Can someone explain to me the science behind fusels?

[thechemister]

Any biologists or chemists know why a higher temperature can cause fusels?

It's confusing to me that by simply raising the temperature of the fermentation can change the actual molecular structure and chemical composition of the products. I can't seem to find anything from a basic google search.

Also are different fusels associated with beer as opposed to wine or mead?

 

[andhou27]

High temperatures cause reactions to progess faster, due to an increase in particle movement and energy. An increase in energy could help to bind alcohol components into fusel alcohols. Also an increase in temperature causes yeast to convert sugar into alcohol faster. This increases the population of yeast very quickly, leading to over crowding and increased competition. Overcrowding can stress the yeast, causing die off and leading to fusel alcohols. Fusel alcohols are by products of any distillation, so whatever you are fermenting can contain them. The goal is to control the speed of fermentation by allowing the yeast to work slowly and not become stressed by the environment.

 

[thechemister]

Ah, I think I see. I knew yeast could be stressed by being under pitched, but I didn't know over crowding did it as well. So are fusels generally just longer chains of alcohols?

 

[AlCophile]

Folks:
Search HBT for the Chemistry of Beer online course starting this Jan 13, from U of Oklahoma, and sign up. Also, see Amazon for BrewChem 101.

 

[andhou27]

Fusels are multiple different alcohols that are fused together and happen to either smell or taste bad.

 

[indianaroller]

Ah, I think I see. I knew yeast could be stressed by being under pitched, but I didn't know over crowding did it as well. So are fusels generally just longer chains of alcohols?

Fusel or higher alcohols are produced in the early stages of fermentation. Lots of oxygen and heat at the start of fermentation could increase fusels.

 

[g-star]

Fusels are multiple different alcohols that are fused together and happen to either smell or taste bad.

This is not exactly correct. Fusel alcohols are 3-5 carbon alcohols, mainly n-propanol, isobutanol, and isoamyl alcohol. For reference, ethanol is a 2-carbon alcohol.

Fusels are formed under conditions of elevated temperature and thus fermentation kinetics through a catabolic or anabolic pathway, and are derived from either amino acids or amino acid synthesis.

This paper has some good background info: http://goo.gl/vb0f3K