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Energy use in food processing for nutrition and development
David Pimentel and Marcia Pimentel
College of Agriculture and Life Sciences and Division of Nutritional Sciences, Cornelll University, Ithaca, New York, USA
For about half the time human beings have existed on earth they ate only uncooked food. About 500,000 years ago fire was controlled and could be used to heat and preserve foods. Most food crops are produced during a relatively short growing season, and the abundant, often highly perishable, harvests must be preserved for consumption during the long non growing season. The use of various preservation methods has augmented the food supply and, obviously, the nutrients available to a given population group.
In addition to improving the reliability of the food supply, heating foods makes many more palatable or easier to eat. For instance, the flavour of meat is enhanced by cooking it, and the flavour and consistency of most cereal grains are improved by heating, which gelatinizes their starch content and makes carbohydrates more digestible. Although not all vegetables are cooked, heating them, if carefully done, makes them more tender while preserving their natural colours and flavours. Certainly, cooking foods and mixtures of foods also increases the variety of food available at mealtime.
Adequate processing techniques eliminate many of the factors that cause food to spoil or become hazardous to human health. Heating food to 100°C destroys most harmful micro-organisms and parasites that are natural contaminants of food, including Staphylococcus and Salmonella, but Clostridium botulinum must be exposed to temperatures of 116°C (attained under pressure) to kill the heat-resistant spores. Heating pork products to an internal temperature of 66°C (77°C for microwave) will destroy Trichinella, a small parasitic worm which, if consumed by human beings, will produce larvae that migrate from the gut throughout the body and cause serious illness. Numerous protozoan and other worm parasites that contaminate food products may cause human illness if vegetables and fruits from gardens fertilized with human excrete are not cooked sufficiently. Although it is logical to associate such problems with primitive agriculture, they are also of concern today in areas where organic farming is not carefully practiced and where sewage disposal and water supplies are inadequately supervised.
Although preservation technologies have enabled human beings to increase both the quantity and variety of their diet from harvest to harvest, some processing technologies destroy valuable nutrients in foods (6). Actually, nutrient losses occur before and after as well as during processing. The extent of nutrient loss depends primarily on the physical and chemical characteristics of the major nutrients. Ascorbic acid, which is water soluble and easily oxidized, especially in the presence of heat and trace elements, is particularly vulnerable to many preservation technologies. Dark green, leafy vegetables, which provide major amounts of ascorbic acid to the diet, lose substantial amounts of it when exposed to heat and water. In contrast, the loss of ascorbic acid during pasteurization of milk is not a great nutritional concern because milk is not a major source of ascorbic acid in the human diet. Overall, preservation enhances the nutritional quality of a given food supply because it increases the amount of wholesome food available over time.
Energy, from sources as diverse as solar and fossil fuel, powers the various processing and preservation technologies used by human beings to preserve their vital food supply. In addition, energy is expended to package the preserved products. This paper focuses on the energy cost of major methods of cooking and preserving foods and of packaging materials used for food products.
FOOD PRESERVATION TECHNOLOGIES
Drying and Storage
Drying grains, vegetables, fruits, and meats to reduce the moisture level to 13 per cent or lower prevents the growth of harmful microorganisms and also lessens the chances of infestation by insects. Sunlight is an effective, cheap source of energy for drying; it has been used for centuries and continues to be popular. Throughout the world grains and legumes are the most widely dried foods. They are easily processed because most grains have a low moisture content on harvest and, thus, require little or no drying before being placed in storage. Seldom are grains harvested with more than 26 per cent moisture; thus, it is relatively easy to reduce this moisture levell to 13 per cent.
A simple way to dry small amounts (one to five tons) of grain is to spread the kernels thinly over a piece of heavy black plastic. During drying, the grain should be protected from rain showers and should be covered at night with another sheet of plastic to prevent mould growth. Another energy-efficient way to dry grain is to blow hot air through it. The hot air may be provided by attaching a small fan at the open end of a large black plastic sausage-like container. As the air is blown through the tube, it is heated to 10°C to 40 °C by the sun striking the black tube. Hot air (30 to 60 °C) for grain drying can also be produced using flat plate collectors, which are constructed by covering black plastic or another black surface with clear glass or plastic. Oriented toward the sun, the heated air can be collected and blown through the grain.
