© 2021, Randy Mosher / Craft Beer & Brewing Magazine
Above: It takes two to tango. Never underrate the contribution of hops’ crucial counterpart: barley malt.
IPAs currently account for about half of all craft beers sold in the US. Their bold flavors and shape-shifting characters, plus the fun of terroir and varietal characteristics make them endlessly fascinating. Like most beers, they’re mostly malt, hops, water and yeast, but obviously the hops are the starring attraction.
But no matter how hoppy the beer, more than 98 percent of the dry ingredients are typically malt or other grains. It’s crucial to have that malty counterbalance to the bitter, herbal character of hops. Together, they’re perfect—as we’ve generally agreed for the last thousand years or so.
To understand IPA today requires a review of the last 40 years of its evolution. Early craft ales, IPAs included, employed plenty of crystal/caramel malt, transplanted from early homebrews where it compensated for the diminished aroma of the malt extracts used. Flavors range from a light kettle-corn caramelization to toffee and burnt sugar notes. Those used in IPAs stick to the lighter half of the spectrum and typically show caramel or toffee notes, making the beer a bit heavy on the palate. Taste Sierra Nevada Pale Ale and you’ll get the picture.
Over the last 20 years there’s been less of this, allowing the delicate flavors of hops to shine through. Many modern IPAs use no crystal malt at all. One problem is that it ages rather poorly, picking up a characteristic leathery-oxidized flavor from compounds like 2-isobutyl quinoline. This effect seems to be strongest in mid-colored malts at about 40 Lovibond (80 EBC).
The historic base of IPA remains pale ale malt. At 2 to 4 Lovibond (4–8 EBC), it makes a gorgeous pale amber beer. Extra color comes with a bolder aroma: a brisk nuttiness resulting from kilning under low moisture conditions, bolstering its refreshingly dry qualities. So, pale ale malt is increasingly blended down with paler lager malt or avoided entirely in the newer hazy/juicy style, where smooth and fat are the goals. Other malts, however, have useful flavor notes: spun sugar from crystal-10 (20 EBC) and confectionary caramel from Vienna malt or caramel-20 (40 EBC) being the most useful.
Adjuncts were never abundant in IPAs until the recent wave of hazys, where grains such as flaked oats, wheat and rye can make up of half of fermentables, mostly adding creamy texture, the exception being the sugar’n’spice notes of rye. Because of its gluey nature, it maxes out at 30% of the grist.
The original IPA hops were landrace varieties, spontaneously developed and carefully nurtured for centuries, the most famous of which was East Kent Goldings. Contemporary brewing texts always make a point of saying that the best hops are mandatory for IPAs. In fact the famous “October” beer that was IPA’s forerunner took that one step further, using recently harvested hops, which as we all know, taste freshest.
While East Kent Goldings still make marvelous beer, it’s an understatement to say that a lot has happened in the hop world in the last 200 years. Accelerating in the last few decades, we are now faced with a kaleidoscope of new varieties, tasting of everything from strawberries (Barbe Rouge) to white wine (Nelson Sauvin, Hallertau Blanc) to tropical punch (Galaxy and many NZ varieties). The choices can be overwhelming, and unless you just want to go by what is popular with others, require a brewer to really dig in and try to understand the personality of each variety.
Hop aromas have always been difficult to get a grip on. There is, in fact, a longstanding term in hop parlance—spicy—that has no relationship to any identifiable spice, but is a code word for hoppiness itself. Saaz hops, a variety to which this label is often affixed, represents this best. As long as we all know what we’re talking about, it’s an OK word, but it highlights the inadequacy of descriptive language, even among experts.
One of the reasons hops are challenging to describe is the vastness of their aromatic composition. Called by one source one of the most aromatically complex of all herbs, hops contain hundreds of identifiable odorous chemicals at varying levels, depending on variety, location/terroir, growing conditions, age, storage conditions and more. Brewing and fermentation specifics create further changes. Unlike malt, whose flavor spectrum can be perfectly tracked by terms for various cooked, baked and roasted foods, hop aromas don’t track anything so familiar. As a result, we’re literally at a loss for words. While we can learn the names of a few of these odor chemicals, most have only a passing similarity to things we know well.
The majority of key hop aroma compounds are terpenoids. If you think about the word “turpentine,” from which it is derived, you’ll get the picture. They have sharp, oily, resiny aromas spanning a range from the piney through floral of all sorts to delicate citrus. They’re abundant in the plant world; we pick and choose from that as best we can for our vocabulary.
