Smaller berries = better skin to fruit ratio = more tannin.(Warmer years cater to produce small berries.) Petit Verdot and Cabernet Sauvignon have a thick skin and can extract a tannins. Wine Tasting is fun so do not make it a complicated, scientific endeavor. https://www.Google.com.gi/url?q=https://www.folkd.com/submit/ruoutaychinhhang.com/chivas-18.html/