 20% but within 25% of Heller’s work. Consequently, the energy error bars to not overstate the accuracy of our estimate estimate presented in Table 1 can be considered a lower but also to not undermine the validity of our work in bound estimate of the energy required for food production, estimating the energy required to produce the food consumption, and disposal. consumed in the U.S. Using this method for estimating Energy Embedded in Wasted Food. To calculate the error for individual values we calculate the total uncertainty energy embedded in wasted food we use 1995 food loss data in the energy consumption in 2002 to be (730 trillion BTU provided by the USDA for ten food categories, shown in Table after propagating the calculated and 20% error values 2. These data show that grain products, dairy products, fresh throughout all calculations. [To estimate total uncertainty, vegetables, fresh fruit, and fats and oils are, proportionally, 2 1/2 we used the following relationship: U ) (∑u ) , where the most wasted foods. tot i U is the total uncertainty and u is the uncertainty for The USDA report calculates food loss by retail and food tot i each of the steps listed in Table 1.] The energy estimate service establishments and by consumers. As the authors for food production scaled to 2007 energy values is 8080 of the USDA report note, there are significant food losses ( 760 trillion BTU. In 2002 and 2007 the total energy from other components of the food processing chain that consumption for the U.S. for all sectors was 97,900 trillion are not accounted for. These include losses on the farm, BTU and 101,600 trillion BTU, respectively (18). These from fishing, and during processing. Fishing waste could values were used to scale the energy for food from 2002 be a significant contributor to overall food waste; it is to 2007 assuming linear increases in energy consumption estimated that worldwide approximately 23% of fish for the U.S. and for food production. landings are bycatch, which are thrown back into the ocean, Our estimate for the energy required to produce the usually already dead or dying, instead of being sold and food consumed in the U.S. amounts to approximately 8% consumed (29). The 1997/95 USDA report also makes use of the energy consumed annually for all uses. Heller and of food waste factors from previous reports, some from Keoleian calculated the energy consumed to produce food the 1970s. The USDA applied food loss factors to food throughout its lifecycle for the late 1990s as 10,200 trillion availability data for 1995 to arrive at the percentage results BTU (5), constituting 10.5% of annual energy consumption. shown in Table 2 (5). The methodology used as well as the Pimentel et al. report in 2003 that 14.5% of the U.S. annual age of the food loss estimate implies a large margin of energy consumption is used to produce food; the year for error in these data both for 1995 and for the current the Pimentel estimate is not clear (6). In a 2010 report analysis. We expect that current food loss in the U.S. is Canning et al. found that food production required 15.7% greater (absolutely) than the amount estimated in the 1995 of 2007 energy consumption in the U.S. The Canning USDA work, but assume, for our calculations, that the estimate includes energy estimates for the same steps and relative food waste percentages are the same in 2007 as categories of the food system as we do but draws a larger for 1995. It is possible because of economic growth and boundary around the food system than our study does. the declining price of food as a portion of discretionary For example, Canning’s report includes several energy income that relative food waste percentages actually inputs that we did not include, such as the energy used increased over that time span. Due to unaccounted food by consumers to purchase food (fuel for driving to food losses and the potential for increased waste due to stores), and the energy required to produce modes of economic conditions we expect the results in the present transportation used in food procurement. Canning et al. analysis to represent a lower bound. VOL. 44, NO. 16, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 6465 E ) E (1) tot ∑ i TABLE 2. The USDA Estimates That 27% of Edible Food Was Wasted in 1995 with Fresh Foods (Fruit, Vegetables, and Dairy Products) and Fats and Oils Being the Most Wasted Equation 1 states that the energy consumed to produce Food Categories (8) food is equal to the sum of the energy required for each production step (E ), i, shown in Figure S1 and listed in Table edible food 1. For eq 1 the energy intensity (and therefore embedded commodity supply total loss % of total energy in wasted food) also varies by food category. Con- [index ) j] [billion lbs] [billion lbs] [%] (f ) sequently we rewrite eq 1 to account for the differences in grain products [1] 45.6 14.6 32.0 energy intensity between food categories as eq 2 fruit [2] fresh 22.4 7.2 32.0% E ) E (2) processed 25.9 4.2 16.0% tot ∑ ∑ ij i j total fruit 48.3 11.3 23.4% vegetables [3] In eq 2 the total energy for food production is the sum fresh 36.8 11.8 32.0% of the energy required to produce each food category, j (listed processed 26.2 4.2 15.8% total