Can coffee be reheated after cooling? Why does cold coffee taste less aromatic?

Everyone knows that freshly brewed coffee naturally cools over time, but beyond this, its flavor undergoes irreversible changes during the process. For instance, the once rich and aromatic fragrance has dissipated, dark roasted coffee becomes less smooth, medium-light roasted coffee emphasizes acidity and astringency, and may even generate bitter or mixed aftertastes.

Why Does Coffee Change So Much from Hot to Cold?

A freshly extracted hot coffee possesses the most prominent aroma, sweetness, and bitterness. Once the coffee cools down, acidic coffees become more "sour," and bitter coffees also become more "bitter." Although the flavor profile remains the same as at high temperatures, the coffee is no longer "aromatic." This is mainly due to two reasons: first, the chemical changes that occur as coffee transitions from hot to cold, and second, our senses also change as the liquid cools.

As FrontStreet Coffee mentioned in past articles, the flavors we taste when drinking coffee include not only the sweet, sour, and bitter sensations on the palate but also a large part from its aroma. When coffee is freshly brewed, it contains more volatile flavor compounds that disperse with the hot steam, making it the best moment to experience floral, fruity, and caramel aromas. Once the coffee has completely cooled, most of these volatile flavor compounds have disappeared into the air, leaving only a faint "coffee smell" when you smell it again.

If you observe carefully, you'll notice that after hot coffee sits for a long time, white flakes float on the surface. This is the result of oils oxidizing when directly exposed to air. Without the support of these oils, the coffee tastes less smooth. Additionally, cooled coffee appears more turbid than when freshly brewed because some substances undergo condensation as the temperature drops. This explains why cold coffee sometimes has a rough texture.

Finally, let's return to our senses. When coffee temperature drops below our body temperature, as the coffee continues to cool, our taste buds' perception of sweetness gradually decreases, while the perception of bitterness continuously increases. Therefore, for light-roasted coffees that emphasize fruity acidity, the sourness becomes particularly noticeable when cooled;而对于主打苦味的深烘咖啡而言，温度下降导致甜味感知低，那么咖啡中的苦味也就暴露出来了。

Is It Better to Reheat or Add Ice to Cooled Coffee?

Although we know that completely cooled coffee doesn't taste as good, we still finish it all to avoid wasting food. At this point, some people might choose to take "emergency measures," such as reheating the coffee to warm it up again or adding ice cubes to cool it down into an iced coffee. So, will these methods make it taste better?

Here FrontStreet Coffee set up a comparative experiment: brewing two different coffees, tasting them while hot and recording the observations, then letting them cool naturally at room temperature. Then, taking portions to reheat to 55-58°C and other portions to cool with ice to 6-8°C (removing the ice cubes), and finally comparing the flavor differences between these conditions.

The coffee beans selected were FrontStreet Coffee's Kaffa Forest as a medium-light roast representative and FrontStreet Coffee's Huilan as a medium-dark roast representative. Both were washed processed, with clean flavor profiles that allow us to better perceive the changes in coffee.

Kaffa Forest extraction parameters: 16g coffee grounds, 1:15 coffee-to-water ratio, water temperature 92°C, grind size: fine granulated sugar for pour-over (EK43s setting 10/C40 setting 24), V60 dripper, three-stage pouring (30g+105g+105g).

Washed Colombian Huilan extraction parameters: 16g coffee grounds, 1:15 coffee-to-water ratio, water temperature 88°C, grind size: coarse granulated sugar for pour-over (EK43s setting 10.5/C40 setting 26), KONO dripper, three-stage pouring (30g+105g+105g).

By comparing the above results, it's not difficult to find that cooled coffee, whether reheated or cooled with additional ice, cannot match the richness of freshly brewed coffee in terms of flavor, indicating this is an objective fact. However, when you face a situation where cooled coffee is truly difficult to swallow, you can actually find some "emergency measures" from it.

For light-roasted fruity acidic coffees, the most common negative flavors when cooled are sharp acidity and astringency. We can mitigate this by adding ice to make the coffee more palatable, but the drawback is that the coffee becomes diluted, so it should be consumed quickly.

However, for dark-roasted bitter coffees, which naturally contain more bitter compounds, these become more noticeable when cooled. At this point, reheating or adding ice can present different effects.

When coffee is reheated to near body temperature, the taste buds' perception of sweetness is "activated," which can mask unpleasant bitterness and make the coffee "sweet" again. When we add ice to warm coffee, the tongue's sensitivity to bitterness decreases, making the coffee easier to drink.

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