The food industry is essentially the most important of all the energy industries, providing our most important fuel. The production of food is an energy conversion process and like all such processes has efficiencies associated with it. Modern agriculture has many inputs which have energy associations, the most fundamental: solar energy is converted to energy within plants very inefficiently (typically 0.1%, though this depends upon the availability of other inputs and the nature of the plant itself). In situations where food supply is not a problem and land use more relevant, these efficiencies might be compared with what are often also seen as the poor inefficiencies of converting solar energy into other energy 'crops' (ie all renewable energies, not only biomass).
The assessment of rational use of energy within the food industry must consider food production, processing and distribution together with associated industries and must consider the foods we eat compared to benchmark foods which represent efficient use of energy. Also important is the energy used within the home (and restaurant) for storage and final preparation. An overall analysis of the energy consumption at each stage is given below 
Table 3: Relative use of Energy within entire food production system 
These values are representative of the food we eat. Different proportions and overall energy totals may be achieved by considering the overall impact of changes in each sector.
What we eat
Table 4 represents average values, for the UK, of food consumed per person per day for the main food groups. In particular, the table provides the weight of each food type consumed per day and the energy which that quantity of food provides. The Estimated Average Requirement (EAR) of energy is given, based on an average of male and female values for the main adult age group (19-50 years) assuming an average level of activity. The third column represents the contribution towards the EAR made by each of the food groups for the given consumptions. The fourth column allows comparison of the same quantities of each food group to be made, illustrating the relative levels of energy provided by the different food groups.
Note that our food requirements must be based upon more than just our energy needs. Data relating to the definitions of each food group, contributions to other food requirements (protein, fibre, minerals, vitamins) are available in specified sources. A similar approach could be taken to examine the efficiency of different food products in supplying our other requirements.
Table 4: Average daily food intake within the home, UK, 1996 [32,33].
Energy efficiency in food production (Agriculture)
A full analysis of energy use in food production should look at different methods of production considering different levels of work (human, animal and machine energy inputs) as well as capital inputs (fertilizers, pesticides, machinery ...). This data is available in referenced sources [15,34]. Note that any one production method will not be appropriate to all locations. Presented here will only be data (input and output) for techniques practised in the developed world. Where available, this data will refer to the UK. The comparisons here are thus largely directed to comparison of efficiencies of different agricultural product groups rather than different techniques.
Note on calculation of efficiencies
The efficiencies given for the production of different foods represent the food (chemical) energy obtained from consumption to the energy used in production (fossil and human fuel). Overall efficiencies of the different foods will be much lower once the other components are taken into consideration. An efficiency of 100% represents an equal energy input to chemical food output. An efficiency below 100% represents a system which utilises more energy than we are able to obtain from it.
Excluding capital energy costs (for example: energy consumed in producing fishing boats), the efficiency of Sea Fishing is dependent on fish densities and distance travelled by fishing vessels. Depletion of stocks or extraction of a highly prized 'crop' create significant energy inefficiencies. Small scale fishing, in general, is much more efficient than large scale. Efficiencies of Western Sea Fishing varies from approximately 50% down to less than 0.5%.
Intensive Fish Farming energy costs include feed, pumping and fertilizers. Construction of the farms also involves significant capital energy expenditure. Energy efficiency of fish farming is generally within the range of Sea Fishing at between 10 and 1% efficiency.
The production of meat is another system for which the method of production has a very significant effect on the efficiency of conversion. Animals left to forage are able to convert vegetable matter which cannot be utilised (for the same purpose) by humans and some animals (particularly pigs) can be fed food wastes. In foraging systems, land use tends to be the dominant concern. Where animals are fed foods which are suitable for human consumption (mainly grains and legumes) efficiencies are much lower as the energy consumed in producing the feedstocks must also be taken into account. Much livestock production involves the use of both forage (typically cut and fed to the animals) and agricultural products for feed. Typical efficiencies for relatively intensive systems range from 0.5% to 10% (Foraging system).
Grain and Legume Production
Again, the more traditional production systems tend to be more efficient with systems relying almost entirely on human and animal energy having up to 1000% efficiencies. In systems relying mostly on human power, efficiencies below 100% would be nonsensical. High efficiencies can still be achieved under intensive systems, with human/animal energies being replaced by machinery. Intensive systems also have energy inputs associated with the production and use of fertilizers, pesticides and irrigation. Typical efficiencies for intensive systems range from 200 to 500%.
Fruit and Vegetables
In general fruit and vegetable production has efficiencies in between those of grains and livestock systems. Energy inputs depend on the crop and the system but machinery is usually predominant though fertiliser and pesticides use also contribute significant energy expenditure. In UK sugar-beet production, approximately 50% of the energy input is for fertilizer. Typical figures for US production range from about 20% through to over 150%. A slightly lower efficiency compared to grain crops.