Corn harvested on the cob can be placed in a corn crib for drying. Screened cribs keep birds and rodents away from the corn while allowing the wind to blow through it. Usually, the crib is no wider than one to two metres to facilitate maximum air flow through the corn. In the tropics and subtropics dried corn must be removed from the crib, shelled, and placed in storage to prevent insect and other pest attacks. Although this procedure requires extra handling of the corn compared with harvesting it directly in the field, solar drying in a corn crib uses 33 per cent less energy than direct field harvesting of grain (9). With field harvesting the moisture-laden corn must be dried using fossil fuel before storage (9).
In contrast to solar drying, drying grain using fossil energy is energy intensive because the removel of water requires large inputs of energy. In the usual drying of grains with fossil energy, for instance, the removal of one litre of water requires an average energy input of 3,600 kcal (11). However, by using the appropriate temperatures, suitable quantity of grain, and time of exposure, Leach reports that it is possible to remove a litre of water from grain with about one-third the usual energy input (11). In surveying corn drying in the United States, Pimentel et al. (23) reported an energy input of 1,520 kcal per litre of water removed from corn. Put another way, 1,520 kcal are expended to reduce the moisture level of 7.4 kg of field harvested corn from 26.5 per cent to 13 per cent.
All these calculated energy inputs for removing moisture from foods are higher than the theoretical values for evaporating moisture. For example, the evaporation of one litre of water from an open container theoretically should require as little as a 620 kcal input (7). Two to six times as much energy is required in drying grain because the water must be removed from inside the cells of vegetables, fruits, and meat and is not as accessible as water in an open dish. In other words, barriers must be overcome in order to remove the water from food, and this requires extra energy.
Obviously, arid regions of the tropics are particularly suited for drying meats, vegetables, and fruits that contain 70 to 90 per cent moisture at harvest. Even then these products must be cut into thin slices (0.5 to 1 cm) unless they are already quite small, like grapes that easily dry into raisins.
Once the processed food is dry, it must be placed in a container that will prevent pest attacks during storage. Although most plastics will prevent birds, insects, and micro-organisms from gaining access to the stored food, protection from rodents requires more substantial materials such as concrete, sheet steel, or glass. Since these bulk storage units will last for 30 to 40 years, the energy input per unit of food stored in the bulk storage facilities is relatively small.
The energy inputs for constructing bulk storage units out of concrete, glass, or steel depends upon the size and design. The energy required per kilogram of concrete, glass, and steel is 550 kcal, 4,500 kcal, and 18,000 kcal, respectively. Although steel is more energy intensive than concrete per kilogram, the steel storage container is usually much lighter weight than concrete. Although a glass jar is heavier than a metal can, the energy input for a glass jar to store the same amount of food as a steel can works out to be similar (20).
Smoking and Drying
Drying by exposing food to smoke from a fire is another method of preservation that had its beginnings in primitive societies, yet continues to be used today. Fish, meats, and, to a lesser extent, grains and vegetables are the major foods preserved by this method. Basically, smoking preserves food in two ways. First, the heat of smoking dries or dehydrates the food, and second, the various tars, phenols, and other chemicals in the smoke are toxic to both microorganisms and insects. These same tars and phenols, of course, may be carcinogenic to humans.
In many developing countries, grains to be used by the farm family are hung from the ceiling of the kitchen area of the house where the smoke and heat from the open kitchen fire both dry and smoke the stored grain. However, for complete protection from pests, including rodents, the dry smoked food should be placed in a dry, tightly sealed container until used. Because the kitchen fires already are being used either to cook food or heat the dwelling, dry smoking other foods is a by-product and thus is not energy intensive.
To smoke thin strips of a one kilogram fish, about one kilogram of hardwood, such as hickory, is required. Adding sand to the hardwood chips keeps the fire smouldering and smoking. The energy input for smoked fish is estimated to be about 4,500 kcal per kilogram with most of the energy coming from the wood chips burned in the smoking process. Fuel wood is the primary fuel of most of the poor people of the world. Already there are shortages of fuel wood in many parts of the world; thus, this smoking technique may have limitations where fuel wood is becoming scarcer.
