While sitting back drinking a pint, I got to wondering. My beer comes in a standardized bottle of 351 millilitres. According to charts, it contains about 145 kCal or energy. This is 6.1e5 joules (0.61 MJ) of energy.
Going through my trusty brewers book, I can make a nice stout using;
- malted barley
- pearled barley
- roasted barely
- gypsum
- hops
- irish moss
- ale yeast, and
- corn sugar
After all sorts of processing, this recipe delivers 5 gallons!
What’s the energy requirement? Well barley yields about 3 570 kg/ha, so I need a crop from approximately 11.1 square metres. Hops provide 3 kilograms per hectare, thus requiring about 0.567 square metres. Sugar cane comes in at 65 tons per hectare, so about 0.077 square metres of land are needed for this. I’m going to assume the remaining ingredients are ready at hand and require minimal effort.
The Sun shines down at 1387 watts per square metre of which about a half reaches land. Where I live, the annual sunshine is 2000 hours a year. Given a crop takes one year then I assume that all the sun’s energy is dedicated to the crop. Hence, assuming the Sun is always at nadir, the 12 square metres soaks up 6e10 joules (60 GJ) of energy from the Sun.
I need about 2.4e6 joules of energy to heat water for extracting the necessary flavours.
Hence, in comparing the energy in the beer of 6.1e5 joules to the energy deposited by the Sun of 6e9joules, the energy ratio is about 10000:1 or about 10 000 joules of energy from the Sun are needed to make 1 joule of energy in the beer. Interesting.
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