AskPablo: CO2 from Beer

duff.jpgHave you ever wondered about the carbon emissions generated from making your favorite brewsky, bottle of vino, or 15 year-old Talisker Scotch? Never mind the impact from producing the bottles, shipping the product, or the farm impact–I’ve written about those before (See: AskPablo: Exotic Bottled Water, AskPablo: Glass vs. PET Bottles, and AskPablo: Foodmiles) But what about the fermentation process? That is what we will explore this week on AskPablo.


Alcohol is the result of a fermentation process in which sugars are eaten by small yeast critters which then metabolize it, pee alcohol, and fart CO2. No, it doesn’t sound too appetizing, but it’s the truth…The amount of alcohol depends on the amount of sugar available. In beverages that contain higher levels of alcohol, some of the water has been removed through distillation. So, if your drink of choice is Scotch, Vodka, or Gin, you can add some more CO2 emissions from the operation of the distillery. Of course, distilled alcohol is more concentrated, which means less packaging and less shipping emissions per unit of beverage when compared to beer or wine.
Sugar content in the original, unfermented batch is measured in units called “brix.” Brix is a ratio between the weight of the sucrose (sugar) in the solution and the weight of the solution itself. So 10 g of sucrose in 100 g of solution would have a brix value of 10. There is a direct correlation between brix and specific gravity, which is more commonly used in brewing. Beer is typically between 5 and 15 brix, depending on the desired final alcohol content. Grape juice used in wine making is between 22 and 30 brix. The reason brix is important to us is that it tells us how many grams of sugar are going to be converted into alcohol and CO2 per 100 grams of solution.
Let’s say that our favorite brew has a brix of 12, or 12 g of sucrose per 100 g of solution. We can ignore the water, which is 88% of the solution. The glucose molecule (C6H12O6) has a molecular weight of 180.16 g/mol and, when metabolized by the yeast, becomes 2 ethanol molecules (CH3CH2OH) and 2 carbon dioxide molecules (CO2). A CO2 molecule has a molecular weight of 44.0095 g/mol. So the conversion ratio between the sugar and the CO2 is 48.8% ((44×2)/180). This means that the amount of sugar (12 g) times the conversion ratio (48.8%) equals the amount of CO2 produced per 100 g of solution. In this case it comes out to 5.856 g of CO2.
Keep in mind that this CO2 production actually reduces the amount of the solution. So, per final 100 g of beer, we need to create 6.22 g of CO2 (5.856/(100-5.856)x100). This is 62.2 g of CO2 per liter of beer. Maybe this doesn’t sound like much, but let me put it in perspective: in 2004, Americans drank 23.974 billion liters of beer, resulting in 1,491,182 mT of CO2 emissions. Global beer consumption in 2004 was 150.392 billion liters, resulting in 9,354,382 mT of CO2 emissions. For a little something more to think about, the US emitted a total of 1,446,777,000 mT of CO2 in 1996. Now, keep in mind that this is based on an assumption of a brix value of 12. The average beer may be a bit weaker than that. Feel free to plug in your own assumptions to see what you get. Either way, the CO2 emissions from brewing are not negligible. We probably haven’t heard much about it since it is the result of a natural process and not the burning of a fossil fuel. But CO2 is CO2…
Cheers!
Pablo Päster, MBA
Sustainability Engineer