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What exactly is acidity in coffee?

Acidity – a mouth-puckering effect. Sour rather than bitter, imagine sucking a slightly sour orange or a sweet lemon. Think sharp and tangy. Acidity is a dry and somewhat sparkling element of coffee made from superior coffee beans and is a desirable flavour. Described perhaps as a pleasant sharpness which is usually picked up first as the coffee hits the taste receptors toward the front of one’s tongue.

While this might be an acquired state for coffee novices, this acidity often differentiates a good quality coffee from the lower-grown and somewhat cheaper varieties.  

Bitterness is an unpleasant flavour element which is picked up only on the back of the tongue and as an aftertaste. There is a fine balance between acidity and bitterness, some times this is hard to differentiate. The sweet/sour balance of a Seville orange or a chocolate bar with 80% cocoa is sought after. A roaster cannot make coffee bitter but a barista certainly can. The cause is usually one or more of the following:

Bitterness, acidity and coffee flavour

Acidity, along with aroma, aftertaste, sweetness and body or mouthfeel, is a desirable flavour sensation. In addition to the front of the tongue, a hint of bitterness (but not too much) can also be picked up at the back of the tongue. The first thing I look for when tasting is bright or lively acidity. At the same time, I look for the hidden or more subtle sweetness which comes through,  either while drawing the coffee through the crema or hidden quietly in the rich brown liquid itself.  

The level of acidity is too high if it is unpleasantly sour or if it causes you to physically pucker. A high or good acidity is described as a sharp sensation as compared to a smooth or characterless coffee.

1. The coffee has sat for too long in a pot or even your French press (plunger).
2. The water you used was boiling compared to just off the boil. The thermostat in a traditional espresso machine or bean-to-cup machine was set too high.
3. Dirty equipment where remnants of old coffee are affecting the flavour.  
4. Coffee that is too coarsely ground can result in weak or poorly extracted coffee. This also reduces the acidity and results in a flavourless or characterless coffee. If the coffee is too finely ground, the level of bitterness will rise. Find the balance.
5. Pulling too much water through the coffee. Something is wrong if it takes more than 30 seconds to pull your shot! This applies particularly to traditional espresso machines when baristas pull more than either 30 ml or 60 ml for a single or double shot of espresso. For an Americano, DO NOT pull more water through the puck; use another water source, please!