If you're a fan of hop-forward beer styles like IPAs, Pale Ales, and Imperial ales, you're probably not going to be interested in this post. Those styles tend to benefit from fresh hops, and as much of them as you can infuse into the beer. There are other beer styles, like Belgian ales, lambics, and others which aren't hop-forward in nature. These beers can benefit from more-subdued hops bitterness and flavor which allows their malt character to shine through. This is where aging can make a difference.
Although I'm familiar with aging wines, cellaring certain beer styles to allow them to age, and even bottle conditioning some home brews to improve the flavor, I'd never heard of aging hops. At Barley's 20th Annual Meet the Brewers event, I met brewmaster Sam Hickey of Smokehouse Brewing and Lenny Kolada (a co-owner of Smokehouse). Sam was there with his Brewtus Maximus Belgian Quadrupel (which is an absolutely excellent beer). I told Sam that I'd brewed three batches of Belgian tripel over the year and they just weren't working out to my taste. The first used UK Goldings hops and had an unusual bite to the bitterness that I didn't like. The second used the same recipe, but swapped the UK Goldings for a blend of Styrian Goldings for bitterness and Czech Saaz for flavor and aroma. That one got much closer to what I wanted, but still wasn't quite right. The third, which I just put in the fermenter a few days ago, used Northern Brewer, Stryrian, and Saaz. It also used a different combination of malts and sugars, plus sweet orange peel and coriander. When he heard my frustration at getting the bittering right, Sam suggested that I might want to look at aging the hops. I told him I'd not heard of that.
As you're probably aware, the bitter flavoring we normally associate with hops comes from the acids in the hops cones. As these acids are exposed to oxygen, they break down and lose some or most of their bittering capability. Fortunately, they retain their ability to prevent infection in the beer, which is useful in styles where the bittering isn't as important - like wheat beers, Belgian ales, and others. Aging hops takes away some of the flavor as well.
To age hops, simply leave them in a dry place like an attic for one to three years. Keeping them in a brown paper bag is a good way to keep them relatively clean during the aging process.
Aging generally requires whole leaf hops, as pellets don't age as quickly.
Hops aging can be accelerated by placing the hops in a 150-degree Fahrenheit oven for up to twelve hours. The down-side to this is that it can create a very intense aroma in the house that lingers for days.
There are some suppliers that offer aged hops. Hops Direct, for example, offers aged hops at a variety of prices in the $5-10 per pound range.
This is something I plan to experiment with. I will first need to find some whole hops in the varieties I prefer to use in my Belgian ales, then get them aging...