Tannins are naturally occurring compounds (also called polyphenols) found in many plants, including grapes, woods, and teas. With regards to grapes, tannins are produced in the skins.
Red wines contain much higher amounts of tannins than white wines. This is due to three primary reasons:
1. Red wine grapes contain higher levels of tannins in their skins than do white wine grapes.
2. During the red wine fermentation process, skins are left on the grape to ferment with the rest of the grape, causing more tannins to be released from the grape skins into the red wine.
3. Following fermentation, red wines are matured in oak barrels. During this process, additional tannins from the oak are released into the wine.
Tannins are believed to contain potent antioxidants, capable of lowering cholesterol and blood pressure levels, along with many other health-related benefits.
Some people have a serious sensitivity – even an allergy – to tannins. For some, consuming tannins can lead to a migraine headache.