Which off flavor is commonly associated with over-sparging during brewing?

The off flavor commonly associated with over-sparging during brewing is astringency. Over-sparging occurs when too much water is used to rinse the grain bed, potentially extracting undesirable compounds, especially tannins, from the grain husks. These tannins can lead to a drying, puckering sensation on the palate, which is characterized as astringency.

In the context of brewing, a certain balance between extraction and sweetness is critical. When over-sparging happens, the sweet flavors from the malt can become diluted, and the increased extraction of tannins disrupts the desired flavor profile, introducing an unwelcome astringent taste that detracts from the overall enjoyment of the beer.

The other options, while they represent off flavors that can occur in beer, do not directly correlate with the process of over-sparging. Diacetyl is primarily a by-product of yeast metabolism, often resulting from under-attenuation or poor yeast health, and oxidized flavors stem from exposure to oxygen during the brewing or storage process. Esters, fruity flavors produced during fermentation, are typically related to yeast characteristics and fermentation conditions rather than the sparging process.