Why Your Coffee Tastes Different in Winter

If your coffee has seemed duller since the cold set in, you are not imagining it, and the beans are probably not the culprit. The most likely variable is the thing you have never thought about: the water coming out of your tap.

Coffee is somewhere around 98 percent water by weight. Whatever is in the water is in the cup, and whatever is not in the water is not extracting properly. So when the water changes, the coffee changes, and municipal water changes with the seasons.

What Winter Does to the Water

Two things, and they pull in opposite directions.

First, source water gets colder. Cold water from a deep well or a long main line sits closer to ground temperature, and it takes more energy and more contact time to bring it up to brewing temperature. If your kettle is working harder and your brew is running fast, you can end up under-extracting, which reads as sour or thin.

Second, and this is the bigger one, water chemistry shifts. When surface water sources freeze over, utilities often switch to different sources or different treatment blends. The mineral content changes. Hardness changes. The ratio of the minerals that help extraction to the ones that mute it changes with it.

You cannot taste that shift in a glass of water. You can absolutely taste it in a cup of coffee, because coffee extraction is a chemistry problem and you just changed the reagent.

The Mineral Part, Briefly

Two minerals matter most for extraction, and they are not the same as the ones that matter for taste.

Magnesium and calcium are the ones that bind to the flavour compounds in coffee and pull them into the water. More of them means more extraction. That is why very soft water, like distilled or heavily filtered, makes flat coffee: there is nothing in the water to do the pulling.

Bicarbonate is the other one. It buffers acidity. A little is good. A lot flattens the cup and mutes brightness, which is exactly what a lot of people describe as winter coffee tasting dull.

So the two failure modes are opposite. Too soft and you get no extraction. Too hard and buffered and you get extraction with the life squeezed out of it. Most winter complaints land in the second bucket.

What To Do About It

The cheap fix is to change one variable at a time and taste. The effective fix is usually one of these.

Grind a notch finer and check the brew time. If winter water is running cold and fast, a slightly finer grind restores contact time and gets you back to the extraction you had in autumn.

Brew a touch hotter. If you were at 195 degrees, try 200. Cold-weather water loses more heat on the way in, and a couple of degrees is often the whole difference.

If it still tastes flat and you suspect the water, try brewing one cup with bottled spring water as a test. Not distilled, which will taste worse. Spring water has minerals. If the spring water cup is dramatically better, the problem is your tap and not your beans, and it is worth looking at a simple carbon filter or a mineral adjustment.

The Point

Coffee is a seasonal product for a reason people usually attribute entirely to the beans. The beans matter. So does everything they are brewed with, and water is the largest ingredient in the cup by a wide margin.

So if February coffee tastes flatter than September coffee, do not replace the beans first. Change the water or the temperature or the grind, one at a time, and see which one moves it. It is almost always one of the three, and it is almost never the thing you assumed.

Stay curious. Stay crunchy. Stay cosmic.

— Sara Jane Shelvock, CEO, Torus Coffee Company LLC