There are a variety of things to consider when buying coffee including the characteristics of the different types of coffee, the equipment you'll be using to make the coffee, and how you'll be drinking it. Because different types of coffee beans have specific tastes, aromas, and levels of acidity, knowing a little bit about major bean varieties can be helpful. Additionally, you should look at how the coffee is processed and stored, as well as how fresh it is.
Types of Beans
Most coffees are made with at least one of three types of beans: arabica, robusta, or kona. Though each of these types has specific tastes and smells associated with it, they can perform differently depending on the roast or method of preparation. Arabica beans are the most commonly used, and generally make mild, aromatic coffees. Many South American coffees are made with arabica beans, but they're also found in Indonesian and Kenyan coffees.
Robusta beans generally have more caffeine than arabica beans, but they also are more bitter. This means that they're often used to give strength to arabica blends, or to make instant coffees. Kona beans are often considered the best coffee beans in the world, and are much rarer than either arabica or robusta beans. They are exceptionally low in acidity, and often have a nutty taste. Since they're of such high quality, they're usually very expensive.
The main characteristics you should consider in a coffee are its roast, acidity, aroma, body, and balance. The roast of a coffee is determined by how hot the insides of the beans get during the roasting process. Light roasts tend to let the most of the original bean's characteristics through, but this can make the bean taste too intense or unbalanced. Medium roasts have more of a caramelized, sometimes acidic taste, but usually don't have the chocolatey taste that many dark roasts have. Dark roasts are typically the most caramelized, but can taste too burned for some drinkers. Different types of beans will taste differently than others of the same roast, though, so its worth experimenting.
Another factor to take into consideration is the coffee's acidity. Light roasts tend to be the most acidic, but a coffee's acidity can also vary depending on the type of beans it includes and where they were grown. For instance, Kenyan coffees tend to have a higher acidity than Haitian coffees. It's also important to consider the aroma of the coffee, which is how it smells after being ground and brewed. The aroma can be rich and full, as in the case of Colombian coffee, or spicy, as with some Sumatran coffees.
Additionally, it's important to consider the body and balance of the coffee. The body is how it feels in your mouth as you drink it, while the balance is how all the flavors interact. Coffee can be light, medium, or full-bodied, depending on the roast and how the coffee is prepared. Most coffees are at their most balanced with a medium roast, but it can be interesting to drink unbalanced coffees as well. For instance, some people prefer very acidic coffee, or coffee with a strong ashy flavor.
Processing and Storage
How a coffee is processed and stored is very important in terms of determining its quality. It's generally best to buy loose coffee beans, but only if they are stored in airtight bins that are regularly refreshed. Whole beans tend to hold onto their flavor and aroma much longer than ground beans, but freshly ground beans can also be of high quality, particularly if they're sold very shortly after being roasted. When buying coffee that comes in presealed bag, you should gently squeeze the bag and smell the air that comes out of the valve to get a sense of its aroma.
What kind of equipment you will be using to make the coffee also plays a role in choosing the best beans. Different types of equipment work best with different grinds of coffee. An espresso maker is at one end of the spectrum, and takes very finely ground coffee, like an espresso grind or a Turkish grind. Medium-fine grinds work well for drip coffee machines and pourover cones, while coarse grinds work best for French presses.
You should also consider how you'll be taking your coffee to make sure you get the best coffee experience. For instance, if you prefer to drink your coffee with milk and sugar, you may want to choose a less acidic type of bean, or a coffee that has a little stronger taste so that it won't be too diluted by the milk. Nutty coffees also tend to work well with milk. If you prefer to drink your coffee black, but not too strong, then you may want to go for a medium bodied, medium roast arabica coffee that was grown beneath 4,000 feet (1,219 m). Many coffee experts suggest tasting a little bit of any coffee before putting any milk, sugar, or flavorings in, as this can give you a better idea of the true taste of the coffee and help you decide whether any additional flavorings will mesh well.