What does "percolation" refer to in coffee brewing?

Percolation in coffee brewing refers specifically to the method of brewing coffee by cycling boiling water through coffee grounds. This technique involves repeatedly passing hot water through the coffee grounds, allowing for a thorough extraction of flavors, oils, and compounds from the grounds.

In a percolator, water is heated to a boil and then forced up a tube to the coffee chamber where it saturates the grounds. As the water passes through the coffee, it absorbs flavors before it drips back down into the reservoir, and the cycle repeats until the desired strength is achieved. This method can produce a strong and rich brew, as the continuous cycle allows for maximum extraction.

The other options describe different aspects of coffee preparation but do not accurately reflect the process of percolation. For example, infusing coffee grounds with hot water refers more broadly to brewing methods, and combining espresso with frothed milk describes a specific technique related to cappuccinos or lattes, while filtering coffee pertains to the removal of solids rather than the brewing process itself.