Fish, pork, and other meats have been preserved by salting for over 3,000 years (10). This food processing method is not employed as widely today as it has been in the past, perhaps because other methods make possible the preservation of a wider variety of foods. The principle of using salt for preservation is to dehydrate the food product by increasing the osmotic pressure to a level where the growth of microorganisms, insects, and other organisms is prevented.
Like solar-drying of foods in hot, sunny climates, salting requires a relatively small input of energy. Usually about one kilogram of salt is added per four kilograms of fish or meat to be salted and dried (8). The method requires an estimated 23 kcal per kilogram of fish, meat, or vegetables preserved (90 kcal of fossil energy is required to produce one kilogram of saltl (25).
The salted product can be stored by hanging it in a cool dry area or by placing it in a tight, dry container. Under warm, humid conditions the hydrophilic nature of salt causes the outside of the food to become moist and eventually drip salt water until finally the added salt is lost and the product spoils.
Before the salted fish or meat can be eaten, the salt must be removed by soaking and rinsing the food many times with fresh water. Even after the soaking and rinsing, there is usually a sufficient salt residue to give the fish or meat a noticable salty taste.
For people on a low-sodium diet, consuming salted products can be a problem. A kilogram of lightly salted, dedydrated (12 per cent water) codfish contains 51,180 mg of sodium, whereas fresh codfish (65 per cent water) contains only 1,107 mg (33). Even taking into account the differences in moisture content, there is still about 10 times as much sodium in the salted cod. With careful soaking, it might be possible to reduce this some.
Since Louis Pasteur proved that microorganisms, invisible to the eye, caused foods to putrefy and that this putrefaction was not spontaneous decomposition, various methods of heating foods to temperatures high enough to kill harmful micro-organisms have been used to make preserved food safe for human consumption. The basic process in canning foods is to heat the food to boiling or higher, pack, and completely seal it in sterilized containers. The precise processing temperatures and times used depend upon the acidity, density, and other characteristics of the particular foodstuffs being processed. Foods with a pH of 4.5 or higher require the high heat of pressure canners to ensure complete destruction of the Clostridium botulinum heat-resistant spore.
The energy inputs are substantial for preserving foods by canning and then placing them in a suitable package. For example, producing sweet corn on a US farm uses only about one-third of the energy used to process and place it in a steel container. Most of the energy expended in processing and packaging is for producing the steel can. To produce a 16 oz (455 g) can requires 1,006 kcal (table 1). Using a throw-away 16 oz glass jar requires 1,023 kcal for the package, or only slightly more than using a steel container.
The figure for canning in table 2 is for large-scale canning operations. If canning is done in the home or in small cottage industries, the energy inputs for processing are greater than listed. Energy inputs for processing can be expected to rise from a low of 575-750 to a high of 1,200 kcal per kilogram of food processed, which represents an increase of 30 to 50 per cent for small-scale processing compared with commercial operations. Reusable glass jars, however, can reduce the total energy inputs in home canning below those for large-scale operations, which use disposable jars. For example, a reusable jar for one kilogram of food requires an input of 3,750 kcal, compared with 2,250 kcal for the disposable jar. Assuming that the average number of times a jar is used five, then the mean energy input for the jar per unit of food canned would be only 750 kcal or a saving of about 1,500 kcal. Thus, even assuming a two-fold increase in energy for processing alone, the net saving for home processing and packaging would be nearly 1,000 kcal per kilogram of food.
TABLE 1. Energy Required to Produce Various Food Packages
|Wooden berry basket||69|
|Styrofoam tray (size 6)||215|
|Moulded paper tray (size 6)||384|
|Polyethylene pouch (16 oz, or 455 g)||559*|
|Steel can, aluminium top (12 oz)||568|
|Smail paper set-up box||722|
|Steel can, steel top (16 oz)||1,006|
|Glass jar (16 oz)||1,023|
|Coca-Cola bottle, non-returnable (16 oz)||1,471|
|Aluminium TV-dinner container||1,496|
|Aluminium can, pop-top (12 oz)||1,643|
|Plastic milk container, disposable (1/2gal)||2,159|
|Coca-Coia bottle, returnable (16 oz)||2,451|
|Polyethylene bottle (1 qt)||2,494|
|Polypropylene bottle (1 qt)||2,752|
|Glass milk container, returnable (1/2 gal)||4,455|
Source: Ref 1. * kcalculated from data in ref. 1.
