Cause:
Acidic coffee has an unpleasant, sour taste and happens when coffee is over-roasted or incorrectly brewed. It occurs when the ground coffee is too coarse, or the grinding level is too coarse.
Solution:
The solution is simple, adjust your grinding level to a finer setting, or purchase ground coffee that is finer. This will prevent you coffee from tasting sour and acidic.
On the other hand, if your coffee is tasting too bitter, it could be because your coffee is ground too finely. To resolve this, you need to adjust the grinding level to a coarser setting or change the type of ground coffee you are using to a coarser variety.
Ensure that you always use fresh beans, and that your coffee machine has been properly maintained, which includes cleaning and descaling.