Overly Bitter or Clinging Bitterness in your Beer
Well, overly bitter beer indicates that too many alpha acid units were add to the boil. That would be 20, 40, 60 or more minutes in the boil. Always add bittering hops based on alpha acid units rather than ounces. The alpha acids are forever changing.
Now if the bitterness is clinging, this could be caused by high levels of sulfate ions in the water. The addition of Calcium Sulfate (Gypsum), Magnesium Sulfate or Water Salts to the wort could be the cause of lingering bitterness. If the sulfate levels are above 50 PPM they begin to have a significant effect on perceived bitterness especially in the finished beer.
In some beer styles, like a Bohemian Pilsner, Oktoberfest and Munich Dunkel, the sulfate level is quite low and the beers have a malty presentation. These styles were originally produced because the sulfate level of the water in Pilsen is around 5 PPM and 10 PPM in Munich. In these beer styles sulfate levels over 15 PPM can be too high.
Contrast that with Burton which has an average sulfate level of 450 PPM along with a high level of Magnesium, 40 PPM. The resulting beer styles from this region are dry accentuating the hoppiness of English Bitters and Pale Ales.
If you are not adding sulfate to your wort and are perceiving the lingering bitterness, check with your local water source and ask for a copy of the latest water analysis. WaterOne brewers can just check the homebrewing section of their website.