Can the coffee be heated twice to warm it up when it is cold? Why doesn't cold coffee taste so good?

Everyone knows that brewed coffee will naturally cool down over time, but in addition, during this process, its taste will also undergo irreversible changes. For example, the original rich aroma has disappeared, the deep-roasted coffee has become less smooth, and the middle-and-lightly roasted coffee has become more sour and astringent, and may even produce a lot of bitter or mixed endings.

Why does coffee change so much from hot to cold?

The aroma, sweetness and bitterness of a freshly extracted cup of hot coffee are the most obvious. After the coffee is cooled, the sour coffee will become more "sour" and the bitter coffee will become more "bitter". Although the tonality of the taste is still the same as at high temperatures, the coffee is no longer "fragrant". There are two main reasons behind this. One is the chemical changes caused by coffee changing from heat to cold, and the other is that our senses also change as the liquid cools down.

As mentioned in a previous article in Qianjie, not only the sweet, sour, bitter and sweet taste on the taste, a large part of the flavor we taste when drinking coffee comes from its aroma. When the coffee is freshly brewed, it carries more volatile flavor substances and spreads out with the heat. This is also the best time to feel the aroma of flowers, fruits and caramel. After the coffee cools completely, a large part of the volatile flavor substances have disappeared into the air. When you smell it again, only a faint "coffee flavor" may remain.

If you look carefully, you will find that after hot coffee is left for a long time, there will be white flakes floating on the liquid surface. This is an oxidation reaction caused by direct contact between the oil and the air. Because there is no support from the oil, so the coffee does not taste so smooth. In addition, cool coffee will appear cloudy than when it is freshly brewed. This is because of the condensation of some of the substances in it after cooling down, which is why cold coffee sometimes tastes rough.

Finally, back to our senses. When the temperature of coffee is lower than our body temperature, as the coffee continues to cool, our taste buds gradually become less aware of sweetness, while at the same time, their perception of bitterness continues to increase. Therefore, for lightly roasted coffee that emphasizes fruit acid, the sourness will be particularly obvious when it cools; for deep-roasted coffee that mainly suffers from bitterness, the temperature drop will lead to a low sweetness perception, and the bitterness in the coffee will also be exposed.

After the coffee has cooled, should it be better to reheat it or add ice?

Although we know that the coffee that has been completely cooled is no longer so good, we still drink it all out of the spirit of not wasting food. At this time, some friends also choose to take some "first aid measures", such as reheating the coffee, or adding ice cubes to cool it down into a cup of iced coffee. So, will this taste good?

A comparison test was set up on Qianjie here, which was to brew two different pots of coffee, taste it while it was hot and record it, then let it cool naturally at room temperature, then take part and re-heat it to 55 - 58℃, and add some ice to cool it down to 6 - 8℃ (remove the ice cubes), and finally compare the taste differences between them again.

The coffee beans were selected from Qianjie Kafa Forest, which is a representative of medium and shallow roasting, and Qianjie Huilan, which is a representative of medium and deep roasting. Both of them were washed with water. The clean conditioning properties allow us to better feel the changes in coffee.

Kafa Forest extraction parameters are 16g coffee powder, 1:15 powder-water ratio, water temperature of 92℃, grinding degree, hand-brewed fine sugar (EK43s scale 10 grids/C40 scale 24 grids), V60 filter cup, three-stage (30g+105g+105g);

The extraction parameters of washed GlenWhelan are 16g coffee powder, 1:15 powder-to-water ratio, water temperature of 88℃, grinding degree, hand-brewed coarse sugar (EK43s scale 10.5 grids/C40 scale 26 grids), KONO filter cup, three-stage (30g+105g+105g).

Coffee status/coffee beans

Qianjie Kafa Forest

Qianjie Gelun Whelan

Just after washing (70℃)

Flowers, cherries, grapefruit, citrus, green tea, cream melon seeds

Stir-fried hazelnuts, black cocoa, slightly smoky taste, obvious sweetness

Heating back to temperature (55~58℃)

Grapefruit, green grape, sour taste, astringent citrus peel

Cocoa, nuts are sweet, almond is bitter, and the flavor is weak

Add ice to cool down (6~8℃)

Citrus, melon seeds, mostly tea-like, sour and refreshing

Dark chocolate aroma, thin taste, short finish, not bitter

By comparing the above results, it is not difficult to find that whether the cooled coffee is heated and reheated or added extra ice cubes to cool down, the flavor is difficult to reach the richness of the flavor when it was first washed out, which shows that this is an objective fact. But when you are faced with a situation where coffee is really difficult to swallow after cooling, you can actually find some "first aid measures" from it.

For lightly roasted fruit acid coffee, the most negative taste after cooling is mainly sour and astringent, so we can weaken it by adding ice to make the coffee easier to eat. The disadvantage is that the coffee will become lighter, so drink it as soon as possible;

However, for deep-roasted bitter coffee, because it contains more bitter substances, it is often more obvious after cooling. At this time, heating or adding ice can make the coffee show different effects.

When coffee is heated back to close to human body temperature, the taste buds 'sense of sweetness is "activated", which can cover up the bad bitterness and make the coffee "sweeten" again; and when we add ice cubes to room temperature coffee, the tongue will be less sensitive to bitterness, making it easier to drink coffee without burden.

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