Adam's recommendation: There is also an excellent supplement to this book from Scott (only available as a Kindle e-book) that goes further in-depth into espresso extraction mechanics and behaviour - linked here.
About the Author
Scott Rao started his first cafe & roastery in Amherst, MA when he was 22. That first cafe quickly became an institution, serving well over 1000 customers per day and tripling the sales volume of the Starbucks down the street. After selling his first cafe, Scott went on to work in the New Zealand coffee industry. He then returned to the US to open a restaurant and coffee roastery inspired by his travels down under. Scott later founded a pioneering cafe in Montreal that influenced coffee making worldwide.
Upon selling his second business, Scott began writing books about coffee making in the hopes of helping roasters and baristas become more educated and systematic in their approach to coffee. Scott parlayed those books into a consulting career and now spends his time consulting for coffee roasters around the world, teaching the world's most advanced roasting masterclasses, and designing next-generation coffee equipment.
Scott secretly likes Sencha tea more than coffee, is baffled about why anyone drinks naturals, and would probably do a free consulting job for you if your business happens to be located on a warm surf beach.