Why is it beneficial to raise fermentation temperature at the end of the yeast's high growth phase?

Raising the fermentation temperature at the end of the yeast's high growth phase is beneficial because it encourages yeast to clean up byproducts such as acetaldehyde and diacetyl. During fermentations, yeast not only converts sugars into alcohol and carbon dioxide but also produces some unwanted byproducts that can impact the flavor and aroma of the finished beer.

Acetaldehyde is a compound that can impart a green apple-like flavor, while diacetyl can create a buttery taste that is undesirable in many beer styles. By increasing the fermentation temperature, yeast metabolism is stimulated, which helps to promote the reabsorption and further conversion of these off-flavors into less noticeable compounds. This process contributes to a smoother and cleaner finished product.

In contrast, the other choices, while having their own merits in specific contexts, do not directly address the primary goal of raising the temperature at this particular stage of fermentation. For instance, while enhancing yeast survival rate can be a valid consideration, the cleanup of unwanted compounds is generally prioritized for improving beer quality. Similarly, flavor enhancements and carbonation processes can be influenced by various factors throughout fermentation but are not the immediate focus of a temperature increase at this specific point.