Which alpha acid is associated with the isomerization process during the brewing boil?

Humulone is indeed the alpha acid primarily associated with the isomerization process that occurs during the brewing boil. When hops are boiled during the brewing process, the heat causes the humulone molecules present in the hops to undergo isomerization. This chemical transformation changes their structure, leading to the formation of iso-alpha acids, which are responsible for the bitterness in beer.

The significance of this transformation is that iso-alpha acids are more soluble in water, making them effective in contributing to the overall bitterness profile of the beer. This process is critical in balancing the sweetness of the malt with the bitterness of the hops, resulting in the final flavor profile of the beer.

Other choices like myrcene, beta acids, and polyphenols do not undergo this specific isomerization process during boiling in the same manner nor produce the iso-alpha acids that directly contribute to beer bitterness. Myrcene is a volatile oil contributing to hop aroma, beta acids do not isomerize and contribute less to bitterness, while polyphenols mainly affect mouthfeel and stability rather than bitterness. Thus, humulone is clearly the alpha acid most directly linked to the isomerization process during brewing.