What is the reason for the expansion of coffee? Does stuffy steaming not expand mean that the coffee is not fresh?

It is believed that you will see a phenomenon when you have made coffee by hand or when you have seen others make coffee, that is, when the water begins to come into contact with coffee powder, there will be bubbles coming out, and the coffee powder will swell. It is also possible that the size of the foam coming out of each brewing time, how much, the degree of expansion of coffee powder is often different.

What on earth are these bubbles?

In fact, the gas in the bubble is the carbon dioxide produced when roasting coffee beans, and the outer membrane of the bubble is formed by coffee proteins or polysaccharides (the same fraction of bubbles covered by Italian espresso). Going back to the question just now, the extent of the coffee foam is actually caused by different ways of releasing carbon dioxide.

Is it true that the more bubbles, the better the coffee beans?

Freshly baked coffee beans are rich in carbon dioxide. If they are immediately ground into powder and poured into hot water, a large number of bubbles will be produced. These bubbles stop the extraction of coffee, not that the beans are bad. So we should take a correct look at your problem, and if you make coffee at this time, it will taste lighter than usual. Then the freshly ground coffee beans are usually put for one night before use.

Is it because the coffee powder is not expanding, that is, the coffee is not fresh?

In fact, this is also a big misunderstanding, whether there are bubbles and the degree of expansion of coffee powder is related to the amount of carbon dioxide in coffee powder, of course, if it does not expand much, it will be thought to be because coffee powder is not fresh. Indeed, with the passage of time after baking, there will be less and less carbon dioxide in coffee beans. However, the reason why coffee powder does not expand easily may also be due to the addition of a deoxidizer that absorbs carbon dioxide, or the use of coffee powder with large particles and slowly pouring into hot water, as well as water temperature permitting. So we can't generalize.

Generally speaking, deep-roasted coffee is more likely to bubble.

Because in the roasting process of coffee beans, coffee beans will begin to change chemically. after the occurrence of one explosion and two explosions, the fiber gaps in coffee beans will become larger and bigger, and some of them will even break, so deep-roasted coffee is more likely to bubble when brewing. And the time of bubbling is shorter than that of shallow roasting. In series, the light-roasted coffee bean fibers touch more closely, the gap will be very small, and the contact surface with water is smaller than deep-baking, so you will see that the light-roasted coffee powder will soak slowly and last for a long time in the process of hand-brewing coffee stewing.