Oude Geuze Boon is an unflavored lambic made in the old style. Oude Geuze Boon is a blend of mild lambic matured for 18 months (90%), strong three-year-old lambic (5%) and young lambic that allows a second fermentation (5%). The second fermentation takes place in the bottles and this creates the champagne-like bubbliness characteristic of geuze. It is this second fermentation in the bottles that makes lambic geuze.