Hertog Jan's Proeftuin #15 is an experimental tripel born from their Tripel Hop Bitter Fruit recipe, aged for six months in lightly toasted bourbon barrels immediately after brewing. Part of the brewery's Proeftuin series—a rotating selection of limited specials for members—this barrel-aged expression shows darker colour than a typical tripel, with smooth texture and deepened fruit character from the wood. Hop bitterness persists in the finish but is more restrained than the unaged base beer, with warming alcohol and subtle sweetness from the bourbon contact.