Espresso is nothing more than an emulsion (a liquid composite made up from stratified oils), and to make one shot of espresso, it requires 50 coffee beans.
But, like almost everything in coffee, there’s a lot more science than first meets the eye, and espresso is about as scientific as a black hole.
In this blog post, we’ll reveal all we know about espresso crema, and why it’s extremely important when it comes to pouring the perfect shot.
What is espresso crema?
Espresso crema is the tan-coloured foam that sits on top of the liquid in an espresso. It’s a sure sign that you’ve pulled a good shot of espresso, and that your flavour profile will be well balanced.
What crema does, then, is give a cup of espresso a fuller and more rounded flavour, and a longer aftertaste than, say, a cup of drip.
Emulsification and crema: what’s the science?
As we’ve explained, espresso is a liquid emulsion, and when water runs through a coffee puck, it extracts the essential minerals and ‘unloads’ them into the cup. Everything from fats, sugars, natural oils, compounds like melanoidin, and caffeine are extracted and form the makeup of the espresso.
Often, in fresh coffee, these minerals and oils exist in abundance and help form a layer of crema on an espresso. It’s why espresso crema is a sure-fire sign of a good, healthy coffee extraction.
Carbon dioxide and crema: what’s the science?
There are many factors at play when it comes to espresso crema. For the best crema (and arguably for the best espresso), the biggest consideration is how fresh your coffee beans are.
Freshly roasted coffee releases carbon dioxide into the atmosphere. It’s why coffee bags inflate on the supermarket shelf, and why they have a vent to ensure they don’t burst. It’s also why, when coffee is fresh, it has a stronger, more potent smell to it. In short, oxygen is yet to consume and kill the coffee bean. And, like us humans, it’s most alive when it’s giving off more carbon dioxide.
When coffee is ground for espresso, then, the release of carbon dioxide continues, and when an espresso shot is finally poured, micro-bubbles begin to form on the surface of the espresso crema as carbon dioxide tries to escape the cup. The trapped gas in the crema is trapped flavours, and it’s these that first hit the tongue. It’s also why a good coffee crema can sometimes hold the weight of a spoonful of sugar.
Why is espresso crema important?
Espresso crema is extremely important when gauging the extraction of your coffee. Although variables like bean freshness, grind size and the type of beans will affect the density of a crema, espresso crema will trap and retain essential flavours and minerals that make the perfect cup of espresso. Without it, we’d experience a significantly different flavour profile, which would likely consist of thin, light and dull flavours.
However, a thick crema doesn’t always mean a balanced flavour profile. If you under or over-extract your shot, for example, you may still have a thick crema. It’s this crema that traps and enhances sour or bitter flavours, rather than the balanced and sweet flavours.
Our advice, then, is obvious: Taste test your espressos. Sure, crema can help you gauge a balanced shot, but don’t take that factor at face value. After all, you’d never judge a book by its cover… would you?