Brewing for Flavor: Hops
The next time you open a beer, fill your glass halfway. Give the beer a good sniff; get your nose way down in there like the wine snobs do and enjoy the aroma.
Does it smell flowery? Fruity? Pine scented?
Now take a drink, just enough to fill your mouth. Consider how the beer tastes on the front of your tongue and on the back of your tongue. Is it bitter? Spicy? Grassy?
These are all qualities, both good and bad, that hops can add to beer. This versatile climbing vine, a relative of the marijuana plant, works in several ways to add widely differing characteristics to your brew.
What Is a Hop?
Brewer’s hops are the fruit or cone of the female hop plant. There are male hop plants, but most hop yards keep the males out because their flowers pollinate the female cones and result in seeds. Brewers prefer seedless hops, because seeds tend to lend harsh flavors to beer.
Hop cones contain little yellow sacs, called lupulin glands, that hold the bittering compounds and aroma constituents. Some hop varieties have high concentrations of alpha acids, the compounds that give beer its unique, bitter flavor, in their lupulin glands. These varieties are primarily used for bittering.
Hops used to add aroma to beer have high concentrations of oils and low concentrations of alpha acids. Some varieties have a bit of both and can be used for both bittering and aroma.
Hops have been associated with brewing since the eighth century, when they were first used in the Hallertau region of Germany. These beers must have tasted far better than other beers of the period, since the use of hops spread throughout the beer-brewing regions of Europe and by the 1600s were in widespread use. Even the British started using hops sometime between the 17th and 18th centuries.
Today, hops are only used by the brewing industry and a few consumer products companies that put hops in their shampoo (presumably for added flavor!).
Why Use Hops in Beer?
Hops are used in beer as both a spice and preservative. Unhopped beer tastes pretty horrid. Before hops were widely used, other spices such as nettle, coriander, and spruce were used to balance the sweetness of the malt.
The preservative action of hops is a bonus. Hops have been used for centuries to extend the shelf life of beer. The most notable example is the heavy hop rates used in traditional India pale ales. This heavy hop rate helped preserve these fine English ales during their long journey to India so the British soldiers who were busy colonizing the world could enjoy them.
Currently, hops are used mainly to provide bitterness and aroma in beer. Large breweries who wish to extend the shelf life of their products have turned to heat pasteurization. That’s because hops only prevent hop-sensitive bacteria. The bacteria that spoil beer are not generally hop sensitive.
Hop Bitterness
As beers became progressively more bland after Prohibition, large brewers were only concerned with the bittering compounds from hops. They wanted no hop aroma in their beer and wanted the bittering to be quite low. This mentality persists today and is apparent in Keystone Light, the least bitter beer in America. Luckily for connoisseurs of beer, some brewers began to put the bitterness back into the mix.
Hop bitterness is chiefly derived from the alpha acids contained in the lupulin glands. Alpha acids are generically known as humulones. Humulones make up 2 to 14 percent of the hop’s dry weight, so a hop with 5 percent alpha acids means that 5 percent of its weight is made up of humulones.
This number is taken at harvest and decreases with storage; alpha acids degrade over time, especially when improperly stored.
Alpha acids aren’t soluble in wort. However, boiling causes a chemical reaction called isomerization that transforms them into iso-alpha acids.
Iso-alpha acids are soluble, and they are what create beer’s bitterness. That’s why hop bitterness increases with boil time up to 60 to 90 minutes.
Once iso-alpha acids are in beer they add bitterness, inhibit the growth of certain bacteria, aid in foam retention and cling, and are the source for skunkiness in green- and clear-bottled beers. The skunkiness arises when light runs into an iso-alpha acid, causing it to react with sulfur, which is present in beer. The solution is to bottle your beer in brown bottles or to keep your green and clear bottles in the dark.
The other source of bitterness in hops comes from the beta acids, also known generically as lupulones. Beta acids have little significance to what brewers call “brewing value,” but their aging products do. During storage, beta acids degrade due to oxidation. Unlike alpha acids, however, their oxidation products are bitter. This means that oxidized beta acids make up some of the bittering lost by alpha-acid oxidation during storage.
Oxidized beta acids also have an aroma: cheese. This cheesy aroma is due to volatile fatty acids released from oxidized beta acids. These volatile fatty acids are identical to compounds found in aged cheeses, such as parmesan and romano.
Hop merchants are skilled at the sensory evaluation of hops and are always on the lookout for cheesy hops. This works for homebrewers too. If you smell your hops and start thinking about a big plate of linguini and marinara, snap out of it! Hops should smell like hops. If they’re cheesy, don’t use them.
Hop Aroma
It seems like many of the commercial breweries have forgotten that hops smell wonderful. Hop aroma compounds are lumped into the category known as essential oils. These oils make up 1 to 1.5 percent of the hop’s dry weight.
Although there are more than 200 essential oils found in hops and their distributions can be used to “fingerprint” a variety, only four essential oils are commonly referred to: myrcene, humulene, caryophyllene, and farnesene. These compounds are known as terpenes. Terpenes are responsible for not only the aroma of hops but the aroma of fruits, flowers, herbs, and the like. Hop terpenes are very volatile and most are lost during the kettle boil. However, some survive, especially if they are added late in the boil.
