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Beer science — the answers

bunsenandbeaker.jpgWe asked some of our brainy friends to answer a few questions about the science of beer. Tom was the first to respond. He’s a statistical genius, obsessed with lasers, and has studied science at Cambridge and Imperial College. His answers, with lots of disclaimers about how he’s not a chemist and wouldn’t want any of this to end up on the National Curriculum, are below.

1. Tom isn’t sure what to make of the idea that a huge head on your beer will cause the hop oils to migrate and ruin the flavour. He says:

Hop oils are volatile organic compounds, with the ‘volatile’ indicating that they like to evaporate. The evaporation of hop oils is not, however, necessarily a bad thing. Aroma being a component of flavour, you would be left with little from the hops other than bitterness if they did not do so.

I’m puzzled by the word ‘migrate’. To me this would suggest a slow process (perhaps diffusion of the hop oils along the boundaries of the cellular structure formed by the head) but this would then be impeded by the presence of a larger head. A more logical argument would seem to me to be that the hop oils diffuse into bubbles forming in the body of the beer, and that turbulence caused in careless pouring would lead to a large number of these forming at the beginning. Once these bubbles burst, the beer would have a lower level of hop oils than if the beer had been poured carefully, so affecting the flavour. The problem would then be not so much the presence of a large head than the *loss* of the head that negatively affects the flavour.

More generally, I would expect temperature to have a greater effect on the evaporation of hop oils, which is why it might be a good idea to drink beer a bit warmer, and yet another reason (if one were needed) not to go near Carling Extra Cold.

2. Tom thinks clear bottles are a bad idea.

This one I can believe, since many compounds are photoreactive. The breakdown of organic compounds by exposure to light sounds perfectly reasonable. Think of it as sunburn for beer.

3. Tom thinks beer with artificially added carbon dioxide might well taste different to naturally carbonated beer.

Interesting. Carbon dioxide, when dissolved in water, forms an equilibrium with carbonic acid (H2CO3) formed, if it is not obvious, from water and carbon dioxide. The equilibrium is formed slowly however, so artificially carbonated beer may contain higher levels of dissolved carbon dioxide and lower carbonic acid than the equilibrium, so depending how soon after carbonation the beer was drunk it may have a lower acidity than beer with naturally produced carbon dioxide.

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