What can the Crema of Espresso tell us about coffee basics?

During the roasting process, a large amount of carbon dioxide is produced in the coffee beans, most of which will be emitted during the cooling process, and a few will continue to be kept internally, and these gases will be released when the coffee powder is ground, so coffee must be made as soon as possible after grinding. When hot water hits coffee powder under Espresso pressure, it will emulsify the insoluble oil of coffee powder, and at the same time, it will be supersaturated and dissolved into a large amount of carbon dioxide, which is much larger than the solubility of hot water under normal pressure, which is why countless small foams appear immediately when the liquid flows out of the handle. But that doesn't fully explain Crema. It's like opening a can of Coke and seeing countless bubbles coming up, but they don't last at all, unlike Crema.

To produce stable bubbles, we need some bubbles and some compounds to wrap the bubbles, making the bubble structure stable and elastic. The process of this chemical reaction can be thought of as the role of a surfactant, which is accomplished by a substance called protein melanin. It is produced by a chemical reaction of a group of mixtures during baking. In fact, scientists do not know much about the process. Neither protein nor protein melanin is hydrophilic, so when hot water hits the coffee pressed powder, they naturally distribute on the surface of the bubbles, giving them more exposure to the air, creating countless tiny bubbles, so we have bubbles.

There are other things-fat (editor's note: the author refers to oil and fat, fat is solid, oil is liquid), the presence of oil often destroys the structure of foam (think about it, when we make a cake, we have to remove the yolk, otherwise the fat in the yolk will cause the egg whites to fail. So will the oil in the coffee cause Crema to disappear quickly in a few minutes? The answer is both right and wrong. The surfactant is dissolved in water, and due to the action of gravity, the surfactant of the bubble surface will be pulled off the surface of the foam together with the water, making the foam fragile, inelastic, and then disappear quickly. The speed at which the foam disappears is related to the rate at which the water is dragged away, but the foam on the surface of a cup of coffee lasts much longer than the foam on the surface of a cup of coffee, because the liquid is much thicker than the rapidly extracted Espreeso, which is confirmed by our taste.

Espresso made in 15 seconds usually has a whiter Crema because it is relatively light in extraction (low concentration). Coffee powder is quenched in water for a relatively short time, and the stickiness of coffee is lower than that washed out in 25 seconds. For the same reason, coffee made from a lower water temperature will be lighter because it does not have enough energy to dissolve the substance in the coffee (water with low water temperature has low solubility). This also explains why excessive quenching can cause the color to be as dark as scorched.

For a long time, there has been a theory that Robusta can produce better Crema during extraction. This is true because Robusta coffee beans contain only half the aroma components and aromatic oil content of Arabica coffee beans. This means that less oil is extracted into the coffee, thus reducing the effect of oil on foam stability, so increasing the Robusta coffee beans will reduce the overall amount of oil quenched from the coffee powder, which means that you have a higher chance of making a more stable and richer Crema.

Of course, there are a variety of uncertainties that affect Crema. In general, it is how coffee preserves the foam of carbon dioxide, how many kinds and how many oils there are in coffee, and how they are quenched into the cup.

Crema can tell us:

1. Whether the coffee is fresh.

A large number of robusta beans allow us to see a lot of bubbles, so we can't judge the freshness of coffee by watching the speed at which the bubbles disappear. Fresh coffee will have a lot of Crema during the whole brewing process, that is, when the coffee comes out, it looks like Coke. Only when the extraction is nearing the end and a large amount of water appears, will it stop, so that two very obvious stages of the process can be clearly observed. Stale coffee beans often see a thin, separate Crema, and the resulting coffee is often thin and watery, meaning less Crema and faster disappearance.

2. The degree of coffee extraction

The deeper the Crema, the more dissolved matter gets into the cup. (contains over-extracted coffee impurities)

3. The uniformity of coffee extraction.

The more stable the Crema, the better and stronger the coffee we make, and it means that there are fewer gaps in the coffee powder (channel effect) and fewer mistakes in the production process.

What Crema can't tell us:

1. Is the coffee good?

As long as enough fresh, no matter how bad beans, no matter how bad baking can produce rich Crema.

2. The oil in the coffee is properly emulsified

For a long time, many people, including I thought, Crema told us the degree to which the oil in coffee is quenched, that is, the more Crema, the more oil in coffee. But the theory tells us that the more oil there is, the less bubbles it contains. If you try making espresso with 5-6bar pressure, you will find that you can still make a lot of Crema (fresh coffee beans are easy to repeat this experiment), but the coffee tastes very insipid because of lack of oil and aroma.

It's not complicated at all!

Espresso and Crema are often complicated in coffee making, far more than needed. In the whole production process of Espresso, Crema is a very simple link. There are three main elements in Espresso, one is water, the second is oil, and the third is foam. The body of Espresso is gelatinous, and the oil in coffee is emulsified by hot water at high temperature and high pressure to form a colloid, which is extremely stable. The foam on the surface of Espresso disappears very quickly compared to the colloid. After eliminating the mysterious aura shrouded in Crema, Crema is still a great pleasure of Espresso. Its honeycomb structure stores a lot of aromatic substances, releases a large amount of fragrance when the structure disintegrates, and brings enjoyment to our vision and smell at the same time.