Smaller berries = better skin to fruit ratio = more tannin.(Warmer years 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 opportunity. Down the road . https://cyan-lark-kbzsw4.mystrikingly.com/blog/tuy-nhien-co-nh-ng-b-c-bi-m-t-d-th-c-hi-n-nen-r-u-brand-name-danh-gia