Coffee is often hotter than the air temperature because it has been recently prepared with hot water or hot coffee, allowing it to retain this heat for longer.
Coffee is usually prepared by passing almost boiling water (around 90 to 95°C) through ground coffee. With such a starting temperature, it makes sense that the coffee is initially much hotter than the ambient air (20 to 25°C generally). Hot water facilitates the extraction of flavors and caffeine present in the ground coffee. As a result, most brewing methods require a very high temperature from the start, which is why there’s that "boiling" coffee sensation when we are handed a freshly prepared cup.
The water in your coffee has a high thermal capacity. This means it accumulates a lot of heat without changing temperature much. In comparison, materials like metal heat up quickly but also cool down just as fast. Water, on the other hand, takes time to heat up but retains that heat for a longer period. This phenomenon makes your coffee scalding hot when served and explains why it stays warm in your cup for so long.
The heat of the coffee is partially trapped because the cup acts as a thermal insulator. Especially if the cup is made of ceramic or porcelain, materials known for retaining heat rather well (much better than a metal cup, for example). Around the cup, the air also serves as a natural insulator: it is a rather poor thermal conductor, which slows down the dissipation of heat to the immediate environment. So your drink stays warmer for longer.
Hot coffee loses some of its heat through evaporation, with water vapor escaping above the liquid. However, unlike other highly volatile liquids like alcohol, water evaporates relatively slowly at room temperature. As a result, the heat lost through evaporation remains limited: the drop in temperature caused by this phenomenon is often quite subtle. This explains why your cup of coffee stays hot for a relatively long time without cooling down quickly just from evaporation, unlike, for example, a cotton pad soaked in alcohol on the skin, which cools down very quickly as it evaporates.
Adding milk or cream to your hot coffee can slightly speed up its cooling by increasing its surface area in contact with the air due to the change in viscosity.
A coffee served in a preheated cup can retain its heat much longer. Baristas often use this trick to enhance their customers' tasting experience.
Some studies show that the perception of heat of coffee can vary depending on the type of cup used. For example, ceramic cups seem to keep coffee hot longer than those made of glass or metal.
Drinking extremely hot coffee (>65°C) regularly could cause damage to the esophagus according to some research. The World Health Organization recommends letting coffee cool slightly before consumption.
Thick ceramic mugs retain heat better than thin glass mugs due to their insulating properties. However, a glass mug allows for faster cooling to room temperature because of its heat permeability.
Yes, adding cold milk or cream immediately reduces the temperature of the coffee, as it mixes liquids of different temperatures. This method is effective for quickly cooling your drink to a pleasant drinking temperature.
Coffee and tea served at the same temperature theoretically have the same heat from the start. However, certain factors such as the type of cup used, the amount of steam produced, and your personal feelings can influence the perception of warmth. The strong and bold flavor of coffee can also enhance this impression.
The generally recommended temperature for comfortably drinking a hot coffee is between 55°C and 70°C. Above 70°C, the risk of burns increases significantly.
Generally, a cup of hot coffee takes about 20 to 30 minutes to reach a temperature close to that of the surrounding air. However, this time can vary depending on the initial temperature of the coffee, the room temperature, the material and shape of the cup, as well as air movement.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
