CO2 | The Spark Plug

April 16, 2018

Let’s get one thing out of the way right up front: crema in and of itself says little about the quality of your espresso, and is really only an indicator of the freshness of the beans and the quality of extraction. Also, certain roasts and beans are conducive to better formation of crema, but not necessarily cup flavors.

 

That said, we at Flair want to emphasize that if you are looking for more crema atop your espresso, it’s best to focus first and foremost on sourcing freshly roasted whole beans and grinding them moments before extraction with a quality burr grinder. These ‘moments’ matter as is demonstrated by the following video showing the difference between extracting 30 seconds, 30 minutes and several hours after grinding the same beans— that were home-roasted less than 48hrs prior to these pulls.

 

 

 

The crema you see in the freshly ground example is arguably too much. Yes, too much of a ‘good thing’ can be a bad thing. For this post, however, we merely want to call your attention to the fact that you will find no crema-love in pre-ground or otherwise stale beans because they have lost nearly all their stores of crema-generating CO2 gases--a byproduct of the roast. While the degassing period of whole beans takes place over several weeks, the degassing period of beans immediately after being run through a grinder accelerates to just minutes and hours. Grinding beans is a highly destructive process that liberates the CO2 stored in a multitude of pockets of the porous beans while also increasing the surface area now exposed to the environment. This speeds up the transmission of gases as well as triggering a significant loss of aromas. Within a few short days the freshly roasted coffee has already lost 30-40% of that CO2 and the remainder within a few short weeks.

 

The easiest way to conceptualize this it to think of what happens to a can of soda within minutes after you crack the top. It goes flat of course. I’m certain you’re quite familiar with how long you have to enjoy that soda before the time to pour it down the drain arrives,. You should start thinking the same way about your coffee in relative terms of freshness and crema potential. Once ground, coffee should be extracted within seconds –definitely the first 15 minutes – for best results. This is one reason why preground coffee—whether off the shelf at your local grocer or from your local coffee shop even the day before—will never yield crema, rich aroma and flavor. The other reason, though, is no coffee shop or roaster will ever be able to provide a single grind that will work optimally for the myriad of espresso machines out there. As we said at the top of the post, crema is an indicator of freshness and proper extraction, and preground coffee fails to deliver on both fronts.

 

In future posts we’ll discuss the merits of resting your beans for at least a few days prior to extraction, how more lever pressure than the recommended 30-40 pounds does not in fact improve espresso quality, and many other topics to help you up your espresso game.

 

In the meantime, if you'd like to go down the rabbit hole a littler further, the following article will more than satisfy your curiosity and need for hard data:

Time-Resolved Gravimetric Method To Assess Degassing of Roasted Coffee

 

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