What is the reason why coffee powder starts to bubble and expand when poured into water? Is it because the coffee is not good or fresh?

I believe that if you have brewed coffee yourself or seen others brew coffee, you will have seen a phenomenon, that is, when water starts to contact coffee powder, bubbles will appear, and the coffee powder will expand. Another situation that may happen is that the size and amount of foam that comes out and the degree of expansion of the coffee powder are often different each time you brew.

What are these bubbles?

In fact, the gas in the bubbles is carbon dioxide produced when roasting coffee beans, and the outer membrane of the bubbles is formed by coffee proteins or polysaccharides (the same as the bubbles covering the surface of Italian espresso). Back to the question just now, the degree of coffee foam is actually caused by the different ways of releasing carbon dioxide.

Does the more bubbles there are, the better the coffee beans are?

Freshly roasted coffee beans contain a lot of carbon dioxide. If you grind them into powder immediately and pour hot water into them, a lot of bubbles will be produced. These bubbles will hinder the extraction of coffee, but it does not mean that the coffee beans are bad. So we have to look at your problem correctly, and if you brew coffee at this time, the taste will be lighter than usual. So usually the newly ground coffee beans are left overnight before use.

If the coffee powder does not expand, does it mean that the coffee is not fresh?

In fact, this is also a big misunderstanding. Whether there are bubbles and the expansion degree of coffee powder are related to the amount of carbon dioxide in the coffee powder. Of course, if it does not expand much, people will think that it is because the coffee powder is not fresh. Indeed, as time passes after roasting, the carbon dioxide content in coffee beans will become less and less. However, the reason why coffee powder is not easy to expand may also be because deoxidizers that absorb carbon dioxide are added during packaging, or because of the use of large-grained coffee powder and slow pouring of hot water, and the low water temperature. So it cannot be generalized.

Generally speaking, darker roasted coffee is more likely to bubble

Because during the roasting process, coffee beans will undergo chemical changes. With the occurrence of the first and second cracks, the gaps between the coffee beans' fibers will become larger and larger, and some will even break. Therefore, dark roasted coffee is more likely to bubble when brewed, and the bubbling time will be shorter than that of light roasted coffee. On the other hand, the fibers of light roasted coffee beans are more closely connected, the gaps will be smaller, and the contact surface with water is also smaller than that of dark roasted coffee beans. Therefore, you will see that during the steaming process of hand-brewed coffee, the light roasted coffee powder will bubble slowly and for a longer time.

Now everyone knows the principle behind this, let’s travel with Xiaolu in the world of coffee knowledge and make more and more progress on the road of coffee.

Part of the article is from the Internet