What is the effect of grinding coffee too coarsely?

Grinding coffee too coarsely results in under-extraction, which explains why this choice is the correct one. When coffee is ground coarsely, the surface area exposed to water is reduced, leading to a situation where water cannot efficiently extract the flavors and oils from the coffee grounds. This insufficient extraction leads to a brew that often tastes weak or watery, lacking the depth and complexity one would expect from properly brewed coffee.

In contrast, finer grinds have a larger surface area, promoting better extraction of the desirable flavors, oils, and caffeine from the coffee. If the coffee is ground too coarse, despite the brewing time, the water may not reach the right balance of flavors and strengths, resulting in a disappointing cup.