Last time I wrote about some of the basics involved with brewing espresso. Today I'll write a little about how roast degree affects the espresso. The darker the roast used for espresso, the more acidity, sweetness, and the coffee's natural flavor profile decreases and bitterness increases. So why would one use a very dark roast for espresso (also called a southern Italian roast)? Well, for one, the bitterness and carbony taste that often comes with a southern Italian roast cuts through milk better than a central Italian or northern Italian roast because it has more of a dark bitter punch than the other two (southern Italian roast contains more carbonized sugars while lighter roasts contain more caramelized sugars).
Using a darker roast for espresso also makes brewing a consistent shot much easier. Using a lighter roast provides one with the potential to brew a very rich, sweet, shot with lovely caramel flavor, and full of the coffee's natural flavors. However, the sugar structure of a lighter roast is easily damaged during brewing. This type of espresso can be ruined so many ways in brewing in handling that I won't get into it here. Blending beans for a northern Italian roast presents a challenge because the coffees one uses are more important than when blending for darker roasts because more of the actual coffee flavor and characteristics will come through in the northern and central Italian espressos. The largest concern when blending for a northern Italian espresso is that the blend should be low-acid when roasted to the proper degree. A Mocha / Java is widely considered to be the best blend for this roast, or, partially because Mocha and Java beans are quite pricy, a similar, less expensive blend of Ethiopian Harrar and Sumatra is often used. The balance of bitterness and the sweetness and varietal flavors lies further toward the bitter end in a central Italian roast than the Northern roast, but the coffee's varietal distinctions are still apparent.
For those who don't remember, I started this subject a couple issues ago because people mentioned that are espresso tasted different then what they have had previously. One of the primary reasons is because we use a central Italian roast while most espresso places will use a southern Italian or even darker roast. About a month ago, I talked to a roaster from Cleveland about why the large coffee chains use such a dark roast. I told him my theory; which was that 1) Because the USA drinks espresso-based beverages with much more milk on average than Europe, the large chains are ensuing that some bitter taste cuts through all that milk. and 2) Because of the quantity of labor the large chains need, it would be every difficult to train baristas to competently and efficiently handle the lighter roasts.
He politely told me that my theory was wrong and told me his. He believed that because of the huge quantity of beans needed by the chain, they are unable to be selective about the blends and bean quality of the coffee they need roasted, and therefore to achieve any satisfactory and consistent espresso, they need to roast to a southern Italian roast and even darker. He had a good point. But I'm a pretty stubborn person, so I'm going to say that there is probably truth two both of our arguments, and their decision to roast so dark was probably based on a combination of those reasons.