Crema in espresso is often seen as an indicator of a “good” espresso but what forms this crema? Crema is the result of the reaction of water hitting freshly ground coffee at an instant. The crema that forms at the top of the espresso is created by CO2 gas that is released from the coffee during extraction.
It is known that this CO2 reaction adds bitterness to the cup. If that’s the case, then would the espresso taste better if there was less crema? Our question: if we pre-ground the coffee it and give it some time to de-gas (get rid of some CO2 in the coffee) before pulling the shot, what will happen to the taste of the espresso?
Our Experiment:
We pulled 2 espressos – one using pre-ground coffee, and another using freshly ground coffee. One would think the espresso that was freshly roasted would taste better, because aesthetically, it does look better due to its thick and foamy crema; however, the result is quite the opposite. The freshly ground coffee tastes good, but the acidity is much sharper and the medicinal bitterness is much higher. The pre-ground coffee however, had a much softer acidity, higher sweetness, and noticeably lower bitterness. The overall balance was much better as well.
This makes sense when you compare this process to pourover coffee. Pourover coffee needs time to de-gas (“bloom”) after the first pour for around 30 seconds. The purpose of this step is to release some of the trapped CO2 gas that disrupts the extraction process. In the same way, if we pre-ground our coffee for espresso, we are essentially accelerating the “bloom” phase of the coffee to create a much sweeter and flavourful cup. Although it may produce less of that foamy crema that you’re used to at the top of the espresso, the tradeoff is you get a much tastier cup of coffee.
The Technical Stuff:
We measured Total Dissolved Solids (TDS) of both espressos, and it showed that the pre-ground coffee had a lower TDS than the freshly ground one. TDS indicates how strong the coffee is, hence the definition - total amount of coffee solids dissolved in the final output of beverage, and it is directly related to bitterness in coffee. If this is the case, then the lower TDS explains why the pre-ground espresso was much sweeter and less bitter then the freshly ground coffee.
Going Forward:
These findings are the reason why we pre-ground our espresso in the café and keep them in small individual, air-tight jars. If you ask me, the noticeable increase in sweetness and reduction of bitterness and acidity is well worth the prepping time and effort.