Terpenes also change during storage. These compounds change chemically (mainly due to oxidation) and become less volatile. This means that beers made from these hops with a high percentage of terpenes (essential oils) have better aroma retention. That’s one of those contradictions that keep homebrewers hopping; oxidation may improve aroma retention but will damage other hop flavors.
Terpenes lend myriad aromas to beer. Some of the common hop aromas can be described with terms such as lemon, grapefruit, fruity, woody, resinous, piney, cedary, spicy, geranium, perfumey, rose petal, and hoppy!
Hop aroma is an essential attribute of the hop, and you must be careful if you want to keep it in the wort. Late hopping, steeping (adding hops to hot wort after the boil), and dry hopping are all methods intended to add hop aroma to beer.
If you like Sierra Nevada Pale Ale, Anchor Liberty, and good German pilsners such as Bitburger, you like hop aroma. Knowing that, you probably want to work to keep some of these essential oils in your brew.
Other Hop Flavors
Besides aroma and bitterness, hops are capable of giving other characteristics to beer. These are flavors not associated with the lupulin gland. They come from the plant portion of the hop cone, the leaves.
If you start using copious amounts of hops in your brews, you will begin to extract large quantities of leaf compounds. If you’re unlucky these compounds will be detectable in the finished beer. The most common flavor attributed to hop leaves is grass. As the name implies, this smells like freshly cut grass—not exactly a fine hop nose. These beers may also be quite astringent.
The easiest way to avoid grassiness is to use low-alpha hops for aroma and not for bittering. Many brewers argue that fine aroma hop varieties are superior to other hop varieties in all aspects. Those brewers believe that the reason large breweries use high alpha varieties for bittering is to save money.
Other brewers disagree. Fine-aroma varieties produce exquisite aromas but typically have low concentrations of alpha acids. This means that if you bitter your beer with aroma hops, you’ll need to use much more to achieve the same bitterness level. When you do this, you’re adding large quantities of hop leaves that can impart grassy flavors.
While using aroma hops for bittering has drawbacks, using bittering hops for aroma purposes is fair game. The reason commercial breweries don’t normally do this is that they wouldn’t think of wasting alpha acids. Keep in mind that they don’t go after aroma too much. Craft brewers, on the other hand, have a long history of using bittering hops for aroma.
Cascade is the classic example of this practice. This variety was used solely as a bittering hop by American brewers until Fritz Maytag dry hopped his Anchor Liberty Ale with it in 1975. Thanks to the unconventional use of this hop by Anchor, the Cascade has come to symbolize many microbrewed beers.
Hop Quality
Hop quality is of utmost importance when using hops. Hop quality is affected by seasonal variations, hop packaging, hop storage, and the age of stored hops.
Seasonal variations—the differences from one harvest to the next— are documented by hop growers in “hop specifications.” These sheets contain information on the alpha acid content, total oil and the concentrations of the four principle terpenes, the aroma description, and general trade perception. Some brewers look at all of this information, while others only note the alpha-acid content for use in calculating their hopping rate.
Most of the information relates to varietal features and doesn’t change much from year to year. For example, variety X may have 1.5 percent total oil this season and 1.2 percent next season, but the distribution of the various oils stays constant (remember, this distribution is the hop’s fingerprint).
This means that knowing the aroma and flavor of a given variety is sufficient. If you become familiar with a particular variety’s aroma and flavor, percent alpha, the name of the variety, and, perhaps, the total oil content is all the information you need from the supplier.
Before buying hops, study their color and aroma. Hop pellets should have an olive-green color. Hop cones (whole hops) should be a little brighter green. If the color is pale yellow to ivory, don’t take the gamble. These paler colors suggest that the hops are too well aged.
Buy only hops stored in a refrigerator. Hop deterioration is directly related to temperature. Cold hops last longer than warm hops. At Coors they store their hops at 28˚ F and keep a three-year supply on hand (at least that’s what the tour guide said). The point is that cold storage greatly extends the hops’ shelf life.
Hops should not be exposed to air, since oxygen breaks down alpha acids and causes beta acids to smell like parmesan. Hops are compressed into hop plugs, hop bales, or pellets to minimize oxygen damage. However, these preparations still require packaging. Some of the best packages on the market are vacuum-packed or nitrogen-packed bags that do not allow oxygen to enter. Plastic storage bags, for example, do allow oxygen to enter the package.
Experimentation
The best way to get to know different hops is to experiment. You can brew five gallons of wort and split it into several small kettles to play with different varieties, concentrations, or times of addition. Likewise, you can brew a five-gallon batch and split it into several vessels for dry hop trials.
Just remember that every good experiment needs a control or “no treatment” group. If you don’t include a control, you’ll never know if a change actually added that funky flavor or if the funky flavor was from another ingredient.
Using hops to improve your brew isn’t difficult. Buy healthy looking and smelling hops, experiment, take notes, use different varieties, and enjoy the many tastes and smells hops provide.
