We all look for sweetness in the cup and something we often ignore is how we cool the coffee after we roast it. But, it is part of the process. I don't like water quenching, but I am a proponent of trying to cool the coffee once it comes out of the roaster in four minutes or less
. And why do I say that? We've done experiments using exactly the same strategy cooling the coffee in six minutes, five minutes, and four minutes. From six minutes to five minutes there is a small improvement in the sweetness of the coffee. When you go from five minutes to four minutes, the sweetness in the cup doubles and there is a definite chemical explanation for why that happens
. This is due to sugar solubility. The primary sugar in coffee is sucrose. During the roasting process you fracture the sucrose and you want to caramelize it or polymerize it in the scientific term. But, you also have to maintain solubility. If it doesn't come out when you put water into it, it is not going to be a sweet cup. Having the sugar there is one issue, being able to get it out with hot water is another issue. If you cool it too slowly, the long series chain polymers, sugars, fructose and glucose will find other constituents to link up with in the coffee and they are not as soluble.
Likewise, during the roasting process if you form molecules that are very large, they may be favorable for espresso extraction you will get a lot of crema. Having the starches, oils, lipids, and fatty proteins in the coffee is a very good thing for espresso. But, when you try to apply that same strategy to coffee that is going through a paper filter, the water doesn't want to go through the filter. The larger molecules get trapped by the paper filter and don't end up in the cup.