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The other day I was drinking Half Acre's Imperial IPA, Double Daisy Cutter, and the hop aroma was absolutely fantastic. Closing my eyes and taking a sniff, I could almost imagine that I was standing in the middle of a hop field just before the harvest. As a homebrewer, you get this experience more than most people. Opening a sealed package of hops from the homebrew store gives a blast of that fresh aroma that sometimes seems to be difficult to capture in a beer. The truth is, the simple technique of dry hopping is all it takes to bring out those wonderfully fresh citrus, pine and earthy aromas in your homebrew.
Traditional boiling changes the natural alpha acids in hops into iso-alpha acids—they're the stable compound that provides the bitter flavors in beer. Unfortunately, boiling also breaks down the volatile essential oils that comprise the aromas and much of the flavor of the hop itself. When we first talked about hops, I mentioned that the later the hops are added to the boil, the more they will affect flavor and aroma. This is because the less time hops are boiled, the fewer bitter iso-alpha acids are produced and the fewer aromatic essential oils are driven away. Dry hopping is basically the ultimate late hop addition.
The phrase is a bit of a misnomer, since you don't keep the hops dry at all. Instead they are added to the beer in the conditioning phase, after the fermentation but before it's time to bottle. Usually this means you'll add the hops after the airlock has stopped bubbling. If you're doing a two-stage fermentation, then the dry hops would be added at the time you transfer your beer to a secondary fermentation vessel. Otherwise the rapid discharge of carbon dioxide will "scrub" the delicate flavors that we're trying to preserve. Since the beer is only around 65°F at this point in the process, the breakdown of essential oils occurs much more slowly, preserving the flavor and aromas of the hops.
Dry hopping is a great way to experiment with different recipes. You can always dry hop a Pale Ale or an IPA with the same variety of hops used in the recipe. Or you can try to find a variety that complements the flavors you're already using. In our Pale Ale, for example, dry hopping with the citrusy Amarillo hops would help bring out the grapefruit character of the Cascades added late in the boil. But you can also try dry hopping other, more unexpected styles to make a hoppy American-style Stout or a hoppy wheat beer.
When you do dry hop a homebrew, you'll want to drink it a little quicker than usual. The added aromas are still quite volatile, even at cooler temperatures, and they will dissipate within a few months of bottling. Some lasting flavors and aromas will remain after that, but you will notice that the first few bottles you open will have a much stronger aroma than the last ones in the batch.
Dry Hopping Instructions
The only equipment needed is a nylon hop bag, a few clean glass marbles, and about an ounce of hops. The job of the marbles is to sink the bag of hops to the bottom of the carboy or fermentation bucket. You can use as much as two ounces of hops for a five gallon batch, but one is enough to get the job done.
Sanitation is still important here, but since we add the hops after fermentation is complete, the alcohol present in the beer provides some protection against unwanted bacteria. Simply boil the hop bag and the marbles for about 10 minutes to sanitize. Hops are naturally antiseptic, which is one of the reasons they're used in the brewing process to begin with, so there is no reason to sanitize them. Now, just add the marbles and the hops to the bag, and put them in the fermentation vessel.
The majority of the benefits will occur within a week, but you can leave the dry hops in the fermenting vessel up to two weeks if you would like. After that, just transfer to a bottling bucket and bottle as usual.
Have you tried dry hopping your homebrew?