What happens to the bitterness of beer during fermentation?

During the fermentation process, the perception of bitterness in beer typically decreases. This is largely due to the yeast actively consuming some of the compounds that contribute to bitterness, specifically alpha acids. As yeast ferments the sugars in the wort, it also produces various byproducts, some of which can interact with bitter compounds, leading to a smoother and potentially less noticeable bitterness.

The decrease in bitterness can also be attributed to the dilution effect as carbonation occurs and the beer mixes during fermentation. Additionally, as the beer matures, the complexities of flavor can mask the bitterness, making it less pronounced in the final product.

The idea that bitterness decreases significantly highlights the biological and chemical changes that occur during fermentation, meaning that while the actual bitterness measured in International Bitterness Units (IBU) may not show a dramatic drop, the perceived bitterness by a consumer often does.