What is a potential source of tannins in beer?

Tannins in beer are primarily phenolic compounds that can contribute to astringency and flavor complexity. One of the most notable sources of tannins in beer is the malt during the milling process. When malt is ground finely, the cell walls of the grains are broken down more effectively, which can lead to the extraction of polyphenols and tannins during the mashing and boiling stages of brewing. These tannins can come from the husks of the grains, which tend to release more tannins when over-milled. Therefore, over-milling malt can significantly increase the potential for tannin extraction, impacting the final flavor and mouthfeel of the beer.

On the other hand, insufficient yeast pitching, excessive fermentation temperature, and low hopping rates do not have a direct impact on tannin levels. Insufficient yeast pitching is more likely to lead to fermentation issues and off-flavors due to stressed yeast, while excessive fermentation temperatures can cause unwanted esters and phenols but do not contribute to tannin content. Low hopping rates, meanwhile, are related to bitterness and hop aroma but have little to do with tannin extraction from malt.