In freezing, many of the desirable palatability and nutritional qualities of the fresh food are retained for relatively long periods of time. The temperatures employed of -18 C or below prevent the growth of harmful micro-organisms because water is unavailable for their growth. Fruits are frozen as a dry pack with added dry sugar or in a syrup. Vegetables must be blanched prior to freezing to inactivate plant enzymes that cause deterioration of naturel plant flavours and colours.
TABLE 2. Energy Inputs for Processing Various Products
|Beet sugar (assumes 17% sugar in beets)||5,660|
|Cane sugar (assumes 20% sugar in cane)||3,380|
|Fruit and vegetables (canned)||575|
|Fruit and vegetables (frozen)||1,815|
|Flour (includes blending of flour)||484|
|Dehydrated foods (freeze-dried)||3,542|
|Soft drinks (per litre)||1,425|
|Wine, brandy, spirits (per litre)||830|
Source: Ref. 2.
The energy inputs for freezing vegetables and fruits are significantly greater than for canning, averaging 1,815 kcal per kilogram of food frozen compared with only 575 kcal per kilogram for canning (table 2). There is a discrepancy because the canning process requires only heating, while the freezing may involve brief heating, cooling, and then actual freezing.
Furthermore, canned foods can be stored at room temperature or cooler, whereas frozen food must be kept in freezers at temperatures of -18 °C or lower. Maintaining such a low temperature requires about 265 kcal per kilogram per month of storage (32). Since frozen foods are usually stored three to six months, this energy cost must be added to the freezing cost, making the total energy input much greater than that for canning. The energy for six months of storage alone would be 1,590 kcal. The total expended for processing, packaging, and storing a frozen kilogram of food is 4,905 kcal, whereas for canning the total is 3,535 kcal per kg. Thus, freezing requires nearly 40 per cent more energy than canning.
An advantage of freezing is that packaging for frozen foods is often paper or plastic pouches, which require much less energy than the steel and glass containers required for canning (table 1). Freezing also retains more heat-labile nutrients and is less destructive to colour and flavours, especially those of fruits and vegetables.
In freeze-drying, a recently developed method of food drying, the food is first frozen and then dried under high vacuum. This method makes possible the attainment of a moisture content of 2 to 10 per cent (Senhaji, 1983, personal communication); the food is exceptionally light in weight and can be stored at room temperature. However, this process is even more energy-intensive than regular drying, because energy is used both for freezing and drying. Foods processed by this technology require 3,542 kcal per kilogram of product.
Although the energy input for freeze-drying is high, the energy input for the plastic pouch can be significantly below that for either a steel can or glass jar required for canning (table 2). Another advantage is the reduced transport costs of shipping dehydrated food. For example, meats are often 60 per cent water, and potatoes, 80 per cent water. If these were dehydrated to 1 per cent water, the shipping costs for long-distance trucking would about equal the energy input of dehydration. For example, one kilogram of canned potatoes requires a total energy input of 6,769 kcal (575 for processing, 2,210 for steel can, and 3,984 kcal for transport over 4,800 km). In comparison, one kilogram of dehydrated potatoes would require a total input of 6,237 kcal (3,542 for dehydration, 1,500 for the plastic pouch, and 1,195 kcal for transport over 4,800 km). Thus, the total energy input for dehydrated potatoes would be slightly less than that of canned potatoes transported the same distance.
Other Food Processing and Preparation Technologies
The energy inputs for preserved, processed, and home prepared foods are substantial. For example, in an analysis of the energy inputs of the production of a one kilogram loaf of white bread in the United Kingdom, Leach reported that 77 per cent of the 3,795 kcal total energy used to produce and market the bread is used in processing, i.e., 13 per cent for milling and 64 per cent for baking (11).
Analysis of US technology shows that producing a one kilogram loaf of white bread requires an input of 7,345 kcal, substantially greater than that reported for the United Kingdom. Milling and baking account for only 27 per cent of the total energy input, compared with 77 per cent in Leach's analysis. In contrast to the British system, the major energy input for the white bread produced in the United States is the 45 per cent expended for wheat grain production.
