Reheating coffee is not harmful: no evidence links warming an already brewed drink to harmful compounds. Acrylamide, the usual worry, forms while roasting the bean rather than in the cup, and reheating adds none. What does change is the taste, because heat drives off the volatile aromas and sharpens the bitterness. Reheated coffee is worse, not dangerous. Below you will find what actually happens and the best way to handle leftover coffee.
Before we talk about how to reheat coffee, let's explain some chemical processes that occur during roasting, brewing and subsequent heating. It is these that have a major influence on the taste and aroma.
The green coffee bean contains more than 800 different compounds. For simplicity's sake, let's divide them into two groups:
During roasting, thenon-volatile compounds contained in the coffee beans are broken down by heat to form other compounds that directly affect the flavour and aroma of the coffee. However, these compounds formed during roasting are very sensitive to heat and if the coffee is roasted longer, they will burn and the coffee will lose its taste and therefore its quality.
The next step in changing the chemical and therefore flavour composition is the final brewing. Hot water again extracts certain coffee compounds that are pleasing to our taste buds and olfactory cells.
However, too high a temperature will release undesirable substances (e.g. chlorogenic acids) which result in a bitter taste. Therefore, it is very important to ensure the correct water temperature in all processes.
What do the preceding lines imply? Clearly that temperature laws work during roasting, brewing and heating in the same way. In all cases, we expose the coffee beans to heat and thus repeat the whole process of releasing coffee acids, compounds and oils.
By reheating, the coffee retains its caffeine content but loses its aroma and flavour. Instead, the bitterness of the caffeic acid will stand out.
From the previous description, it is already clear that the right temperature is crucial. Therefore, always choose the lowest possible heating temperature to avoid negative chemical reactions as much as possible.
Heat the coffee evenly to a temperature of up to 60 °C. This temperature is lower than when brewing fresh. It is usually around 75 °C. This low temperature both mitigates most of the chemical changes and it has been found that most people prefer coffee at 60 °C because it gives the right taste experience.
1. On the stove
Have you brewed a cup of coffee and suddenly noticed it has gone cold? Don't despair.
This method works only for coffee that is fresh and has not been sitting on the table for several hours. If you try to reheat forgotten coffee, you probably won't enjoy it.
2. In the microwave
Of course, you can also use the microwave to heat it up. However, there are rules to follow here too:
This will reduce the likelihood of scorching, and therefore bittering. If this does happen, you can soften the bitter taste with cream or milk.
Reheating can precipitate the milk components in the coffee and the resulting effect will not be pleasing to your eye, let alone your palate.
It is also important to remember that dairy products must be kept cool to prevent the spread of unwanted microbes. Just pouring milk or cream into your coffee and leaving it on the table for a long time, out of the fridge, will not add to its quality. If you choose to heat the drink extra, it cancause digestive problems after drinking it.
Rapid heating to a very high temperature will burn the ingredients in the coffee, giving it aburnt aftertaste.
Many drip coffee machines have a feature that keeps the beverage in the potwarm for several more hours after brewing. This may seem like a useful feature at first glance, but believe me, over time it detracts from the quality of the coffee you brew. It loses the integrity of its flavour and becomes bitter.
Although the coffee grounds remain in the filter when brewing drip coffee, some finely ground particles may escape into the pot (as they do when using a French press). The particles continue to boil during the heating process and this long leaching process brings back the unwanted bitterness.
To avoid unnecessary heating of the coffee, I recommend the following:
Gently. Use low power in the microwave in 20-second bursts, or a saucepan over low heat, and stop well before boiling. Boiling drives off what aroma remains and concentrates the bitter compounds.
No. There is no evidence that reheating a brewed coffee creates harmful substances. The WHO removed coffee from its list of possible carcinogens in 2016, flagging instead the risk of any drink served above 65 °C.
The volatile aromas have already escaped and heat drives off more, while oxidised acids stay behind. The balance shifts towards bitterness, which is why the second cup never matches the first.
Around two hours for taste, barely longer in a flask. After that it is still safe but flat. With milk added, treat it like milk and finish it within two hours at room temperature.
Cold, ideally poured over ice. Leftover coffee makes a decent iced coffee, whereas reheating never brings the lost aroma back.
Mohlo by vás zajímat: Cold brew - what you (might) not have known
