### Introduction Added from page *x* on [[2026-03-27|2026-03-27 15:26]]: > This book will focus on the physics of filter coffee brewing, with particular attention to manual percolation methods such as pourovers. This is the first angle from which I began exploring the concepts underlying coffee extraction, simply because this turned out to be my favorite brew method. ^p0000-001 --- ### Extraction #### Average Extraction Yield Added from page 2 on [[2026-03-27|2026-03-27 15:33]]: > Putting the concepts of average extraction yield and coffee concentration together, Earl E. Lockhart created the Coffee Brewing Control Chart in the 1950s at the Coffee Brewing Institute. ^p0002-001 --- Added from page 3 on [[2026-03-27|2026-03-27 15:34]]: > Average extraction yields below 18% were deemed underextracted and associated with less-pleasant flavors such as grass and peanuts, and those overexatracted above 22% were associated with bitterness and astringency. Since these early developments, it has become clearer that the optimum average extraction yield is significantly impacted by factors such as roasting (Rao 2014), grinder performance (Rao 2018), brewing methods, and green coffee quality, as well as personal preference. We will explore these effects in more details in the following chapters of this book, but it is useful to keep in mind that recent developments in roasting, farming, and grinder quality have led the typical range of preferred average extraction yields to shift slightly toward higher values. ^p0003-001 --- Added from page 3 on [[2026-03-27|2026-03-27 15:37]]: > The optimum zone in coffee concentration is correlated with flavor intensity rather than the flavor profile, and as such there is a much wider range of preferences. The Coffee Brewing Institute found an acceptable range between 1.0% and 1.5%, but the lower end of this range is now more rarely encountered in the specialty coffee community. These preferences are, in principle, independent of those in average extraction yield. They are simply based on how strong we like our coffee to taste. ^p0003-002 --- Added from page 4 on [[2026-03-27|2026-03-27 15:39]]: > a cup of coffee with an average extraction yield above 28% would include almost every dissolvable compound that the coffee bean contains. Typically, this is not a good thing because some of the slower-extracting compounds can taste harsh, bitter, and/ or metallic and cause an astringent sensation on the tongue. Conversely, a cottee extracted at around 15% would exclude a lot of the interesting compounds and would likely lack sweetness and complexity. ^p0004-001 --- #### Advection and Diffusion Added from page 5 on [[2026-03-27|2026-03-27 15:44]]: > Advection is the technical term for simply transporting a compound with the flow of water. ^p0005-001 --- Added from page 5 on [[2026-03-27|2026-03-27 15:45]]: > Diffusion describes how a chemical compound will distribute itself, even in the absence of flow. ^p0005-002 --- Added from page 6 on [[2026-03-27|2026-03-27 15:47]]: > Therefore, the process of coffee extraction takes place in two distinct steps: a slow process of diffusion that brings chemicals from the core to the surface of the coffee parti-cles, and a fast process of advection once they reach the surface. ^p0006-001 --- #### Particle Size