Brewing coffee is all about extracting good tasting stuff from ground coffee beans - some factors which affect extraction include: Water temperature (hotter

Brewing coffee is all about extracting good tasting stuff from ground coffee beans - some factors which affect extraction include: Water temperature (hotter water => more extraction) Grind size (finer grind => more extraction) Brew time (longer time => more extraction) Overextracted coffee tends to taste bitter (or, as many people say when they're used to bad coffee, "like coffee" :)) and underextracted tends to taste sour. A bad grinder won't give you a uniform result (some will be more coarse, some will be more fine). Brewing should match up an appropriate water temperature + brew time with your grind size, but if your grind isn't uniform the coarser stuff will underextract and the finer stuff will overextract. So your coffee can end up having both sour/bitter flavor if the grind isn't even.