What is a common effect of stressing yeast during fermentation?

When yeast is stressed during fermentation, one common effect is an increase in the production of esters. Esters are aromatic compounds formed by the reaction between alcohols and organic acids during yeast metabolism, and they contribute distinctly fruity or floral aromas to beer. Stress factors may include excessive temperatures, lack of nutrients, or high osmotic pressure.

Under stress conditions, yeast often responds by producing more esters to facilitate its metabolic processes. This is thought to be a survival mechanism, as the production of esters can help to attract beneficial microorganisms to the environment, aiding with yeast health and fermentation efficiency.

On the other hand, the other choices focus on different aspects that are not typically associated with yeast stress. Increased attenuation refers to the yeast's ability to convert sugar to alcohol and carbon dioxide, and stressing yeast does not typically enhance this process. Lower alcohol content is indeed contrary to what might be expected, as stressed yeast often produces more alcohol rather than less. Lastly, rather than producing fewer phenolic flavors, stressed yeast can sometimes lead to an increase in off-flavors, including phenolic compounds if the stress is significant enough. Thus, the correct understanding of yeast behavior indicates that stress often results in heightened ester production.