vegetable 63.1 15.9 25.3% in Table 2), at each production step, i. However, values for dairy products [4] E are not available in the literature, and thus they must be ij fluid milk 54.5 17.4 32.0% deduced. Consequently we replace E with the total energy ij other dairy products 21.8 7.0 32.0% required for each production step i and the relative energy total dairy 76.3 24.4 32.0% intensity for food category j and production step i, A ,as ij meat, poultry, and fish [5] shown in eq 3 red meat 30.4 4.9 16.0% poultry 17.1 2.7 16.0% fish and seafood 4.0 0.64 16.0% E ) E A (3) tot ∑ ∑ i ij total meat 51.5 8.2 16.0% i j eggs [6] 7.9 2.5 31.4% dry beans, peas, 2.3 0.36 15.9% When we include the fraction of food lost in each category and lentils [7] (f ) in eq 3 we obtain an estimate for the energy embedded tree nuts and 1.9 0.30 15.9% in wasted food (E ) as shown in eq 4 loss peanuts [8] caloric sweeteners [9] 38.8 11.9 30.5% E ) E A f (4) fats and oils [10] 20.3 6.8 33.4% loss ∑ ∑ i ij j i j total 27.0% 356 96.3 (of total) In eq 4 E and f can be determined by normalizing and a i j The index “j” is used as an index for the ten different scaling values published in the literature, as shown in Tables food categories for the calculations using eqs 2 through 4, 1 and 2. In this section we will develop reasonable estimates S1 through S4, and S8 through S11 (see above and the SI for A , which we will then use to calculate the total energy ij for more information). The term “f ” is used to denote the embedded in wasted food. fraction of the total production for food category “j” that is wasted. We calculate A in three different ways for the different ij production steps. In agriculture some products are far more energy intensive than others. For instance, the production To calculate the energy embedded in wasted food we will of animal products requires energy to grow the animal’s feed calculate the energy required at each of the four food produc- and must account for efficiency losses in the animal when tion steps (shown in Table 1 as i ) 1to i ) 4) to produce food converting feed to edible mass. We use data from Pimentel in the ten categories (shown in Table 2 as j ) 1to j ) 10) and (30, 31) on the amount of energy necessary to produce a kcal then use the food loss percentages (f from Table 2) to calculate of protein energy for subcategories in eight different food the energy embedded in wasted food. First we define the energy categories (grains, fruits, vegetables, meat, dairy, eggs, dry consumed annually for food production (E )ineq1 beans, peas, and lentils, and tree nuts and peanuts), and tot TABLE 3. Energy Required for the Agricultural Production (i = 1) of Food Categories for Different Food Categories Was Calculated Using Relative Intensity Factors and the Mass of Agricultural Products before Processing weighted average energy for food agriculture energy, food category energy intensity annual consumption production relative energy by food category [index ) j] by mass (e¯ ) [kcal/lb] [million tons] [trillion kcal] (E ) intensity (A ) [%] (E ) [trillion BTU] avg,j ij 1j 1j grains [1] 381 73.8 56.2 5.62 71.4 vegetables [2] 310 68.0 42.2 4.22 53.5 fruit [3] 259 41.0 21.2 2.12 26.9 dairy [4] 2220 41.5 184 18.4 234 meat, poultry, fish [5] 7070 43.3 613 61.3 778 eggs [6] 7840 4.88 76.5 7.64 97.1 dry beans, peas, 71.8 48.8 7.01 0.70 8.89 and lentils[7] tree nuts and 85.7 1.5 0.26 0.03 0.33 peanuts [8] caloric sweeteners [9] -- - 00 fats and oils [10] -- - 00 total, 2004 1000 1270 The total energy value for agriculture was scaled from the Table 1 value for 2004, the year of this analysis. 6466 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 16, 2010 TABLE 4. Energy Required for Transportation (i = 2) by Food TABLE 5. Energy Required for the Processing of Food (i =3) Category Was Calculated for 2004 Using the Mass-Based Was Calculated Using Adjusted Mass Based Relative Energy Relative Energy Intensity Values Intensity Values To Account Only for Foods That Undergo Processing before Sale transportation mass of food relative energy energy, by food food processing [million intensity category (E ) 2j mass relative energy energy, by food food category [j] tons] (A ) [trillion BTU] 2j food [million intensity category (E ) 3j grains [1] 28.3 0.11 185 category [j] tons] (A ) [trillion BTU] 3j vegetables [2] 62.2 0.24 407 grains [1] 28.3 0.14 155 fruit [3] 41.2 0.16 270 vegetables [2] 32.5 0.16 178 dairy [4] 41.6 0.16 273 fruit [3] 22.3 0.11 122 meat, poultry, fish [5] 43.3 0.17 284 eggs [6] 4.9 0.02 32.0 dairy [4] 41.6 0.20 229 dry beans, peas, 1.0 0.004 6.5 meat, poultry, fish [5] 43.3 0.21 238 and lentils [7] eggs [6] 4.9 0.02 27 tree nuts and 1.5 0.006 9.8 dry beans, peas, 1.0 0.005 5 peanuts [8] and lentils [7] caloric sweeteners [9] 20.9 0.08 137 tree nuts and 1.5 0.007 8 fats and oils [10] 13.0 0.05 85.4 peanuts [8] total, 2004 258 1690 caloric sweeteners [9] 20.9 0.10 115 fats and oils [10] 13.0 0.06 72 food mass data obtained from the USDA Economic Research total, 2004 209.3 1150 Service (9, 32–35) to calculate the relative energy intensity These values are scaled to represent 2004 energy of each category. For this analysis we were only able to locate consumption. energy intensity values