Ok, so what about aroma and flavor? Hops have a broad range of flavors and aromas: some are woody and earthy, others citrusy, others herbal, and yet others are tropical, and this only covers a small set of flavors and aromas found in hops. The compounds that yield these properties are found in the lupulin glands of a hop cone (the little yellow blobs in the picture below). As a side note, alpha acids are also contained in lupulin glands. The compounds providing flavor and aroma are particularly volatile, though, and the longer they are boiled the less impact they have on the ultimate flavor of the beer. In this sense there is a trade off when adding hops to boiling wort: add them earlier and you'll end up with more bitterness but not much flavor or aroma, add them later and you'll get a lot of flavor and aroma but not much bitterness.
- Dry hopping: this involves adding hops into a fermenter that contains beer, an environment that is cold relative to the boil kettle. That lower temperature helps extract and preserve a lot of aromatics found in hops.
- Wet hopping: despite the name, wet hopping is not the opposite of dry hopping. Instead, a "wet hop" beer is one that was made with freshly picked hops. Lost Rhino's Hop Shove-It is a wet-hop ale--less than 24 hours after picking hops down in Madison County we used those same hops in the brewing process. (Side note: Hop Shove-It is also a dry hopped beer. Some of the hops we picked were dried to preserve them and then added to the fermenter full of beer towards the end of fermentation.)
- Hop back: a hop back is a piece of equipment that allows for extremely short mingling of hops and hot wort. The short duration of exposure means that more aromatics are preserved. Lost Rhino has a hop back and it is used in the preparation of wort for Face Plant (it was also used for the upcoming Tuppers collaboration beer).
Finally, a word of warning about IBUs: they must be taken in context. Just because two beers have the same number of IBUs does not mean they will be identical in bitterness. For example, whereas a pale ale (a style of beer that is fairly low in alcohol) with 50 IBUs will be fairly bitter, a barley wine (a style of beer that is fairly high in alcohol) will not seem overly bitter with only 50 IBUs--and may not seem bitter at all. The difference here is the initial level of sugars in the wort that will become beer: there is a lot more sugar in barley wine wort than in pale ale wort. For this reason, some brewers prefer to think about bitterness as a ratio relative to the initial sugar level of the wort that will be fermented into beer.