We’ve all done it: let your coffee cool on a corner of the desk or on the table, or even brew the coffee from the day before before putting it in the microwave for a few seconds. However, this banal gesture could well ruin your drink… and sometimes pose a hygiene problem, especially if it contains milk. Dietician-nutritionist Orlane Fagnoni explains why this reflex is far from ideal, and what alternatives to favor.
Uneven reheating which alters the taste
The first problem with the microwave is its lack of uniform heating.
“Microwaves tend to create very hot areas and others much colder”recalls Orlane Fagnoni. This operation is well known in food safety: this is why we recommend stirring food halfway through cooking and letting it rest.
Applied to coffee, this causes a mediocre result: you end up with a hot surface and a still lukewarm, sometimes even cold, base.
“We can then obtain a coffee that is burnt in places, with distorted flavors, and a completely bland bottom of the cup”specifies the specialist. With the added risk of burning your tongue or palate.
Lost aromas, accentuated bitterness: a reheated coffee no longer has anything of the original coffee
Coffee is one of the most aromatically complex drinks: more than 800 volatile compounds contribute to its scent and flavor. Once served, these aromas escape naturally upon contact with the air.
“Heating them in the microwave does not bring back the aromas”explains Orlane Fagnoni. “Just because your coffee is hot again doesn’t mean its aromatic qualities return.”
Worse still, areas of excessive heat generated by the device can enhance bitterness, increase acidity, and result in a flat, aggressive or unbalanced coffee. Clearly, reheated coffee is no longer really… coffee.
Latte coffee, cappuccino: a hygiene risk not to be ignored
In addition, when your drink contains milk, whether animal or vegetable, the issues are no longer just taste. But also sanitary.
“A latte or cappuccino left for more than an hour at room temperature becomes a breeding ground for microbial development”warns the nutritionist.
The rule is simple. Such coffee must never remain
- More than an hour at room temperature;
- Two hours maximum in a cool environment.
And above all, reheating in the microwave does not kill bacteria that has already developed. “Putting a latte back in the microwave that has been left out for an hour or two doesn’t make it any safer. In this case, it is better to throw it away and get another one.”
What to do instead? Recommended solutions
Fortunately, there are several alternatives that are much more respectful of taste and safety.
- Prevention: use a thermos cup. “A good insulated cup with a lid will keep your coffee hot for a long time without altering the aromas”, recommends Orlane Fagnoni. This is the simplest and most effective solution;
- Reheat gently in a saucepan. “For filter coffees: Very gentle reheating, while stirring, works very well.”. The heat is progressive, uniform, and does not attack the aromas;
- The Mug Warmer: the cup warming plate. This little accessory keeps the drink at a gentle temperature without its cup, without “cooking” the coffee. Ideal for those who drink slowly;
- If you really only have the microwave…. So use it as a last resort, and in a controlled manner:
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- Heat in short intervals of 15–20 seconds;
- Stir between each interval;
- Let stand 30 seconds to 1 minute to even out the heat. “This is the only way to limit breakage and avoid hot and cold coffee at the same time”, concludes the dietitian.
As Orlane Fagnoni summarizes: “You’re not going to get poisoned by reheated coffee, but you’re almost always going to alter its taste…and the pleasure that goes with it.”