for seventeen food subcategories in the literature. To calculate the energy intensity of the food categories used in this report we first list all of the subcat- TABLE 6. Energy Required for Food Handling (i = 4) by Food egories for which we have data and calculate their energy Category Was Calculated for 2004 Using the Mass Based intensities per mass using the Eshel Martin methodology Relative Energy Intensity Values (detailed in the SI) (36), and then we calculate a weighted average of the energy intensities of the subcategories to relative food handling represent the average energy intensity of the eight food energy energy, by food categories. We used this methodology to mitigate skewing food mass of food intensity category (E ) 4j of the food category energy intensity by an unrepresentative category [j] [million tons] (A ) [trillion BTU] 4j food subcategory and to calculate representative energy grains [1] 28.3 0.11 426 intensity for the entire food category. We use 2004 data for vegetables [2] 62.2 0.24 935 this calculation, thus the results are considered to be for the fruit [3] 41.2 0.16 619 year 2004. The final relative energy intensity values for dairy [4] 41.6 0.16 627 agriculture (A ) are summarized in Table 3. A detailed account 1j meat, poultry, fish [5] 43.3 0.17 652 of our methodology for calculating the relative energy eggs [6] 4.9 0.02 73 intensity of each food category for the agriculture production dry beans, peas, 1.0 0.004 15 step is given in the Supporting Information (SI) that ac- and lentils [7] companies this work. tree nuts and 1.5 0.006 23 The relative energy intensity of each food category for peanuts [8] caloric sweeteners [9] 20.9 0.08 314 agriculture is calculated from the weighted average of the fats and oils [10] 13.0 0.05 196 energy intensity of the food subcategories listed in Table S10 total, 2004 258 3880 and the mass of each food category consumed annually (listed in Table S11). It is important to note that the energy intensity values the amount of food that is produced, since food transporta- from Pimentel used in this study account for the energy used tion is mass-dependent and measured in ton-miles. The mass to produce agricultural inputs to the agriculture sector such of food in Table 4 differs from the masses used to calculate as livestock feed from corn. Therefore, to avoid double- A (shown in Table S10) because it accounts for food in its ij counting, we did not include livestock feed in our analysis finished form (as reported in the USDA Food Availability as it is already accounted for in the energy intensity factors Report for 2004 (9)), rather than in its raw form (for example, used. Also, throughout this study we consider food to be the sugar cane is classified as a vegetable in Table S10 and as a primary product of the agriculture sector. See the SI for more caloric sweetener in Table 4). The calculation of the relative details on our full methodology and considerations. energy intensity for food transportation by food category is Data for the food categories ‘caloric sweeteners’ and ‘fats shown in Table 4. and oils’ are not reported in the Pimentel et al. works; these The A (i ) 3 is for food processing) term used for the 3j omissions are logical since caloric sweeteners and fats and energy consumed in food processing was calculated using oils are made from primary agricultural products, which are mass ratios with the mass of processed fruits and vegetables included in this analysis. We include soy for human used in place of the total mass of these two food categories. consumption (32, 33), corn for processing (35), and sugar In the food availability report the USDA separates fruits and crops (34) into the dry beans and vegetable categories, vegetables that are processed and those that are sold fresh respectively, to account for the missing categories, as a (9). We expect that fruits and vegetables sold fresh have no portion of these crops are used to produce fats, oils, and or minimal processing. Food processing includes such varied sweeteners. operations as grain milling, canning, slaughtering, and all For food transportation we define A (where i ) 2isfor other modes of food preparation. Nearly all food goes through 2j transportation) as the ratio of the mass of a given food some form of processing; consequently we used mass ratios category to the total mass of food production. We assume for A and only included the mass of fruits and vegetables ij that the energy intensity of food transportation depends on that the USDA (9) reports as processed. The calculation of VOL. 44, NO. 16, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 6467 a TABLE 7. Energy Embedded in Wasted Food Was 2010 Trillion BTU in 2004 and 2030 Trillion BTU in 2007 agriculture transportation food handling food processing total energy, energy lost, energy lost, food [trillion BTU] [trillion BTU] [trillion BTU] [trillion BTU] 2004 [trillion 2004 [trillion 2007 [trillion category [j] (i ) 1) (i ) 2) (i ) 3) (i ) 4) BTU] %wasted BTU] BTU] grains [1] 71.4 185 426 155 838 32% 268 271 vegetables [2] 53.5 407 935 178 1580 25.3% 381 379 fruit [3] 26.9 270 619 122 1040 23.4% 234 243 dairy [4] 234 273 627 229 1360 32% 436 441 meat, poultry, fish [5] 778 