Environmental Engineering Reference
In-Depth Information
juice about 20 MJ/kg, fruit and vegetable canning about
5 MJ/kg, and oil pressing 10-15 MJ/kg.
The energy cost of bread was first traced by Johnson
and Hoover (1977), who analyzed the sponge-dough
process. The cost of 7.3 MJ/kg of white bread at retail
was divided 2:1 between production and delivery to
stores. Baking claimed only about 17% of all energy,
most of it for water evaporation. Beech's (1980) audit
of three English bakeries yielded 6.43-7.14 MJ/kg with
direct energy use being 70%-80% of the total, packaging
about 12%. Beech (1980) found striking economies of
scale for home baking (three breads in oven costing
about 50% less per kilogram than a single bought loaf )
and a cost only slightly higher (7.8 MJ/kg) than in com-
mercial operations. Adding the energy cost of wheat-
growing (4-7 MJ/kg) and grain-milling (at least 2 MJ/
kg) raises the overall cost to 14-17 MJ/kg, a compara-
tively modest subsidy to produce 10.6 MJ/kg of food
energy with at least 8% of incomplete (lysine-deficient)
protein. Assorted pastry products can embody much
more energy, fruit pies as much as 35 MJ/kg (Biesot
and Moll 1995).
Food packaging is fairly energy-intensive, especially
with the use of plastics and aluminum and the inclusion
of waste disposal costs. Modern retailing is energized
largely by electricity; about 60% of its energy use is asso-
ciated with refrigeration; lighting and space heating/
cooling take about 15% each. Total energy needs vary
mostly between 400 W/m
2
and 450 W/m
2
of selling
area, and a bakery and deli section can increase the rate
by up to 50%. Cooking is a rather inefficient heat transfer
even in modern kitchens; its annual needs range from 3
GJ to 5 GJ per household. Throughout the poor world
cooking with traditional stoves wastes most of the energy
in wood or crop residues, but more efficient kerosene
stoves are risky to use.
Microwavable foods and higher shares of meals eaten
away from home have increased the demand for refriger-
ation. Home refrigerators were marketed first by Kelvina-
tor Company in 1914, and freezers were introduced in
1940. The early models rated about 200 W/m
3
, the first
frost-free refrigerators needed about 350 W/m
3
, and
models with large freezer sections consume up to 450
W/m
3
. Freezers require 18-23 MJ/kg of load. The
popularity of fast food has increased demand for refriger-
ation, which now consumes 5%-10% of electricity in rich
nations. Fortunately, better refrigerator designs offer sub-
stantial electricity savings. The energy cost of cut flowers
put on a dining table can be 1 OM higher than that of
common foodstuffs. A detailed Dutch study put the aver-
age energy cost at about 9 MJ/flower, ranging from
more than 50 MJ/stem for a flamingo flower to 3 MJ/
stem for a sword lily, with tulips at 4 MJ/stem, carna-
tions at about 5 MJ/stem, and roses at almost 10 MJ/
stem (Vringer and Blok 2000). When adjusted for life-
time optimal conditions, common lilies and carnations
(400-500 kJ/stem per day) are the least demanding.
