As you sip that IPA, have you ever pondered what it is about the bracing bitterness that inspires such passion? People may like malt, but they love hops, sometimes beyond all reason. It verges on sickness, in the most glorious way, most certainly an obsession.
From the earliest days of beer, bitter herbs have being used to balance sweet malt, add to its refreshing qualities and lend a sharp substantial weight to the drink. Historically, bitterness in beer comes and goes in waves, and, boy, are we ever riding a crest right now. Might be time to peel back the layers on beer’s most magical flavor.
With just a few exceptions, bitter tastes play secondary roles in cuisine, making beer really stand apart from most other foods and drinks. It is an acquired taste, clearly evident as we watch our friends journeying into craft beer. There is a good reason for their hesitance. Bitterness is a signal to be on the lookout for something poisonous.
Our chemical senses exist to give us information about materials in the environment—especially potential food—to help us detect whether a leaf or a berry or a drop of nectar might be nourishing or dangerous. As plants and animals coevolved, they engaged in a fascinating tango, with the plants operating in full self-defense mode, sprouting such obvious deterrents as thorns and thick husks to avoid been eaten. At some point, they developed the ability to make substances toxic to their predators.
In due time, animals developed the ability to recognize poisons such as strychnine, cyanide, alkaloids and many others. Awareness by itself is useless, however. These perceptions need to be coupled to a call to action, one that was powerful, instantaneous and aversive. The sense of bitterness was born.
And so the dance went on, with plants developing ever more ingenious toxins and animals eventually evolving the ability to recognize and avoid tens of thousands of bitter chemicals. With that pattern in place, some plant species evolved a decoy that was as good as the real deal: They lost the ability to produce the toxins and began to produce perfectly harmless chemicals such as the ones found in hops that were just as effective at triggering the bitter-aversion mechanism, keeping most plant-eaters at bay.
The number of Tas2R genes, the genes that code for bitterness receptors, is highest in plant-eating animals and much lower—or absent—in pure carnivores. At present, 25 receptor genes have been identified in humans and mapped to various substances they can detect. The more genes, the more potentially toxic chemicals can be detected, although the receptors may have other purposes. Bitterness receptors have been found in the entire length of the human gut and in other non-obvious places such as the lungs. What purpose these far-flung sensors serve is mostly a mystery.
The bitterness of certain herbs and spices was well-known in ancient times, and some such as rue would likely have found their way into ancient beers. Some chemical evidence for the composition of those beverages has been found in recent years, most notably by Dr. Patrick McGovern, the archaeologist and expert on ancient fermented beverages, but because of the large overlap in the makeup of many herbs and spices, it has not been possible to find a lot of chemical evidence of their use in beer.
The earliest physical evidence for the use of hops in beer was unearthed in Umbria in Northern Italy and dated at about 900 B.C. It would be two millennia before the introduction of hops into European beer began for real. In the interim, beers were seasoned with a secret mix of herbs and spices called gruit; one component of gruit, bog myrtle (Myrica gale), has some bitterness and a pleasant resinous aroma. Wormwood and gentian, both searingly bitter, have been used occasionally in beer until recent times. Historians believe the switch to hopped beers began in Northern Germany, perhaps in the Hansa trading town of Bremen, then spread slowly along the North Sea and eventually to Amsterdam, then to Flanders, finally jumping the channel to England along with waves of immigrants in the 15th century. By about 1600, the old unhopped ale was no more.
The clean, soft bitterness of hops suits beer perfectly, at least to our modern tastes. Very recent science is suggesting that we have the ability to discriminate among five different types of bitterness. The sensation offered by cinchona bark (quinine) or wormwood is piercing and can be unpleasantly dry, very different from the mellow bitterness of hops. In addition to their preservative powers, this is likely the reason hops so completely dominate the world of beer.
Beer’s bitterness is not all about the hops, though. Dark beers contain plenty of bitterness from roasted malts. The Maillard reaction, the source of most color and flavor in beer, produces hundreds of highly aromatic chemicals that lend their characteristic malty/bready/caramelly/toasty/roasty aromas, but also yields odorless color molecules called melanoidins that can be strongly bitter in darker malts.