Can't remember where I got this from but it's a thought anyway...
Description: Think of the sensation you get in your mouth when sucking on a teabag, or chewing on grape skins (Yeah, I know, not stuff you do every day). Sometimes confused with bitterness. Astringency is a dry mouth-puckering sensation, whereas bitterness is detected on the back of the tongue and is desired and assertively noticeable in certain styles, such India Pale Ale or American Pale Ale.
Cause: Several causes. Extract brewers sometimes have problems with astringency from steeping their steeping grains too long, or at too hot of a temperature. Overcrushing your grain, oversparging or sparging with boiling-hot or alkaline water, and bacterial infection. Excessive oxidation also produces a rather unpleasant astringency.
Remedy:Pay more attention to water temperature whether mashing, sparging, or steeping. Keep good sanitation practices. Make sure grain is crushed, not pulverized into powder. Try to minimize oxygen exposure after fermentation to decrease chance of severe oxidation