The energy inputs needed to produce a one-kilogram can of sweet corn differ greatly from those expended for a loaf of white bread. The energy for production of a can of corn amounts to only a little more than 10 per cent of the total energy used to produce, process, and market it. Most of the total energy input of 2,785 kcal for processing is expended for the production of the steel can. Specifically, the heat processing of the corn requires only 575 kcal, while the production of the can requires about 2,210 kcal. In the developed nations, foods that are processed are also shipped about 1,000 km, which requires significant inputs of energy.
The other large input that must be included in energy accounting for a given food is the energy expended by the consumer shopping for the food, especially in the developed nations. In the United States, food shopping usually requires the use of a 1,000-3,000 kg automobile. Based on an average load of 15 kg that includes the corn and the other groceries brought home from the supermarket, about 680 kcal are expended just to transport a can of corn home from the store. This energy expenditure is about three-quarters of the amount of energy (990 kcal) needed to produce the corn alone. Energy expended in home preparation amounts to 1,005 kcal, or about 12 per cent of the total and includes cooking the corn and using an electric dishwasher to clean the containers, plates, and other utensils that are used in cooking and serving the corn
All the energy inputs for producing, processing, packaging, transporting, and home-preparing a one-kilogram can of corn total 6,560 kcal. Contrast that with the 825 kcal of food energy provided by the corn. This means about eight kilocalories of fossil energy are expended to supply one kilocalorie of sweet-corn food energy at the dinner table.
Energy-accounting for the US food system is adversely affected by the practice of feeding most of the corn and other cereal grains suitable for human consumption to livestock. Of the estimated 1,300 kg of grain produced per capita per year in the United States, only about 110 kg (or 10 per cent) of the grain produced is consumed directly by humans (24).
The energy inputs for processing several other food products are also presented in table 2. The relatively large inputs for processing one kilogram of sugar, e.g., 3,380 kcal for cane sugar and 5,660 kcal for beet sugar, are due primarily to the energy used for the removal of water by evaporation. As indicated earlier in this section, the evaporation of water is an energy-intensive technology. Thus, one kilogram of crystalline sugar, which has a food-energy value of 3,850 kcal, requires almost that much in energy inputs to process.
The processing and preparation of breakfast cereals are also energy-intensive. On the average, they require about 15,675 kcal per kilogram of cereall produced. The energy inputs include those required for grinding, milling, wetting, drying, and baking of the cereals. Other technologies, like extrusion processes, which are sometimes used, also require relatively large inputs of energy. Although 15,675 kcal are used in the production of one kilogram of breakfast cereal, this amount of cereal provides only about 3,600 kcal of food energy.
Both chocolate and coffee concentrates are examples of energy-intensive food-processing techniques because of the energy used in roasting, grinding, wetting, and drying the product. The processing of one kilogram of chocolate or coffee is reported to require more than 18,000 kcal.
Another energy-expensive product is the soft drink because of the pressurized systems that are employed to incorporate carbon dioxide. A total of 1,425 kcal is expended per lithe of soft drink produced. Note how much less energy is used in the processing of milk, which requires about 354 kcal per litre.
PACKAGES FOR FOODS
In general, processed foods must be stored in some type of container. The energy expenditures associated with several different containers for bulk and small lots of food products have been mentioned earlier and were presented in table 1. For instance, frozen vegetables are usually placed in a small paper box or plastic pouch, requiring an expenditure of approximately 1,590 kcal or 1,230 kcal of energy respectively.
Although there is little difference between the energy inputs required for the production of steell cans and glass jars, the energy inputs needed to produce aluminium soft drink cans are significantly more. A 355 ml steel can for soft drinks requires about 570 kcal for production, while the same size aluminium can requires 1,643 kcal, or nearly three times as much energy. Note that the soft drink placed in that size can contains about 150 kcal of food energy in the form of sugar, which is equivalent to about 10 per cent of the energy expended in producing the aluminium can. A more extreme illustration is the high energy cost of an aluminium can made to contain a diet soft drink that has only one kilocalorie per 355 ml can. In total, the energy for processing and aluminium for the can is 2,213 kcal for the one-kilocalorie diet drink.
Another example of large energy input for food containers is the aluminium food trays commonly used to hold frozen TV dinners. An average tray requires about 1,500 kcal to make. Indeed, the amount of energy expended for the tray is often greater than the food energy that is in the food itself, which usually ranges from 800 to 1,000 kcal.
