Global ChangeIntersection of Nature and Culture

How much energy to make a meal?

Friday, February 12th, 2010

Science Magazine (subscription required) is running a special issue this week on food security.  There are so many articles, it’s hard to know where to start.

Let’s go with an interesting, visible example from a news article showing that different meals can require vastly different amounts of energy to make (click on this link for a nice downloadable color figure).

(1) Beans: Amount of energy needed to grow, package, transport, and cook (what I assume to be one serving) in Sweden.  Note, a megajoule is one million joules, or about 240 dietary calories—the amount of energy in almost 2 cans of soda:

• Brown beans (8.9 megajoules, 2,127 dietary calories)
• Yellow peas (5 megajoules, 1,195 dietary calories)
• Imported soybeans (7.9 megajoules, 1888 dietary calories)
• Imported brown beans (11 megajoules, 2,629 dietary calories)
• Imported canned beans (20 megajoules, 4,780 dietary calories)

Bottom line: Commercial canning is energy intensive and food miles matter.

(2) A single meat-based dinner

Amounts of energy to grow, package, transport, and cook each meal:

• Dinner 1 (19 megajoules, 4541 dietary calories to make)
  • Beef (9.4)
  • Rice (1.1)
  • Greenhouse tomatoes (4.6)
  • Wine (4.2)
• Dinner 2 (6.1 megajoules, 1457 dietary calories to make)
  • Chicken (4.37)
  • Potatoes (0.91)
  • Carrots (0.5)
  • Cooking oil (0.3)
  • Tap water (0)

Both of these dinners yielded about the same dietary energy to the eater:

• Dinner 1: 2.52 megajoules, 602 dietary calories
• Dinner 2: 2.60 megajoules, 621 dietary calories

This means that dinner 1 yields about 13% of the energy required to make it, whereas dinner 2 yields about 43%.

Bottom line: It takes three times more energy to make dinner 1 than dinner 2.  More energy use with conventional agriculture means more fossil fuel use and more climate warming.

Science 327: 809  DOI: 10.1126/science.327.5967.809

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Photo credit: http://www.flickr.com/photos/bludgeoner86/ / CC BY 2.0