It seems like many people are confused about what espresso is. Is it a roast? Does it have to be dark? Do I need an espresso machine to enjoy it? The answer to all of those questions are 'no'...or at least, not necessarily.
Espresso, while famously Italian, was invented in France in the late 1800s. Espresso was commercialized in 1903, starting with Luigi Bezzera's patent of a "Coffee Making Machine." The original goal of espresso was not to make a concentrated coffee beverage, rather the purpose was to brew a cup quickly. These machines in the late 1800's and early 1900's used steam pressure to force boiling water through a small portable metal filter filled with fine coffee. If you saw this today, it wouldn't remind you of a classic doppio espresso in the slightest.
Modern espresso was invented in the 1940's by Achille Gaggia, who found that if the coffee was brewed between
195-205 degrees Fahrenheit and at a pressure of 9-10 bars (130-145 psi), something extremely cool would happen. He discovered that the gasses released from the coffee would turn into really small bubbles, and sit on top of the espresso as a foam. This is what he called cafe crema, and it became the new standard when making espresso. This is typically seen as a sign of freshness if a shot of espresso has a lot of crema because there are more gasses in coffee when it is freshly roasted.
Fun Fact: If you order an espresso at a coffee shop, it will most likely be served with a small spoon. This is traditionally used to stir the espresso and the crema together to create a more balanced drink, because the crema is very sour by itself.
So what does all that mean for you?
Notice throughout that history lesson, there was no mention of roast level. That is because the coffee used in an espresso machine is typically a blend of coffees that the roaster thinks tastes good in a concentrated form. However, it does not need to be dark. Espresso blends tend to be roasted darker so the flavors are more prominent in milk, but you can really use any coffee as an espresso. Also, it is worth mentioning that if you pick up an "Espresso Blend" from us, or any other roaster, you can make it on a pour over, french press, etc... and it can still taste great! Don't limit yourself.