In addition, the diverse containers used to display fruits, vegetables, and meats in food markets require considerable energy for production. Energy expenditures range from about 70 kcal for wooden berry baskets to 380 kcal for a moulded paper tray.
Because of increased concern about the desirability of recycling beverage containers, the energy input for recycling milk and beverage bottles has been analysed. A disposable plastic half-gallon milk container requires 2,159 kcal to produce; a returnable glass container requires 4,445 kcal. With twice as much energy "invested" in the glass container, two uses of the returnable glass container are needed to equal the initial energy input for the plastic container. An average of five uses makes the returnables quite energy efficient. This is true even when the additional energy expended to collect, transport, sort, and clean the reusable container is included.
As with milk containers, returnable glass beverage bottles require more energy for production than do non-returnable bottles. A 16 oz returnable bottle requires about 2,450 kcal for production, compared with 1,470 kcal for the same size non-returnable bottle. Again, an average of five uses of the returnable bottle would make it extremely energy efficient.
Considering only the energy expended in the production of the bottle does not give a complete picture of the energy cost involved. Other factors, such as environmental pollution caused by non-returnable containers, must also be weighed along with energy expenditure before community policies can be decided upon. The current trend in developed nations is toward greater use of returnable containers.
COOKING AND PREPARING FOODS
Humans prefer to consume most foods-grains, meat, eggs, and to a lesser extent some vegetables and fruits-cooked rather than raw. Cooking and preparing foods for eating requires an expenditure of more energy in the food system.
In the United States, an estimated 10,270 kcal of fossil energy is used per person per day just for refrigerating and preparing food. This averages out to an estimated 5,320 kcal per kilogram of food prepared. These estimates assume that an average of 5 per cent of the total energy consumption per capita is expended for preparing and cooking food (24) and that each person consumes an average of 705 kg (1,550 lb) of food per year (34).
Depending on the food, the fuel used, the material of the cooking containers, the method of preparation, and the stove used, the energy input varies considerably. There appears to be little difference between the energy expended for baking, boiling, or broiling foods. This assumes that the exposure of the food to heat is optimal and that the cooking utensils allow for efficient heat transfer to the food itself. Note that not only the shape but also the reflective qualities of the cooking utensil, the viscosity of the food, and the skill of the cook affect the transfer of heat and influence cooking efficiency. These variables make it difficult to calculate precise energy expenditures, but it is important to acknowledge that they are part of energy accounting.
The transfer of heat from stoves to foods is relatively inefficient. For example, an electric stove is 75 per cent efficient, and a gas stove is 37 per cent efficient in transferring heat from the burner to the food (29).
Nevertheless, the gas stove is much more efficient overall than the electric stove for use in cooking because the energy needed for the production and transport of gas to the home accounts for only about 10 per cent of the energy potential of gas. This makes the production and transport of gas energy 90 per cent efficient. Multiplying the 90 per cent efficiency by the 37 per cent efficiency of transfer of heat to the item cooked yields a 33 per cent overall efficiency for gas cooking
For electricity the picture is more complex. First, mining and transporting coal reduces the energy potential of the coal by 8 per cent. This means the 92 per cent of the initial energy potential of the coal is available at the power plant for subsequent electric power generation. Assume that the power plant has an average efficiency rate of 33 per cent in converting coal to electricity, that the transmission of the electricity to the home is 92 per cent efficient, and the transmission of heat from electric stove to food is, at best, 75 per cent efficient. Then, taking into account the successive losses in potential energy that occur throughout the entire process (100 x 0.92 x 0.33 x 0.92 x 0.75), the overall efficiency rate of electricity is only 21 per cent. This means that cooking by electricity is only about two-thirds as efficient as gas.
Microwave cooking, characterized by high-frequency radiation, generates heat within a food through the friction created as food molecules are attracted and repelled by the microwaves. Compared with a 14 per cent efficiency for electric and 7 per cent for gas ovens, microwave ovens have been judged 40 per cent efficient in the direct transfer of energy to the food (31). These calculations do not take into account the mining, production, and transport of energy to the consumer. The US Department of Energy estimates that an average household would save only about US$10 per year in energy costs if a microwave oven were used (31). While the savings in energy cost may not be larger, microwaving is quick and convenient, and nutrient retention, especially in vegetables, is excellent (3).
