Which substance is responsible for the yellowish or brownish bitter taste in bourbon?

The yellowish or brownish bitter taste in bourbon can be attributed to tannins. Tannins are polyphenolic compounds found in the wood of the barrels used for aging bourbon, particularly in charred oak. During the aging process, bourbon interacts with the wood, extracting tannins, which contribute to the flavor profile. These compounds can impart astringent and bitter notes, enhancing the complexity of the bourbon's taste.

Tannins play a significant role in the sensory experience of bourbon, balancing sweetness from the sugars in the grains and caramelization from the charring process. This interaction not only influences the taste but also the overall mouthfeel, adding to the richness and depth commonly associated with high-quality bourbons.

While other options, such as yeast and caramel color, contribute to the overall character and appearance of bourbon, they do not specifically relate to the bitter flavor associated with tannins derived from barrel aging.