Seven mistakes that ruin a lot of people’s coffee every morning, ranked by how much damage they actually do. The first one wins by a mile, and it is not the one usually blamed.
1 · Old coffee
The mistake that ruins the most coffee by a distance, and the one least suspected, because the bag is perfectly sealed and doesn't smell off.
Whole bean coffee is good between 3 and 21 days after roasting. Ground, the window drops to around 5-7 days from opening. Past that it doesn't go bad: it goes flat, with a cardboard edge, and no technique recovers it.
Fix: buy by roast date, not best-before, and in quantities you'll finish within a month. If the pack has no roast date, that's your answer.
2 · A blade grinder
The second bottleneck, and another one people don't connect to flavour.
A blade grinder smashes the bean and produces dust and large chunks at the same time. The dust over-extracts and turns bitter; the chunks under-extract and add sourness and a watery taste. Both faults arrive in the same cup, which is why the coffee comes out simultaneously bitter and weak.
Fix: a burr grinder, even a basic hand one. It's the purchase that improves coffee most per euro spent — covered in the grinder guide.
3 · Guessing the ratio
The amount of coffee is the easiest variable to control and the one most people leave to the luck of the scoop.
- Filter: 1:16 — 60 g of coffee per litre of water. For a 300 ml cup, around 18 g.
- Espresso: 1:2 — 18 g in, 36 g of liquid coffee out.
- French press: 1:15 or 1:16.
Fix: a €15 kitchen scale. It sounds excessive until you try it; after that there's no going back.
4 · Boiling water
Pouring the moment the kettle boils over-extracts the coffee and pulls out bitter compounds that at the right temperature stay put.
The good range is 90-96 °C, and it's worth tuning to the roast: dark roasts want cooler water, around 88-91 °C, because they're far more soluble.
Fix: boil and wait 30 to 60 seconds with the lid off. No thermometer required.
5 · Grind that doesn't match the method
Each method needs a different particle size because the contact time differs: the faster the water passes, the finer the coffee has to be.
- Espresso — very fine, like slightly gritty talc.
- Moka pot — fine, but a touch coarser than espresso.
- Filter and V60 — medium, like table salt.
- French press and cold brew — coarse, like sea salt.
Fix: if you buy ground, always say which coffee maker it's for. A generic grind suits none of them.
6 · A dirty machine
Coffee oils build up and turn rancid. That rancid flavour transfers to every cup, and because it appears so gradually almost nobody notices: you get used to it without registering that your coffee got worse months ago.
Fix: rinse the portafilter and basket after every use, and descale every month or two if your water is hard. In hard-water areas, a lot of the odd flavours and most of the breakdowns start here.
7 · Keeping it in the fridge
The most widespread belief of the lot. The fridge is a poor choice for two reasons: every time you take the container out, the cold coffee condenses moisture from the air, and it absorbs odours with notable ease.
Fix: a closed cupboard away from heat, in the original bag with its valve. And if you've bought more than you'll drink in a month, the freezer genuinely works — in small portions, and never refreezing what you've thawed. It's explained in the storage guide.
Where to start
If you're only going to fix one thing, make it the first: freshly roasted coffee. It's the one that changes the result most and the only one that doesn't require buying anything new.
After that, the grinder. With those two you'll be ahead of most people. If you use a moka pot, the specifics are in coffee for a moka pot. Coffee is in the shop, and if you want it always to arrive inside the good window, that's precisely the point of a subscription.