284 652 238 1950 16% 312 316 eggs [6] 97.1 32.0 73 27 229 31.4% 72.0 72.9 dry beans, peas, 8.89 6.5 15 5 35.6 15.9% 5.67 5.74 and lentils [7] tree nuts and 0.33 9.8 23 8 40.9 15.9% 6.50 6.58 peanuts [8] caloric sweeteners [9] 0 137 314 115 566 30.5% 173 175 fats and oils [10] 0 85.4 196 72 353 33.4% 118 119 total 1270 1690 3880 1150 7980 2010 ( 160 2030 ( 160 Wasted dairy represented the greatest amount of energy waste of any food category. the relative energy intensity of food processing by food represents a significant amount of lost energy through category is in Table 5. food waste. The energy discarded in wasted food is more For the food handling step (i ) 4) we also define A as than the energy available from many popular efficiency 4j the percent of total mass as defined for the transportation and energy procurement strategies, such as the annual step (see Table 4 and 6, A ) A ). The amount of energy production of ethanol from grains (37, 38) and annual 4j 2j required to refrigerate, cook, and package food can be linked petroleum available from drilling in the outer continental to its density and size, thus we expect the percent of total shelf (39). Consequently, the energy embedded in wasted mass to be a reasonable estimate of A . food represents a substantial target for decreasing energy 4j The relative energy intensity (A ) was combined with the consumption in the U.S. A decrease in food waste must ij energy required for each food production step (E ) using eq be accompanied with a retooling of the food supply chain 3 to calculate the energy required for each food category at to ensure that the energy consumed during food produc- each production step. These calculations are summarized in tion does in fact decrease with a decrease in food waste. Tables 3-6. In these tables the energy for each food A study of the economics, feasibility, and policies necessary production step is converted from 2002 values (given in Table to achieve energy savings by decreasing food waste would 1) to 2004 values using the ratio of the total energy used in be valuable but is beyond the scope of this work. 2004 (100,400 trillion BTU (18)) to the energy use in 2002 Though we were able to estimate the energy required to (97,900 trillion BTU (18)). produce the food consumed in the U.S. and the energy The last columns in Tables 3-6 are combined with the embedded in wasted food, the data used were incomplete food waste percentages in Table 2 to calculate the embedded and out of date, likely representing a lower bound on the energy in wasted food as outlined in eq 4 (see Table 7). Table actual value. Further research is necessary to obtain more 2 contains food loss factors for processed fruits and vegetables recent and accurate accounts of the energy used in fisheries, (16% and 15.8%, respectively), which we use for the fruit and aquaculture, food packaging, disposal, and commercial food vegetable categories for the food processing step in Table 7 preparation. An updated and comprehensive study of food and then added into the total estimate for energy lost due waste in the U.S. food system accounting for waste in the to food waste for the respective food categories. fishing industry, on the farm, and during food processing is also necessary. Discussion Supporting Information Available From this analysis we concluded that the food wasted in Complete methodology and calculation of the energy re- the U.S. in 2007 represents approximately 2030 ( 160 quired to produce food for domestic consumption and for trillion BTU (the error for 2004 and 2007 is roughly the the relative energy intensity values for the agriculture same due to rounding) of embedded energy. The wasted production step. This material is available free of charge via energy calculated here is a conservative estimate both the Internet at http://pubs.acs.org. because the food waste data are incomplete and outdated and the energy consumption data for food service and Literature Cited sales are incomplete (see the SI). We assign to the energy lost estimate an error of 20% to account for changes in (1) FAO. The State of Food and Agriculture; United Nations Food food waste from 1995 and for the assumptions made in and Agriculture Organization: 2008. (2) Liebreich, M.; Rodriguez, R.; Boyle, H.; Ramos, C. Research Note, arriving at the final energy estimate as we did in the initial Insight Services: Biofuels; New Energy Finance: 2008. estimate for the energy required to produce food consumed (3) USDA. Trends in US Agriculture; USDA National Agriculture in the U.S. In Table 7 the food category that requires the Statistics Service: 2006. greatest energy to produce is the meat, poultry, and fish (4) EPA. Demographics; U.S. Environmental Protection Agency: 2007. category. Nonetheless, the food categories with the greatest (5) Heller, M. C.; Keoleian, G. A. Life Cycle-Based Sustainability embedded energy in their waste are dairy and vegetables. Indicators for Assessment of the U.S. Food System; University of Michigan: Ann Arbor, 2000. This discrepancy results from the greater proportional (6) Pimentel, D.; Pimentel, M. 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Published: Jul 21, 2010

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