Why does the hand coffee turn sour when it gets cold? The solution to the fact that coffee becomes unpalatable after cooling.

A friend asked in front of the street, "Why is it that the Yega I just washed is so sour and sweet that it is so comfortable that it becomes as sour as lemon after it is cooled?"

This is a very good question, especially when we make shallow roasted coffee, the freshly brewed coffee is rich in aroma, the sweetness of the fruit is obvious, and after cooling, it becomes very sour. I believe many friends have encountered this phenomenon, but they can't understand why it happens. Qianjie would like to take this opportunity to share this knowledge. First of all, light roasted coffee will feel sour when it is cooled, which is a normal phenomenon. There are two angles causing this phenomenon, the first is the perspective of people's senses, and the second is the angle of the change of coffee itself. Our senses also have different degrees of perception of the five flavors at different temperatures. In coffee, the closer we are to the room temperature, the more obvious our perception of bitterness is; for sweetness, it is the highest when it is close to human temperature; for sour taste, our perception does not change significantly with the temperature.

In a cup of shallow roasted coffee, the bitter substance itself is relatively few, and there will not be much taste change. And the largest number of acids themselves we do not perceive as the temperature changes. The main reason is that when the coffee gets cold, our perception of sweetness is not as obvious as when it is hot, so when the sweetness weakens, the sour taste is naturally obvious.

Then there is the change of coffee over time. We can taste the flavor of coffee, a large part of it comes from the aroma of coffee, when the coffee is still hot, emit more aroma, such as we smell peach, strawberry jam, honey in the aroma of coffee, naturally, coffee also adds sweetness. The temperature dropped, the aroma of the coffee is not so obvious, and naturally can not feel those "sweet" taste. Generally speaking, when coffee cools down, its acidity is more obvious than that of hot, and its flavor is not as rich as that of hot. In the case of Yejia Xuefei coffee, when it is hot, you can clearly feel citrus, flower, honey and green tea. After cooling, there is only pure citric acid and green tea rhyme.

Some friends like to taste the high, medium and low temperature of coffee, and think that a good cup of coffee should have a good performance in high, medium and low temperatures. Qianjie agrees with this view very much, but it should be restricted in terms of time. For example, if the time for a cup of coffee to be brewed to room temperature is about 40 minutes, then we should set the tasting time to 40 minutes. As for the coffee after 40 minutes, the temperature has been maintained at room temperature, 2 hours later to taste, it can not represent the low-temperature flavor performance. Because in such a long time, coffee may appear oil oxidation (surface oil caking), condensation (coffee liquid turbidity) phenomenon, there will be bitter, astringent, fuel consumption taste.

Another exception is that hot drinking does not have any negative flavor, and as the temperature drops, the bitter taste becomes more and more obvious. This is because as the temperature drops, the taste of tannin is released, resulting in a bitter taste. This may be caused by brewing, when making coffee, it will inevitably dissolve the tannins of coffee, just a matter of how much. The problem is that tannic acid is dissolved more, but it does not drink it when it is hot (high temperature is not sensitive to bitterness), and when the temperature comes down, the bitterness is easily perceived.