Less efficient than either electricity or gas is cooking with charcoal or wood over an open hearth, as is commonly done in homes in developing nations. An open fire is only 8 to 10 per cent efficient in transmitting heat to the food (30). Contrast the 1,800 kcal required to cook one kilogram of food by a gas stove, with 6,000 kcal from wood burned in an open fire. Nearly twice as much energy would be used to cook a kilogram of rice (containing 3,500 kcal of food ) than is actually present in the food itself. This method, then, is both an inefficient and costly use of fuel. Using a simple woodburning stove with adequate controls would increase the energy efficiency to 20 to 30 per cent and thereby reduce the fuel cost.
Assuming an average 6,000 kcal per day for cooking, 520 kg (dry) of wood are burned per year person in a developing country. Openshaw (12) reported the average consumption of wood in developing countries ranges from 910 to 1,200 kg per year per capita, an estimate considerably higher than our minimum calculation of 520 kg per capita.
Cooking food in developing nations is responsible for nearly two-thirds of the total energy expended in the food system, while food production requires only about one-third of the total (table 3). Almost all of the energy used for cooking comes from renewable energy sources, primarily firewood and charcoal, and dung crop residues, which are burned over the open hearth.
TABLE 3. Model of Annual per Capita Use of Energy(kcal
in the Food Systems of Rural
Populations in Developing Countries
|Fossil Energy||Renewable||Energy Total|
From data in reds. 5, 14, 15, 17, 26, and 28.
Special mention should be made of charcoal, which is commonly used for cooking. True, cooking over an open charcoal fire is similar to using wood, having about 10 per cent efficiency in the transfer of heat energy to the food. however, charcoal production is extremely energy intensive. Although charcoal has a high energy content (7,100 kcal of energy per kilogram when burned), 28,400 kcal of hardwood has to be processed to obtain the 7,100 kcal of charcoal. Thus, there is only a 25 per cent efficiency in the conversion of hardwood kilocalories into charcoal kilocalories, and when charcoal is burned over an open fire, the overall efficiency in energy transfer is only 2.5 per cent (100 x 0.25 x 0.10). Indeed, this method is an extremely inefficient and costly way to transfer energy. Encouraging the use of charcoall for fuel defeats the conservation and efficient use of the renewable energy resources of wood forests (4).
LEARNING FROM OTHERS' MISTAKES
Developing nations would be well advised to look closely at the land use, preservation of environmental resources, pollution problems, and overuse of fossil fuels as well as nutritional problems that are characteristic of many industrialized nations. A careful examination of these serious problems may prevent developing nations from duplicating these costly and often harmful experiences.
Arable land is a prime world resource needed for food and fibre production, now and in the future. In the United States, for example, altogether too much fine agricultural land has been allowed to be degraded by soil erosion (13). Typical of the loss experienced is an instance in the state of lowa where one-half the topsoil has been lost in the last 100 years (27). Topsoil is replaced slowly, and even under the best farm management the passage of 200 to 300 years is required before one inch (2.5 cm) of topsoil is formed (19). Erosion has occurred because of a careless disregard by the public and government for maintaining the quality of farm lands. To date, no constructive policies to prevent soil erosion have been instituted on a national basis in the United States.
Water supplies, another vital resource needed for productive agriculture, are being expended at an alarming rate in many industrialized countries. At present in the United States, about 83 per cent of the water is consumed by agriculture, and an overwhelming percentage of this is being pumped from the vast aquifers at a rate much above the national recharge rate (35). Thus, this water resource is literally being "mined" or depleted for present-day agricultural production. This practice does not bode well for agricultural production in future decades. No effective policy is in place in the United States to conserve and protect the ground water resources, and until there is such a policy, the depletion of these natural stores will continue. Developing nations, aware of the possibility of such problems arising in their own countries, should consider implementing both policies and programmes to conserve their vital water supplies.
