Coffee That's Been Up Too Late

The coffee brewer is designed to be simple. It gets water hot enough and sends it at just the right temperature through your grounds for exactly the right time. The extracted brew ends up in a container. In a perfect world, you instantly pour this liquid into your cup and drink a heavenly drink. As you slowly sip it, it changes in flavor as it cools.

Somewhere along the line, it occurred to someone that it might help to keep the remaining beverage warm, either so you might enjoy a second cup or on the chance that others might join you in a few minutes.

So, the thought of adding a hot plate underneath the brewer’s carafe seemed like a good idea. And, for a few minutes, it is a good idea. For up to about thirty minutes, the coffee kept hot in the carafe is virtually identical in flavor to the original brew. Somewhere after thirty minutes, the effect of heating the coffee begins to add a bitter note the the beverage. After a while, it even affects the aroma. Few of us fail to note this aroma, commonly present at places that offer complimentary coffee such as oil change services.

A few years back, the folks who made thermoses began marketing their products as superior to warming plates in order to preserve your coffee at just-brewed temperatures. Their claim was, and is, that coffee tastes and smells better for longer using their product. The claims vary, but I’ve read optimistic projections of hours and even conservative ones of more than an hour, with virtually no taste or aroma degradation.

Is it true?

I think the thermos offers a couple of genuine advantages. The evaporation that takes place on a warming plate is lessened in a thermos, where the steam rises and falls back into the brew. The direct heat of a hot plate, probably concentrates the heat too much on the coffee nearest it and so might be expected to accelerate any negative effects, whereas it might be effectively argued that there is inherently less of this effect using a thermos.

However, when all is said and done, my unscientific use of both over several years shows very little difference. Meanwhile, the thermos has the unfortunate and, in my opinion, far greater negative trait of offering false security. The worst of the thermos marketers presents the thermos as a virtual storage locker of coffee flavors and aromas.

Where are hot plated coffee carafe holds coffee well for up a half-hour, I find the thermos matches its flavor for maybe forty minutes. To me, that’s hardly worth the gain. Meanwhile, thermal carafes are more likely to be hard to clean with narrower necks. That would be a bigger taste threat to me.

My preference is still the hot plate and a good glass carafe. If the model offers the option, I like the hot plate to automatically shut off after a half hour.
If you must have a thermal carafe, make sure it offers a wide enough neck to place your hand and a sponge down into it. Use a small amount of fragrance-free detergent to keep it clean, or a glass carafe for that matter.

Thermos gaskets pick up odors that are hard to remove more than the plastic lids on carafes. This might be a minor point, but I think it’s valid.

Don’t buy anyone’s claims that coffee can be kept warm for an hour or more, regardless of the method. It just ain’t so. Coffee in a sealed thermos heats itself into bitterness.

I’ve yet to see any scientific research done that proves otherwise.