Reason 1: Brewing the Coffee for Too Long
The first place to look if your coffee is tasting bitter is at how long the extraction or pour time is, as you just might be taking too long over it. Coffee gets its flavour from the chemical reaction of the beans with hot water, but overexposure will result in that sour taste we want to avoid at all costs. Many novice coffee-makers try to extract too much coffee from each dose resulting in a very light blonde colour liquid coming from the machine at the end of the shot. To rectify this, stop the pour the second you see the liquid turning this colour.
Reason 2: The Water is Too Hot
Boiling the water to 100 degrees Celsius and then pouring over the coffee may seem like the right thing do, however the reality is that’s slightly too hot and may be the cause or at least a contributor to your burnt-tasting coffee. The optimum temperature is actually anywhere from 90 to 96 degrees so keep this in mind to reduce the likelihood of a bitter brew.
Reason 3: Dirty Equipment
This one may seem obvious, but you’d be surprised at how often this is the culprit of sour-tasting coffee! Residue left over from previous cups of coffee can create a stale taste in the current cup. Clean your coffee machine regularly to ensure each cup is as fresh and tasty as the last. Industrial machines will require cleaning at different intervals to home machines so check with the manufacturer guidelines for your individual piece of equipment.
Reason 4: Grind Size
One other big reason your coffee is tasting off is due to the size you’re grinding your beans, as this affects how the flavour compounds, within the beans themselves, dissolve. If the grinds are too big it can lead to under-extraction of the flavours resulting in a sour taste while if the grind size is too small the opposite can occur, too much flavour is taken from the beans creating an overly strong and
bitter taste. A little trial and error are needed for this one as different machines and brewing methods will lean towards different grind sizes, but if your coffee is bitter now the chances are the grind is too small!