Polyphenols are an antioxidant that organic grapes produce to protect against fungi, bacteria, frost, and other negative influences. They also affect you in a similar way, helping to fight many toxins in your body.
Polyphenols are abundant in our wines for many reasons. The main one is, when grapes are sprayed with chemicals, it often removes the need for the plant to produce polyphenols as defense.
Fun fact: Since polyphenols are found in grape skins, darker wines will often contain more (darker wines means more contact with the skins, imparting that color).
We wrote a quick guide to polyphenols on our sister site, A Matter of Taste. Check it out here!