Why does tea get bitter after steeping for too long?

I think you can tell a lot about someone by their morning beverage. For instance, I drink coffee and Ben drinks tea. Coffee drinkers (like me) are usually more exciting, energetic, interested in the finer things in life, like to feel uncomfortably anxious, and are generally sweaty. Tea drinkers, (like Ben), are mellow, think they are Asian, feel superior since they don't "need" a lot of caffeine, like to sit around and discuss different teas, and are substantially less sweaty. Today's question is about tea, and specifically why it gets nasty and bitter after steeping too long. 


Ben? 

The answer is tannins.  Tannins are bitter-tasting compounds that are found in many plant-based products.  In wine, for example, tannins are responsible for leaving the "dry" feeling in your mouth (as far as the undertones of boysenberry and lamb shank with hints of peanut butter, beechwood, and quartz, I have no idea what causes those flavors).

Most tannins are water soluble so the longer that plant material sits in water, especially hot water (tea), the more tannins will be dissolved into the water.  Beer brewers also spend a lot of effort keeping tannins out of their beer by making sure that they remove all of the grains before the boil and by removing as much left over grain sediment as possible before the long fermentation process.