While many terpenoids are present in hoppy beers, a few are particularly prominent and are worth getting to know. Here are a few, with aroma descriptors from GoodScents Company, an online aroma chemical resource:
Geraniol: sweet floral fruity rose waxy citrus
Linalool: citrus floral sweet bois de rose (rosewood) woody green blueberry
Beta-citronellol: floral leather waxy rose bud citrus
Nerol: sweet natural neroli (orange blossom) citrus magnolia
To this I would add a few notes. Geraniol is prominent in all the “C-hops” (Cascade, etc.), and in my mind best corresponds to marigolds or geraniums. Linalool can be found in orange, lavender and prominently in coriander seed. Beta-citronellol smells of lemongrass to me.
Many of these terpenoids are so closely related they can change into one another under certain conditions, especially in fermentation. Nerol and linalool are isomers of each other, as are geraniol and alpha-terpineol. Since isomers are molecules containing the same number and type of atoms, all that is required is rearrangement. This is the phenomenon called “biotransformation” that is well-known in the double dry-hopped hazy IPAs, where actively fermenting yeast transforms the less desirable pungent floral notes of geraniol into the pleasing citrusy floral linalool and sometimes even into beta-citronellol. Interestingly, the latter is present in beer, but is absent from hops, so a transformative pathway is its only route into beer. All of these have been found to undergo chemical transformations in acidic media like beer over time—one reason, perhaps, for the loss of flavor as hoppy beer ages.
Many terpenoids form complexes called glycosides: small aromatic molecules bound to heavier sugar molecules. This makes them non-volatile and therefore unsmellable. As much as 21–36% linalool, for example, is bound; some may be released by thermal or enzymatic means during fermentation, but much remains in the beer. Crucially, the enzymes in our saliva and from bacteria in our mouths can break these bonds and liberate fresh aroma compounds. This is one of many good reasons to pay attention to the retronasal smell: the odors passing up from your gullet and exiting through your nose.
Some other chemical groups contribute to hop aromas. Aldehydes like (Z)-4-hexenal contribute to the green aroma of fresh hops. Some esters contribute subtle fruity notes; many are closely related to geraniol. A couple of carotenoids are important: beta-ionone brings violet or iris root floral notes; beta damascenone is associated with overaged hoppy beers, presenting a foxy concord grape or applesauce odor. Carboxylic acids like the cheesy-smelling isovaleric acid usually result from improper storage.
One important group of aroma-active hop compounds contains sulfur. Smellable in vanishingly small amounts, our exquisite sensitivity to sulfides and thiols is due to copper and zinc complexes in certain of our olfactory receptors. Hop companies have had to purchase much more sensitive analytical equipment just to study them. Despite low parts-per-billion concentrations, they play an outsize role, especially in the newer fruity and tropically-tinged varieties. With long, unwieldy names, they are usually just abbreviated. 4-MMP (4-mercapto-4-methylpentan-2-one) is perhaps the best known, with a fruity/blackcurrant character. Others are responsible for sauvignon blanc/passionfruit and latex/guava notes. Thiols with oniony off-flavors are created by hop plants in response to stressful growing conditions. “Onion bagel” is an apt description for these toasty notes.
Aside from the challenge of learning dozens of different hop compounds, an odor is never the simple sum of its parts. Odorants may positively stimulate sensory receptors but can also inhibit them. They also compete with each other for receptor binding spots, and the most competitive odorants are not necessarily the ones stimulating the strongest sensation. Many terpenoids are well-known masking agents. So, the pattern ultimately presented to our nose for decoding is anything but logical. This is a problem, but for clever brewers, there is the possibility of finding magical combinations that are much more than the sum of their parts.
So that’s the biochemistry of hop aromas. Now let’s look at it from the viewpoint of our nose and the vocabulary we can actually work with. This is manifested in tools like aroma wheels and spider diagrams that can serve as vocabulary prompts. Here is one I put together based on descriptors I think most beer enthusiasts are interested in and are familiar with. However, there are a million ways to slice and dice the experience. In addition to functioning as a flavor wheel, these spider charts can be used for visual note-taking by placing a dot for each attribute, with higher values placed further from the center. Connecting the dots gives a recognizable pattern, which is why they now are often included as part of hop varietal information provided by hop companies.
You can’t make IPA without yeast, but its effects on the beer are far outshone by the depth and complexity of the hops. The effects of yeast are subtle; more push and pull, affecting the total pattern without revealing itself too much. Certainly, there are classic yeasts associated with British ales possessing specific characteristics. Brewers of hazys appreciate yeasts that enhance the creaminess of the beers and engage in biotransformation.
It’s easy to focus on the conspicuous aspects of IPAs, which are their bold flavors and bright aromas. But a true revelation, for brewers and enthusiasts alike, requires peering beneath the surface into their beckoning depths.