What do we look for in terms of taste in a filter coffee?

A complex cup and a balance between acidity and sweetness. To achieve this, start by using a fixed ratio and temperature and play with the grind size of the coffee. With an electric grinder, choose a setting that suits the filter. With a manual grinder, start by setting the grinder to 0 (when the wheels are fully tightened and the handle does not move). Then loosen the wheels by counting the clicks, this number will be your starting setting (this depends totally on the type of grinder you are using). Prepare your filter, note the extraction time and taste it. If it is under-extracted, the beverage will be too acidic, lacking in flavour and watery. This means that your grind size was too coarse and the water passed through the coffee too quickly. You should therefore grind more finely by adjusting your grinder accordingly. On the other hand, if it is over-extracted, the drink will be bitter with a bad aftertaste. In this case, you will have to grind more coarsely so that the water can flow through the coffee a little faster. For each coffee, it is a matter of brewing, tasting and repeating until you reach the desired cup.