How do hops work? It seems like a rather innocuous question. You'll be sorry you asked.
On Wednesday, we discussed what hops do; we mentioned that while hops originally served a purely preservative function (mash hopping was very popular for this where the bitterness is more subdued), these days they are used more to define the flavor of a beer. It's taken almost a hundred years to figure out exactly how hops work, but it is, literally, down to a science; the number and variety of hop strains being used in all sorts of applications is one of the driving, and defining, forces of the American craft beer movement.
The question then is, how do hops impart their bitterness and/or aroma? Hops can be broken down into two parts: vegetal matter and lupulin glands. The vegetal matter is the green stuff. The lupulin glands are the yellow stuff.
Vegetal matter is the green, leafy part of the hop. It constitutes over 85% of the hop components, yet it is the least useful portion of the hop. While the leaf itself contributes something in the way of tannin and protein, these effects are mostly negligible. In fact, even considering all of the useful parts of the hop, an efficient brewery will effectively utilize less than 10% of the weight of a hop. In short, it's the lupulin glands that are the stars of the hop show.
What the heck are lupulin glands?
Glands filled with lupulin. Duh. The easy answer is that lupulin and the lupulin glands are the yellow stuff you see on the picture to the left there. It contains the stuff that makes your beer bitter and smell nice. For our purposes, we can break these down into three more technical components: soft resin, essential oils, other stuff. The soft resins themselves are comprised of alpha acids and beta acids. The alpha acids are rendered out of the hop by the boiling process. You will almost always see an alpha acid number associated with a hop profile; the Hop Union Data Book says that their strain of US Cascade is 4.5-7.0% Alpha Acid. This means that 4.5-7.0% of the hop (remember 85% of it is vegetable matter) contains usable alpha acid. On the other hand, Beta Acids are not affected by boiling, but some additional bitterness imparted by oxidation (exposure to air), thus the bitterness is more prevalent in the aroma; the data sheet shows that US Cascades are 4.5-7.0% Beta Acid as well (this matching is coincidental, if you were to look up US Centennials you would see 9.5-11.5% Alpha Acid and 3.5-4.5% Beta Acid).
So what do these numbers mean? Well, the higher the number the more of that resource the hop has to impart the desired characteristic. So, as a general matter, more alpha acid means more bitterness; more beta acid means more aroma.
There are also essential oils trapped in the lupulin. These oils contribute to the particular aroma that are taken out of the hop. While people smarter than me have taken a shot at quantifying what a hop aroma would be based on numbers (i.e., like with alpha acid and beta acid), the fact is it is hard to tell just looking at numbers and oil types what a hop will smell like. It's best to just get one of the little buggers in your hands, roll it around a bit and take a big ol' whif.
We'd be remiss if we didn't mention the classification of "Noble Hops." These are a classification of hops that are grown in Europe (Germany and Czech Republic mostly). They are low-bittering, high-aroma hops. Interestingly, they are Eurpoean Appelations of Origin, meaning that only those grown in the location given in the name of the hop may be called that (e.g., only hops grown in the Saaz region of the Czech Republic can be called "Saaz").
Finally, on Wednesday we failed to mention another hopping technique called the "hop back" where the wort is run through a bed of hops on its way to the chiller. This technique is simply another method of aroma hopping.
Even after all of that, these "fresh hop" beers brag about their usage of whole, fresh hops in the brewing process - "using fresh hops is a big endeavor, as the process requires four to five times the volume of hops compared to the normal process of using pelletized hops" - the fact is, using the hop in whole leaf form is the least efficient means of exploiting it. Like driving a Hummer when gas is over $3.00 a gallon, making a "fresh hop" beer in the midst of a hop shortage seems a little irresponsible.
Of course, this week we've got the 1967 Cadillac El Dorado convertable, hot pink with whale skin hubcaps, all leather cow interior and big brown baby seal eyes for headlights! Yeah! And we're driving around at 115 mph, getting 1 mile per gallon, suckin' down whole leaf hops like they're going out of style in a non-biodegradable styrofoam container. And when we're done suckin down those hop-bombs, we're gonna wipe our mouths with the American flag. (apologies to Denis Leary for the abuse of his song; also: just to make it clear: we do not endorse driving hot pink cars either during or after drinking hop-bombs)
Great Divide Fresh Hop Pale Ale (BA.RB.)
Appearance: Gold and bubbly with a huge creamy white head; none of the floaties of the heavy handed, but nice bubbling from the carbonation
Aroma: You can smell this thing from across the room; fruity and floral; the malt aromas are buried under the hoppy brightness, but it adds some bottom-notes the hop high-notes
Flavor: bitter and grassy, with a solid caramel maltiness that gives way to a lingering finish of alcohol and sharp fruitiness; a slight spiciness pervades
Body: medium-light body that goes down very easily with a lingering finish
Drinkability: perhaps the most drinkable of the three that we had this week; the light body provides a surprising maltiness
Summary: tipped towards the hoppy side, it is still a fairly well-balanced beer;
we were having a discussion this week about expectations for this type of beer - one of us took the side that these beers are supposed to be hop bombs, malt is there because it has to be, but it is definitely the back-seat, the hops are the showcase; the other of us took the position that despite the obvious emphasis on hops, there needs to be some malt backbone to provide at least a little relief and complexity aside from the hop bombardment which tend to be one note (cascade/centennial); so the question to you: do you look for a malt component in your hoppy beers?