What is a potential downside of a protein rest that lasts longer than 30 minutes when using well-modified malt?

A protein rest, typically done during mashing, aims to break down proteins in the malt, particularly those that can lead to haze in the finished beer. When using well-modified malt, the grains are already efficiently processed, and extended protein rests beyond 30 minutes can lead to the breakdown of proteins that contribute to body and foam stability in the beer.

When the protein complex is overly diminished, the resulting beer can have a thinner mouthfeel and reduced head retention, as the proteins that help stabilize foam and contribute to body are no longer present in adequate quantities. Therefore, the correct answer highlights the risk associated with longer protein rests, particularly when using malts that are well-modified.

The other options touch on different aspects of the brewing process but are not directly related to the consequences of an extended protein rest for well-modified malts. Increased bitterness, decreased fermentation activity, and elevated alcohol content are not typically influenced by the duration of a protein rest but are more related to other factors in the brewing process, such as hop additions, yeast health, and fermentation conditions.