The whole drip brewing process relies on hot water coming into contact with coffee grounds and then dripping through to a receptacle of some sort – a mug perhaps. If the water passes through quickly, you’ll end up with weak coffee. If it goes through slowly, you might get bitter coffee (similar to over-extraction on espresso makers).
The grind size you use for drip coffee will depend not so much on the brewing method you choose but on the type of filter you use. Filters come in all sorts of shapes and sizes and are made from many different materials: glass, nylon, paper, plastic, and metal. If you don’t use the right size of grind for your filter, it will clog up or, worse, you’ll end up with sludge instead of coffee.
So, how can you tell? Simply check the size of the holes in your filter. Plastic and metal filter tend to have large holes so would take coarsely ground coffee. Medium-holed filters would take a medium grind, while small-holed filters will take a fine grind. Be careful with this one though, because if the holes are too small, the fine grind will clog them. Better use a medium grind. Which is what you should use with Tecnora’s Caffemio TCM 206 as comes with a permanent nylon mesh filter.
Most automatic drip coffee-makers using paper filters will take a medium grind. But even with paper filters, there’s a choice. Drip coffee makers come in two types: those with flat-bottomed filters and those with cone-shaped filters. And the difference? Well, it’s a matter of contact. With cone-shaped filters, the layer of coffee grounds is deeper that in a flat-bottomed filter so the water is in contact with the grounds for longer. This makes for a stronger cup of coffee.
It all comes down to choice – and the type of filter your machine takes.