Beer and Carbon Dioxide

A good friend recently asked how much carbon dioxide is created by the brewing of a pint of beer. I’m not entirely sure I got the answer right, but if any science geeks would like to correct me, I’ll be glad to update my advice to him.

Here’s my attempt at answering, armed with only the Internet and my
misremembered chemistry classes from 1991.

Fermentation produces as many alcohol molecules as it does carbon
dioxide molecules. C6H12O6 -> 2(CH3CH2OH) + 2(CO2)
http://www.yobrew.co.uk/ferment.htm

Beer is typically 3-5% alcohol by weight (0.8 x ABV). I’ll take 4% as good enough for this example.
http://www.realbeer.com/library/beerbreak/archives/beerbreak20001005.php

A pint of water is about 473.176475 mL.
http://www.google.com/, search for “1 pint in mL”.

A liter of water weighs 1 kg.
http://www.mcps.k12.md.us/curriculum/science/instr/metricwater.htm

Therefore, a pint of water is about 473.176475 grams.

Therefore, a pint of beer (which is mostly water) contains about 4% of that, or 18.927059 grams of alcohol.

The molecular weight of alcohol is 46.069.
http://www.chemie.fu-berlin.de/cgi-bin/molform?CH3CH2OH

Therefore, a pint of beer contains about 18.927059 / 46.069 = 0.411
approx.) moles of alcohol.

The molecular weight of CO2 is 44.010.
http://www.chemie.fu-berlin.de/cgi-bin/molform?CO2

Therefore, 0.411 moles of CO2 contain 0.411 x 44.010 = 18.08811 grams of CO2.

Therefore, if all my other calculations and assumptions are reasonably correct, brewing one pint of beer should generate approximately 18.08811 grams of CO2.

Some of this will escape during brewing and some of it will end up in the beer, making it carbonated, escaping later in the form of fizz or burps.

And that concludes this episode of “Science by the Seat of your Pants”.

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