Even though coffee has been drunk for centuries, espresso only came about at the beginning of the twentieth century, after numerous Italian inventors took on a quest to make stronger and purer coffee. The experimental methods varied but they all worked around brewing the beans under high pressure for a short amount of time instead of the typical steeping and pouring. All the testing and trying resulted in the densest coffee ever made, and as a consequence of the pressure used in this process for the first time, coffee goes through a carbonation process. 


If you’ve ever had a good espresso, you’ve noticed the thick layer seating on top of the dark liquid. That’s crema, and while the word translates to cream, crema is actually a foam. Back in the 50s, when espresso machines hit the market, that foam was simply a side effect from the pressure in the machine. Basically, the coffee is carbonated the same way soda is carbonated and the foam on top of the espresso is not much different than the foam on top of a soda or a beer. When coffee beans are first roasted, carbon dioxide is locked inside and later released under the pressure of the espresso machine. 


Espresso is the only way you can enjoy a “coffee foam” as it cannot be achieved through any other coffee brewing method. All other methods allow oxygen to escape and therefore do not produce the foam or as we call it, crema. This also means that crema is made up of components of coffee that cannot be sensed and enjoyed otherwise. 


Timing is crucial for this. Once you let the coffee sit for long, the crema will slowly disappear and the taste of the espresso will change. If a barista ever dares to offer you an espresso without crema, there is a good chance that espresso sat there before you walked into the shop. Crema can tell us even more about the freshness of coffee. If the coffee beans have been sitting around for long after the roasting process, the less crema you’ll see in your espresso as carbon dioxide slowly dissipates after roasting. In short, an espresso with a thick and dense foam on top is a good quality espresso, as the foam indicates that a fresh bean has been properly extracted.


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