I welcome you to a new article where I will answer some questions I have been asked a lot: What do I do when my coffee gets cold? Can it be reheated? Is there any way to preserve it? What is the best way to keep it warm?
I think it has happened to all of us at some time when we have prepared a delicious coffee. We want to wait until the temperature drops a little bit to drink it, but for some reason that keeps us busy, when we remember our cup, the coffee has already cooled down completely, and the truth is that it is very sad to have to throw away this coffee to prepare a new one.
We need to know a few things before answering these questions, and below I will detail each one.
The coffee oxidation process
As I have already told you in other articles, coffee beans go through the oxidation process from the moment they are roasted. The more time goes by, the more these beans lose gases, such as carbon dioxide, in what we call degassing, and with the passing of weeks and months, they begin to lose aromas and develop flavors that are not very pleasant.
For this reason, it is always better to keep the coffee in beans and not ground, since otherwise, this will happen much faster. It is also important to keep it in specific containers, as I have told you in this other article on how to preserve fresh coffee for longer.
So, when we prepare a coffee, that is to say, when we add hot water to the ground beans, this oxidation takes place quickly, in a matter of hours.
For example, when we cut a fruit such as an apple, a pear, or a banana, each minute, it oxidizes and changes its color, texture, and flavor until, with time, it rots directly. As coffee is a food, something similar happens to it.
How temperature affects coffee
To begin with, coffee with different temperatures will change chemically, and we will perceive different aromas and flavors from before the extraction until the beverage cools down completely. The coffee will release volatile compounds that are the ones that contribute to the aromas and flavors that we perceive.
From the moment we begin to grind it, many of these compounds that are almost encapsulated within the beans will be released, and others will be released once they come into contact with water. Once the beverage is prepared, with the high temperatures, the coffee releases a lot of steam which enhances the perception of the aromas but can inhibit the perception of the flavors.
As the coffee lowers its temperature, we can suddenly feel other aromas. Still, it is very difficult to feel the characteristic flavors of a coffee beyond perhaps a generic roasted and bitter taste until around 122 degrees Fahrenheit.
When we reach this temperature, the aroma may not be as intense since it does not release as much steam, but the bitterness begins to diminish. The more complex flavors begin to be present, mainly the acidity. And, when it comes down a little bit more, the sweetness becomes prominent, and we can start to feel a lot of delicious flavors.
NOTE: It is worth clarifying that what I am saying only counts for high-quality coffees. Poor-quality coffee will be bitter and have unpleasant flavors from the beginning; the lower the temperature, the worse it will get.
To go from high temperatures, let’s suppose about 167 degrees Fahrenheit, after preparing it until reaching an ambient temperature, it can take approximately half an hour, depending on many things.
And as time goes by, these volatile compounds continue to be lost, and the chemical composition of the coffee changes. It is impossible to avoid the loss of these compounds; it is a reaction that begins when we put water in coffee.
Is it possible to avoid chemical changes in coffee?
What can we do? To delay this process a little, we can serve the coffee still hot and freshly prepared in a thermos, no matter which one; some are more insulating and will maintain the temperature for longer and others for less time.
For example, when I know I am going to be busy and maybe I am not going to be paying so much attention to the coffee, I leave it in one of those thermoses, and it will not cool down so fast, so I can enjoy it hotter for longer, I like it around 122 degrees Fahrenheit.
However, it is important that, if you are going to use a thermos, do not leave the coffee in there for a long time, do not leave it in there for hours because the aromas cannot evaporate, there is condensation, and the flavors of the beverage can change due to some of these chemical reactions happening in the coffee.
While you are going to drink it, I recommend doing it without the lid of the thermos or cup, if it does not have a very large hole, to feel these aromas since it greatly improves the flavor experience.
But is there any way to recover the coffee after it has cooled down? The correct answer is no due to these changes and the aromas and flavors lost as it cools.
What happens if we reheat the coffee after it has already cooled?
We have all experienced reheating coffee and ruining it to the point that it looks like another coffee. But why does this happen?
When we reheat the coffee either in a microwave, in a pot on the stove, or however we overcook it, it breaks down the mainly chlorogenic acids that are the most abundant and contribute to the bitterness in the coffee. The more we heat it, the faster all the remaining aromas and volatile compounds disappear; oxidation destroys them.
Some of the solid compounds in the coffee will dissolve again when the coffee is hot again, but many others will not, and this also causes more astringency, and we also notice that the coffee has less body.
Is it okay to heat coffee in the microwave?
After reading some articles where the microwave is used to heat coffee with some little tricks, I decided to give it a second chance hoping to find something good, and the truth is that I got a big surprise, in my article can you heat coffee in the microwave I explain it in more detail. And below, I will summarize my findings.
First, the microwave would be the most successful or the only tool to heat coffee, compared to fire, since it is undoubtedly the one that will raise the temperature as quickly as possible. And when the coffee is oxidizing, raising the temperature accentuates it, so the faster we can act, the better.
Secondly, and perhaps the most important part, is to heat the coffee simply for seconds until it reaches the temperature suitable for drinking, that is to say, about 140 degrees Fahrenheit. We do not want to exceed this temperature because we will increase the bitterness. It is also very important to place the cup well to one side of the turntable so that it will heat up as uniformly as possible.
And last but not least, it is necessary that the coffee has not spent the whole day oxidizing. We are talking about heating a coffee that has recently gone cold. In my microwave, 40 seconds was enough to bring the coffee that had cooled down to almost 122 degrees Fahrenheit.
While it was not the same cup I had tasted freshly brewed, it wasn’t bad either. It had a little more bitterness but was tasty, and I drank it all. But, taking it beyond this temperature is a disaster; it becomes unpalatable.
Once again, I have to say that I obtained a good result when heating my coffee in the microwave; with a coffee that had been prepared perhaps an hour ago, it had not oxidized, nor did the aromas and flavors disappear completely, because if that were the case, there would not be much more to do.
Perhaps you can also add some ice and drink it cold; that was always my recommendation when I had this doubt; with this solution, we are not going to feel the aromas and flavors so much because some of them have already disappeared, but we are not going to be adding other flavors such as bitterness and astringency when heating it again.
Of course, my recommendation has always been and will always be to drink the coffee as fresh as possible while it is still hot, where we will feel the best flavors. I always emphasize that it is better to prepare a smaller amount more frequently than a large batch to enjoy the coffee at its best. Besides, preparing a cup of coffee becomes a break that is a pleasure to give.