What is the use of the vent holes on the coffee bean bag? What is a one-way exhaust valve? What is the difference in the material of coffee bean bags?

Most of the coffee beans on the market are packed in bags, and we can often see several holes similar to those punctured with needles. Just behind these holes, there is actually a simple exhaust device.

"one-way exhaust valve" is the name of this device, as its function is, gas can only be discharged from one direction, but not from the other direction. Qianjie often uses a metaphor to describe it, that is, "one-way street of cars" ~ then why do coffee bean bags need such a device?

Why use an one-way exhaust valve? At this time, there are witty friends to speak: in order to smell the fragrance!

Although! Of course! It is true that this stomata can play such a role, but this is not its main function, nor is it the purpose of people to develop it. Its real function, its real purpose is only one, that is-to prevent coffee bags from exploding!

It is well known that coffee beans accumulate a lot of carbon dioxide as a result of chemical reactions during baking, which are trapped inside coffee beans at first because of pressure. But as the roasting is complete, the carbon dioxide starts to be emitted after the coffee beans come out of the oven. But because the aroma substances in coffee beans are volatile, they will also continue to volatilize, especially after exposure to oxygen, the emission rate will be greatly accelerated. Therefore, we need to immediately after the coffee beans are roasted, put them in a sealed container to reduce the oxidation caused by oxygen invasion to the coffee beans and retain the flavor for a longer time.

However, here comes the problem. In the coming week after roasting, nearly 70% of the carbon dioxide in the coffee bean will be discharged, which is a huge amount of gas. In particular, the more coffee beans are roasted, the more carbon dioxide they contain and the more they emit, as shown in the following figure. (deep baked beans on the left and shallow baked beans on the right)

Coffee beans burst during roasting because they cannot hold up the accumulated steam in the body, as do sealed bags of coffee beans. Although most of the sealed bags can bear the continuous filling of carbon dioxide, they only need a little external pressure, or Boomboat when opening the bag! Carbon dioxide will burst out in one breath, directly leading to the explosion of the bag. Because deep roasting was the mainstream roasting degree of coffee in the last century, roasters at that time were greatly troubled by it. So they tried every means to deal with the large amount of carbon dioxide released in a short period of time. For example: replace the sealing bag with a harder bag or a sealed can; let the coffee beans exhaust in advance and then bag and seal, and so on.

But without exception, these methods are not widely used because of some defects. For example, it takes too much time to exhaust in advance, and it is difficult to measure, which will accelerate the oxidation of coffee beans, resulting in a more severe loss of flavor substances, which has a completely negative effect; and if the sealed bag is replaced with a harder bag or sealed jar, the cost will be too high, basically 3 to 4 times the original cost. So I walked around and finally got back to the bag. It was not until 1960 that an Italian Packer introduced an one-way exhaust valve and patented it, which broke such an embarrassing situation.

The composition of the one-way exhaust valve is very simple, a plastic shell with holes for exhaust, and a plastic diaphragm, as simple as that. The principle of one-way exhaust is also simple and easy to understand: the exhaust valve will be closed at first because the rubber valve piece blocks the hole, and under the same pressure inside and outside, the air inside can not get out and the air outside can not get in. As the coffee beans in the bag continue to exhaust, the bag will gradually be filled with gas, and the pressure will continue to increase. Until the gas is discharged to the internal pressure higher than the external pressure, the rubber valve piece will be pushed away, thus the gas can be discharged outward. When the excess gas is discharged and the internal pressure tends to be normal, the rubber valve will return to its original state and the exhaust valve will return to the closed state.

To sum up, we can know that the purpose of the one-way exhaust valve is indeed only one: "to prevent the gas from exploding the bag." The reason why we can smell the fragrance from the exhaust valve by squeezing the beanbag is that in addition to carbon dioxide, the aromatic substances are also volatilizing. So in addition to carbon dioxide, the extruded gas is also the aroma substance of coffee volatilization. Although it is claimed that it can be sealed, if you buy too many coffee beans and cannot finish them in a short time, Qianjie suggests using stickers to seal these holes so as not to cause deflation, ha ~ and the one who is squeezing and smelling incense, don't squeeze!

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