An integral part of the espresso process is the coffee beans being used. Coffee beans impact the flavor, aroma, consistency, and acidity of shots. However, the effect of the beans does not stop at the type of bean or region of growth. Espresso beans are greatly impacted in their taste, and consequently the taste of the espresso, by the grinding process.
Most gourmet espresso machines call for only whole bean espresso. Some best espresso machine with pods of pre ground coffee. Most places that sell whole bean coffee will usually sell pre ground coffee too. This can all be confusing for the beginning barista, so here is a quick overview of the differences.
Pre ground pods of coffee have already been ground and compressed to make them faster and easier to use. But because they have been ground days, weeks, or sometimes months in advance, there is a higher chance that the coffee will have an impaired taste. Some baristas have complained that pre ground pods tend to taste much more bitter because the pressurization process traps all the bitter tannins of the coffee beans in the pods.
Pre ground espresso grounds that have not been pressure shaped are also used by some baristas. While these grounds usually do not have the bitterness associated with pods, they also tend to unreliable flavor, as many baristas have found. The reason for this is that even though pre ground grounds come in airtight packages, the oils of the beans that have been released by the grinding process seep down to the bottom. This makes the top grounds taste flavorless and old, and the bottom grounds taste bitter and burnt. Even when mixing the bottom with the top, the taste is nowhere near that of fresh ground beans in regards to quality, consistency of the crema, and smoothness of acidity. The only thing in favor of pre ground grounds is that they do cut out part of the time it takes to pull a shot.
Whole bean espresso beans is what most major espresso franchises and gourmet cafés use. The reasons for this is that even though it takes longer to freshly grind beans, beans that have been freshly ground tend to have smoother, richer, and more pronounced flavor, without the added bitterness that comes from using pods. A well trained and experienced barista using a good quality grinder can also easily match the speed of a barista using pods or pre ground. In the end, the benefits of whole bean out weight the time costs.
When grinding whole bean espresso beans, the setting size of the grinder depends entirely on which make and model of grinder you use, as well as which make and model of espresso machine you have. Playing with the grind size till you find the perfect size for your espresso machine is part of the fun of being a barista. And once you find the perfect size, you can then easily make amazing coffee over and over again, with little adaption.
A few final comments: never grind more beans than a single shot will take. Otherwise, the same oil seeping principle that occurs in pre ground bags starts to happen. Grinders should also be cleaned frequently as they accumulate espresso bean oil on them, which goes rancid with age and will affect your shots. Finally, remember that even though there is a lot of detail, never forget to have fun and enjoy what you are doing. Espresso is, after all, very fun!