Crema ---- grease layer.
Almost many people are interested in the golden color of Espresso's golden top layer for coffee grease?
Although it does look very greasy,
But take a closer look,
You'll notice a lot of dense, thick little bubbles inside.
Crema is made up of these small bubbles:
Espresso is also due to the smooth taste of the drink
It is also because of this layer of bubbles!
So how did crema come about?
We know that Espresso is made up of Italian machines
The substances contained in the coffee are extracted at high pressure and high temperature.
So the same goes:
Since fresh coffee beans contain more nitrogen dioxide,
Italian machine through pressure extraction,
The nitrogen dioxide in the coffee is flowed out with the coffee liquid through pressure, forming a large number of small bubbles.
Due to the light density of the bubbles, they can float on the top of the liquid level,
So this layer of crema contains nitrogen dioxide substances.
⚠️ If the coffee beans are not fresh due to oxidation, (nitrogen dioxide volatilizes out)
Then there is no grease layer at the time of extraction, and the taste is affected by the lack of freshness.
But different extraction methods
Not all coffees are rich in grease:
For example, mocha pot extraction - the coffee is extracted by steam pressure, and the taste is rich, with a small layer of grease.
But the steam pressure of the mocha pot is much smaller than that of the Italian machine,
So the grease layer is not as rich as Espresso.
For example, hand-brewed coffee - the process of simmering when brewing: the process of discharging coffee powder will have a small drum bag, small bubble reaction.
This process is to fully expel the nitrogen dioxide substance in the coffee, so the hand brew coffee does not have a grease layer.
So different extraction methods can make coffee show different textures,
None of this affects the production of flavor substances in coffee.
So the grease layer is not the standard for measuring coffee.
It's just nitrogen dioxide wrapped in coffee.