Efficiency (energy out/energy in: %)
Table 5: Typical efficiencies for different Western agricultural systems 
Energy Efficiency in food processing and packaging
Most foods require some form of processing both to increase the useful life of the foods (destroy harmful microbes, parasites and toxins) as well as a means to improve flavour and digestion. This processing may be carried out by either the food industry, the consumer or both. The need for processing by the food industry tends to increase the further the final consumer is from the source of the food. This makes it sometimes difficult to separate food processing from the transport of foods. The processing of some foods, can make the energy required to produce the raw ingredients relatively insignificant. Thus it is important to consider not only the energy required to produce the 'raw' foodstuff but the combination of energies for production, transport, processing, packaging, distribution, storage, collection and final preparation. In many cases the magnitude of any one of these may be an order of magnitude above all the others.
Foods may be processed by industry to produce that same foodstuff in a different form or combined/processed with other foods. The main forms of processing (particularly for single foodstuffs) which increase the shelf life of the goods are canning, freezing, drying, salting and smoking. Of these, the latter two are less common and will not be considered.
Most food groups for which canning is suitable, may also be frozen. Drying is a feature of the preservation of grains and some fruit. Fruit is commonly preserved using either of the three methods.
Food energy represents an average for fruit and vegetables
Energy efficiency for production is 100%
Packaging data is for steel can and polyethylene pouch
Table 6: Typical energy required to produce a 16oz (455g) 'package' of canned and frozen fruit/vegetables 
As a generalization, canning is less energy intensive than freezing as both canning and freezing involve heating the food prior to packaging. However, freezing also includes cooling and freezing after the food has been blanched which add to the energy demand. However, the energy required for packaging is generally less for frozen food than canned but this benefit is usually negated by the energy required for storage. Frozen foods will continue to demand an energy input throughout their shelf life whereas canned food will not. Table 6 provides an example comparing the energy use in each of these processes.
Note that excluding the storage energy, canning and freezing require comparable energies. However, some storage is inevitable. A smaller package may result in relatively higher energy consumption for canning than freezing as a smaller can will require almost as much energy to produce. Best efficiencies are most likely achieved through the purchase of the large cans (assuming food is not wasted) and small amounts of frozen items stored in small, efficient freezers at a high replacement rate.
Whereas canning and freezing are associated with industrial processing (though they may take place at a small scale), the drying of foodstuffs may either be carried out in an industrial, high fuel intense way or by utilising solar energy. Drying is the easiest form of preservation available using renewable energy means.
The most efficient industrial drying processes require approximately 150kcal/kg to reduce the moisture level in grains to one at which insects and organisms will not thrive. Dehydration requires a much greater quantity of energy (typically 3500kcal/kg) as the process removes water from inside the cells. Freeze-drying has an energy demand between these two, resulting in a product, whilst not dehydrated, has a moisture level below that achieved with regular drying.
Table 7: Energy Required for Packaging Materials (KWhth/kg) 
Energy efficiency in food distribution
Energy related to food distribution will be influenced by the distances between the different nodes representing the sources of the raw foods or food ingredients, any production plants, and the centres at which transport vehicles are changed. It will also be influenced by the type of vehicles used for transportation and the efficiency with which they are used. Goods which require specific storage requirements, for example refrigeration, will also include an energy penalty which will be affected by duration of transportation as well as the means that storage is achieved and the efficiency of it.
The transportation of foodstuffs within the UK represents one third of all known road goods vehicle traffic (see Transport Section). There will be a contribution for transportation to the UK for many of the foodstuffs . Consumers have the luxury of being able to have any food at any time of the year and often that is provided at a great energy expense, particularly with perishable foods. For example, when a particular food is in short supply, for example at the start of its harvesting season, it may be financially viable to air freight it to countries where it would have a high retail value. Sometimes these decisions go beyond the market economics and are influenced by historical trading relationships. One example of this is the export of frozen lamb meat from New Zealand to the UK. Table 20 provides a comparison of energy use for different means of transporting freight.
Energy Use in Food Preparation
Table 3 indicates that the energy consumed by the household is the most significant in the 'food chain'. This will comprise contributions from shopping, storage and preparation.
Therefore, the householder is enabled, given accurate information, to make the choices which most determine the energy use connected with the consumption of food by the members of the household. There are many determinants in the energy contribution from food preparation, including choices of preparation method (eg grilling, frying, baking), fuel (gas, electric etc) as well as the foods to be prepared. One choice open to the householder is whether to use a gas or electric hob/oven. Data  does not imply a clear difference between the two methods. It would appear that electricity is a more efficient means to transfer heat to the foodstuff and the main losses are connected with generation efficiencies (44% from CCGT: see Table 25). Whilst the home combustion of gas may be less efficient there are lower losses prior to the fuel reaching the household as the fuel does not need conversion. From the data suggested by Pimentel & Pimentel, together with the efficiency of electricity conversion of gas in the UK, overall efficiencies for gas cooking of 37% (efficiency of transferring heat to product) and electric cooking of 33% (efficiency of conversion (44%) x efficiency of transferring heat to product (75%) may be deduced.