What causes the apple acetaldehyde aroma in green beer?

The presence of apple-like acetaldehyde aroma in green beer is primarily due to insufficient fermentation time. During fermentation, yeast converts sugars into alcohol and other byproducts, including acetaldehyde. This compound is a natural intermediate that the yeast will typically convert to ethanol as fermentation continues. If the fermentation process is cut short, or if the yeast is underactive, acetaldehyde can accumulate, leading to noticeable off-flavors such as green apple.

Other factors such as excessive hops, over boiling of the wort, or improper storage may affect the beer’s overall profile but do not directly cause the formation of acetaldehyde. For example, excessive hops can contribute bitterness or aroma but are not associated with generating acetaldehyde. Over boiling can lead to caramelization and darkening of the wort but does not relate to fermentation byproducts. Improper storage conditions may spoil the beer but would not specifically increase acetaldehyde levels unless related to yeast performance during fermentation. Understanding the fermentation process in depth highlights why sufficient fermentation time is crucial to prevent the buildup of undesired compounds like acetaldehyde.