A study of the benefits and costs of the massive use of pesticides, now typical of most industrial nations, will benefit developing nations as they plan pest-control programmes for their own countries. In the United States over a billion pounds (500,000 tons) of pesticides are applied to crops each year (34). The use of these pesticides results in about 45,000 human poisonings annually, with about 3,000 people sick enough to require hospital care (21). In addition, livestock and crops have been killed or contaminated by these chemicals and, therefore, could not be utilized for food. Moreover, beneficial organisms, like parasites and predators, often are killed inadvertently, resulting in additional pest outbreaks that require additional applications of expensive pesticides. Also, about 415 major pests have developed resistance to pesticides, and these pests require larger quantities of costly pesticides for control. All too often the chemicals or their residues pollute soil and water (18).
The evaluation of both the successes and failures associated with pesticide use in developed nations is relevant to planning programmes for the future. Human beings everywhere will continue to battle the pests that are responsible for extensive crop losses and that spread deadly diseases. In all nations we hope that pest controls will be centred on an integrated pest management approach that will be safer yet provide the protection needed.
Another area of development less industrialized nations should carefully monitor is the heavy reliance on fossil fuels, as well as the many machines these fuels power. Perhaps developing nations can avoid the problems many industrialized nations are now experiencing as they face increasing energy costs and dwindling supplies of fossil fuels. Examples of these problems can be found in every sector of industrial economies. In the United States, only 10 hours of direct farm labour are needed to raise a hectare of maize. This is about 1/120 of the hours needed to raise a hectare of maize entirely by manpower (20). Obviously, in nations that have an abundance of labour or servious unemployment the replacement of manpower by fuel driven machines should not be allowed to expand to the levels characteristic of agricultural production in the United States and other developed nations.
The development of energy-saving methods for food processing, packaging, and distribution will be beneficial to less-developed nations. A careful evaluation of these processes as they now exist in the industrialized nations will provide helpful insights into their efficiency and cost in both dollars and energy. For example, the cost of packaging two crackers in a plastic pouch, which requires more energy than the energy available in the crackers, will be evident. Developing nations can consider whether their economy willl support the luxury of this special packaging, to take another example, of manufacturing a 12 oz soft drink containing only 1 kcal of food energy but requiring 2,200 kcal of fossil energy to produce (19).
Surely the aim of each country, now and in the future, is to provide all its citizens with an ample and nutritionally balanced diet. For developing nations this will mean an increase in available calories and, in many areas, major nutrients. The availability of food is influenced by many factors, including agricultural productivity, supply and demand, governmental policy, especially as related to export of foods, per capita income, distribution of foods, preservation of harvests, and greater nutritional knowledge.
Malnutrition, defined as under-nutrition or over-nutrition or an imbalance of nutrients, exists in both developing and developed nations. Thus, malnutrition occurs where food is scarce and where it is plentiful. In the United States, where food is abundant, obesity is a nutritional problem. Other conditions, such as arteriosclerosis, hypertension, and some cancers, are prevalent in the United States and have been associated with diets high in calories and high in fat, especially saturated fats, and high in cholesterol.
As developing nations seek ways to improve the nutritional status of their people, the effects of dietary patterns typical of industrialized nations like the United States should be carefully evaluated. Perhaps the typical high calorie and high animal protein diet with its accompanying high saturated-fat content should not be the nutritional goal of these countries. Instead, a moderate increase in animal products added to the basic diet of plant foods may prove to be the wiser choice.
The future projections for world population necessitate that all countries reassess their priorities for agricultural production so the food needs of people can be met. Land, water, and energy supplies (human labour, fossil-based, and even solar) all interact and will determine how successful production quotas can be achieved. Industrialized nations are having to re-evaluate their past programmes and priorities so they will be more productive in the future. Meanwhile developing nations have an advantage because they can profit from the mistakes of other nations and avoid the costly errors many have made.
Energy is expended in a myriad of human activities. Energy sources based on fossil fuels, which are non-renewable resources, have become a concern because their use has escalated dramatically in the past three decades, especially in the developed countries. This pressure is being felt not only in agricultural production but in food processing and, in fact, at all stages of the food chain.
Certainly, the safe preservation of abundant harvests to augment the human food supply and ensure a reliable source of nutrients is a vital priority in coming decades in order to meet the food needs of the rapidly expanding world population.
All facets of presently used preservation and packaging technologies merit a reassessment. Further research to develop methods that use less of our non-renewable resources and a more careful use of the renewable sources of energy must be prime aims of food technologists, who have a most important part to play in the continued wellbeing of the world's people.
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