Simply put, when coffee bean roasting enters second crack, it is called dark roast; from dense first crack to before second crack, it is called light roast to medium-dark roast, and the color also approaches black as the roast gets darker.

First, let's talk about dark roast. When it comes to dark roast, one must mention the coffee world's legendary figure Alfred Peet. In the 1960s, Mr. Peet devoted himself to promoting heavy-roast coffee (dark roast), because at that time roasters, in order to reduce costs, roasted coffee beans only until first crack was in progress. At this point, the weight lost by the coffee beans due to roasting was about 10-15%, still 10% less than heavy roasting, meaning that in order to lower costs by one tenth, they did not care about selling coffee beans with underdeveloped flavor to consumers (this does not mean light roast is bad, but refers to behavior that disregards flavor solely to cut costs).

Alfred Peet
 
After World War II, American coffee consumption jumped year by year. At the time, roasters, in order to expand profits, roasted lighter and lighter. First, this could save labor time and fuel costs; second, it could reduce the weight-loss ratio of roasted beans. At that time, coffee beans were rushed out of the roaster just as first crack had only begun, with a weight-loss ratio of less than 9%; compared with dark-roasted beans released after second crack, whose weight-loss ratio was as high as 18%, light-roasted beans yielded at least one tenth more profit than dark-roasted beans. This was the light-roast money-making trick commonly used by unscrupulous operators in the early days, and they even went further by blending in large amounts of coarse natural-process beans. One can imagine how bad the coffee tasted then; no wonder it was ridiculed as "dishwater coffee." But consumers had long been accustomed to half-raw, sour, astringent, bitter coffee. To make it smoother, they had no choice but to add more water to dilute it, so thin, watery coffee became the popular taste of the time. As long as there was caffeine for alertness, it did not matter whether the coffee resembled sour, foul swill. This must be blamed on the U.S. military, which during the war, for convenience of storage, rationed coffee to frontline officers and soldiers that was either extremely light-roasted or instant. After these people retired and entered society, they naturally brought the overly diluted, weak coffee taste into the workplace. In the one or two decades after the war, major American roasting companies Folgers and Hills Bros vigorously promoted extremely light-roasted large-can coffee beans (grounds). Over time, the public did not know what fresh coffee was and had grown used to stale coffee, which still tasted good if one desperately added sugar and creamer. The flood of bad coffee was a postwar aftereffect, and this phenomenon also existed in Europe, because the public was fully devoted to reconstruction and had little room to discuss food and drink. This was the reason the American roasting industry at the time only sought to sit back and enjoy huge profits, lacking the moral courage to denounce this disguised light-roast "money-grabbing" trend.

Therefore, in 1966 Mr. Peet opened Peet's Coffee & Tea in San Francisco on the U.S. West Coast, insisting on using 100% Arabica beans and absolutely refusing to sell coffee beans roasted before second crack. If dark-roasted beans are roasted and brewed correctly, they can yield excellent coffee that is quite sweet, richly flavored, and full-bodied, completely different from the bitter, astringent coffee in most people's impressions. "Peet's Coffee" disdained the most popular half-raw light-roasted beans of the time and instead took the deep roast route. Whether single-origin or blends, all were roasted until the middle-to-late second crack before being released, and it switched to using harder Arabica beans that could withstand longer roasting in its formulations. That is to say, at "Peet's Coffee" you absolutely could not drink light-roasted beans from before second crack or Robusta beans.

Mr. Peet also taught everyone the correct brewing method. He brewed at twice the concentration of the weak coffee prevalent at the time, that is, using 30 grams of freshly ground coffee powder and a French press to brew 360 cc of coffee, breaking the old bad habit of using 10-15 grams to brew 360 cc of weak coffee. Most people drinking "Peet's Coffee" for the first time would blurt out: "Wow, are you trying to poison me? So strong!" Later, after the coffee "blossomed and released fragrance" in the mouth and they underwent a shocking education for the taste buds, they changed their tune one after another: "Wow, strong in a satisfying way, pungent in a great way, sweet enough to soothe the throat!" Those who knew quality were mostly European immigrants in the early days, finally finding in America coffee like fine nectar and jade. Interestingly, unwashed, smelly hippies liked to gather at "Peet's Coffee," sitting or lying down, as if coming here to receive a fragrant smoke bath from dark-roasted beans. Hippies hanging around the shop in groups was a major feature of "Peet's Coffee." Although the shop combined stench and fragrance, everyone who walked into "Peet's Coffee" could not help taking a deep breath to experience a world of strange odors in which fragrance exists within stench and stench within fragrance, including the burnt aroma, wine aroma, coffee essential oil aroma, and banana oil aroma unique to dark-roasted beans, as well as the unique smelly sock odor and body odor of hippies. It could truly be called a blending of fragrance and stench, a mixture of a hundred smells!

Later, Starbucks founders Jerry Baldwin, Gordon Bowker, and Zev Sieg also decided to open a coffee shop because they fell in love with Mr. Peet's coffee, and at first they even received Peet's assistance. Not only did Peet provide coffee beans roasted by Peet for Starbucks to sell, but even the initial shop furnishings were similar to Peet's Coffee. It can also be said that without the early Peet, there would be no present-day Starbucks. Now everyone knows Mr. Peet's major influence on you and me!!! Here we offer the highest respect to Mr. Peet for his contributions to coffee!!! 
 
Now let's talk about light roast. Then we must also mention George Howell. He lived in San Francisco from 1968 to 1974 and became infatuated with Peet's coffee during that time. Later Howell moved to Boston, but could not find fresh roasted coffee similar to Peet's. Since he could not buy it, he would sell it himself, so in 1975 he founded Coffee Connection.

George Howell

But after all, a legend is a legend. Peet's heavy-roasting technique was not so easy to imitate (it is said to be related to Peet's self-modified roaster). Therefore, in frustration, Howell went the opposite way and adopted light roasting. Unexpectedly, under "correct" technique, the bright fruity acidity of light-roasted coffee beans was quite charming, and flavor differences among beans from different origins were obvious. From then on, Howell adopted light roasting, which became widely popular on the U.S. East Coast, standing in opposition to Peet's heavy roasting on the U.S. West Coast.

(Later Coffee Connection was acquired by Starbucks, and within two years all stores were under the Starbucks signboard; the original consistent light roast was also changed to Starbucks' signature dark roast.)