When they are young they are the rough almost tactile sensation in the mouth. The harsh ones are from the seed and stems. The softer tannins are from oak. Leather flavors in aged red wine is are to be expected. TANnin is used to TAN leather, so the smell is from the tannins.
Leather tends to be more pronounced once the fruit has faded.
Tobacco - along with cedar and leather a product of well aged tannins. Different than tannins, this is the drying out of the mouth. It is due to the acidity in general. Wet horse blanket - Brett, a common bacterial spoilage, in smaller concentrations it is more like dirt than merde. Strawberries, bananas and raspberries, as well as a cotton candy sweetness in the nose, are typical.