Which type of fermentation condition can hinder the ester production in brewing?

Under aeration during fermentation can indeed hinder ester production in brewing. When yeast is exposed to excessive oxygen, it tends to focus on producing compounds that are more associated with aerobic metabolism rather than anaerobic fermentation. This shift in metabolic focus leads to a decrease in the production of esters, which are important for adding desirable fruity and floral aromas to the beer.

Esters are primarily produced during the fermentation process when yeast ferments sugars under anaerobic conditions. Yeast produces esters as a result of the combination of alcohols and organic acids in a low-oxygen environment. Therefore, if the fermentation environment is altered by the presence of too much oxygen, it diminishes the conditions necessary for ester synthesis, resulting in a beer that may lack the complex aromas typically sought after in many styles.

Low temperature pitching, under pitching yeast, and fermenting at high gravity can all influence ester production in different ways, but they do not directly affect the oxygen availability in the same manner that under aeration does. For instance, low temperatures might reduce yeast activity and ester formation, but they do not inhibit the fundamental biochemical pathways for ester production as directly as over aeration does.