We are lucky enough to have access to some 5 year old whole Pacific Gem and Motueka hops. While aged hops are generally shunned due to their “cheesy” character, traditional Belgos do use aged hops for their sours. In general, bitterness and sour are opposing forces, so sour beer brewers do not want much bitterness at all. Anything over about 5 BUs also starts to inhibit lactobacillus growth, something sour brewers want.
The hoppy solution someone stumbled upon after too many Chimays is aged hops. As we know, hops have a handful of really important organic acids, grouped into the clades of alpha and beta acids. Nether are soluble in wort. However, alpha acids can be converted to iso-alpha acids at high temperatures. Isos are soluble in wort, and give bitterness to the beer. Beta acids are not soluble and do not undergo isomerisation.
Both alpha and beta acids can be oxidised. Alphas become humulinones and betas become hulupulones. Easy. The killer thing is that both these guys are soluble and give a smoother bitterness than isos. While humulinones don’t survive boiling, but are great in a dry hop, hulupulones survive wort production and fermentation. They don’t affect lacto growth, and they provide a super smooth, pleasing bitterness.
Hulupulones form slowly in aged hops, and are more prevalent in pallets than cones. Yeah sure, we are using cones, but for 5 year old hops beggars can’t be choosers.
Hope all your humulones become iso-adhumulone and your lupulones become hulupulones until your hearts content.