It's hip to know your hops

"Hops are to beer what grapes are to wine," Samuel Adams maker Jim Koch has claimed in a series of print and TV ads. They are the "soul" of beer, he asserts.

Everyone knows what grapes are. But can you visualize a hop? Hops come from a perennial vine that can climb 20 feet or higher. As summer wears on, clusters of tiny blossoms give way to greenish-yellow cones about 1 to 2 inches in length, which are harvested in August and September.

Hops are a seasoning, like salt. They make up far less than 1 percent of the volume of the typical American lager, but they have several important functions: Their bitterness balances the cloying sweetness of the malt, they add a pleasing aroma and they retard the growth of microorganisms.

There are dozens of hop strains, from coarse, bittering varieties to delicate aroma hops. "Noble" hops from Central Europe have a subtle spiciness that's prized in lagers.

English ale hops are noted for their woody, earthy overtones.

Pacific Northwest strains such as Cascade, Chinook and Centennial have intense, in-your-face fragrances often summed up as piney, resiny and citrusy. "Grapefruit" is another common descriptor.

Chemicals called alpha acids are the primary source of bitterness in hops. Brewers measure the intensity using international bitterness units, or IBUs. Budweiser clocks in at a minimal 10 to 12 IBUs; Sierra Nevada Pale Ale has 37 IBUs; some imperial India pale ales claim levels of 100 IBUs or more.

Rather than bludgeon taste buds with bitterness, some brewers are taking a different approach with hop harvest ales, also known as fresh-hop or wet-hop beers. These beers are brewed with hop cones rushed from the vine straight to the brewkettle, without the customary kilning or compressing into pellets. Fresh-hop ales have a complex perfume from the volatile hop oils and a lightly grassy, herbal taste.