CHAPTER 4

Hops

Hops are the conelike female “flowers,” strobiles, of the vining Humulus lupulus. The strobiles are formed by a cluster of petallike, yellowish-green bracts and bracteoles emerging from a central stem. Each bract bears many tiny glandular sacs (trichomes) of lupulin at its base. Lupulin accounts for as much as 15 percent of the weight of the hop. The yellow lupulin is composed of essential oils, resins/bittering principles, polyphenols, nitrogen, sugars, pectin, lipids, and wax.

The resins may be classed alpha acids, beta acids, and gamma resins. The alpha and beta acids are “soft,” whereas the gamma resin is hard, and contributes nothing to the brewing.

The alpha resin group is the most important hop fraction, and the most stable. Alpha acids have no aroma but are intensely bitter. They are responsible for the hops’ bacteriostatic contribution to the brew. Alpha acids (humulone, cohumulone, and adhumulone) may be are isomerized during boiling (their atoms are rearranged) to somewhat soluble and even more bitter iso-alpha acids.

In contrast, the beta acids (lupulone, colupulone, and adlupulone) are far less stable than alpha acids, are extremely subject to oxidation, and are only slightly soluble. They become even less soluble as the hot wort cools, and are deposited in the trub as an amorphous yellow precipitate. Very little of their antibiotic, aromatic, and bittering properties are carried into finished beer unless they are oxidized, in which case they are extremely bitter, but the hops may taint the beer with an unpleasant spoiled-vegetable taste.

Varieties of hops that are high in alpha acids are generally preferred for bittering beer, because less hops are thereby required to achieve target bitterness levels. Because the amount of alpha acid that is isomerized by boiling is in large part time-dependent, hops for bittering are generally boiled in wort for thirty to ninety minutes. Boiling, however, drives off hop flavor and aromatics. Where hop flavor is desired, some isomerization efficiency is given up, and “flavor” hops are only boiled for five to thirty minutes.

Hop aromatics are even more fugitive; although some aromatics survive boiling for as long as twenty to thirty minutes, the full, fresh aroma of hops is only captured by “dry-hopping,” or adding whole hops or their extract to the conditioning beer after fermentation. Hop-oil esters and floral ketones are generally evaporated more quickly than the terpene and sequiterpene oxides and alcohols that give beer a spicy flavor/aroma and greater mouthfeel.

The other major contribution of hops to the finished beer is the tannins they dissolve into the boiling wort. Tannins are complex, generally oxidized polyphenol polymers. When proteins and proteoses come into contact with the astringent-tasting amorphous flakes, they adhere to them and, by virtue of their increased mass, are precipitated out of solution. Because there are generally fewer hop tannins than proteins, they do not usually carry over into the finished beer and significantly affect flavor.

Although the bitter flavor and tangy aroma of the hop is now considered an essential complement to the malt sweetness of beer, hops were first employed in brewing as a preservative. Beer made with hops stored better than beer brewed without them, although the reason why was not understood. Only toward the end of the nineteenth century did brewers discover that hops prevented the growth of many waterborne and airborne bacteria. The role that hop polyphenols play in precipitating unstable proteins in the kettle, thereby reducing the potential for chill haze in the beer, also began to be understood.

On the Vine

Hops are grown on perennial vines that trail along wires strung on trellises fifteen to twenty-five feet above ground level. Each year new stems twine clockwise around the wire strands supporting the strobiles. When the strobiles are mature, the plant is cut loose from the trellis, and the clusters of hop cones are stripped from the stems of the plant.

Hops that are of brewing quality must be harvested during the five to ten days of their prime. Immature hops are very green and have a haylike aroma; overripe cones have rusty-colored petals, tend to shatter easily, and have a harsh smell.

The cones, which contain 70 to 80 percent moisture at harvesting, are dried to 8 to 10 percent moisture (usually at 140 to 150 degrees F [60 to 65 degrees C] but sometimes below 130 degrees F [55 degrees C] when a very strong aroma is characteristic) over a period of eight to twelve hours. They are sometimes fumed with sulfur to lighten their color and give them a softer, silkier, more appealing feel. Dried hops are cured in cooling bins for five to ten days to equalize their moisture content, improve their aroma and appearance, and make the cones more resilient against shattering. They are compressed and baled, each bale measuring approximately twenty by thirty by fifty-four inches and weighing between 185 and 205 pounds. They are traditionally stitched in burlap hopsack, but modern foil-mylar laminate vacuum-packaging under nitrogen or CO₂ atmosphere is gradually replacing burlap.

Hops on the Vine

The harvest is purchased by hop merchants, who hold the hops in cold storage until they are sold to the brewer. If the hops have been properly dried and baled, protected from direct sunlight, and stored at low humidity and low temperatures (33 degrees F [1 degree C] is ideal), little destructive oxidation occurs; hops that have a beta-acid content equal to their alpha acids store better than hops with a low percentage of beta acids. Under ideal conditions hops will keep for up to two years. Under adverse storage conditions, however, the essential oils are driven off, and many of the alpha-acid resins are oxidized to uncharacterized bitter substances or to useless hard resins. Such hops may have an “off” cheesy, soapy, or other disagreeable aroma and may be yellow or brown. At this point, their bittering strength has been greatly diminished and their flavor contribution to beer is abnormal.

In the Brewery

Brewing hops should be whole cones of a light yellowish-green color, not mottled or spotted, roundish or slightly elongated in shape, and of less than 6 percent stem and leaf content. They should have a pleasant aroma; it is this bouquet that indicates the condition of the essential oils. The hop cones should be silky, glossy, and springy to the touch. Small hops tend to be of finer quality than large hops.

Two or three small cones should be rubbed in the palm of the hand and sniffed to assess the aroma. The lupulin quality and content can be judged by the stickiness left on the hand. Several cones should be broken lengthwise and the quantity and color of the lupulin assessed. It should be lemon colored and plentiful. Old, deteriorated hops have powdery, light-brown lupulin and range in color from green or greenish-yellow to yellow or brownish-green. Usually the discoloration is obvious. Old, dry, and powdery hop cones should be avoided, as the alpha-acid content will be considerably reduced. The deterioration of old or mishandled bales may account for a 50 percent or greater loss of alpha acids. This is also true in the case of lots containing an excessive number of broken cones. Improved oxygen-barrier packaging is becoming an important factor to brewers, since it can cut alpha-acid losses to a fraction of what can be expected with burlap-baled hops.

An alpha-acid analysis is usually made of samples taken from each hop bale. Alpha acidity is given as a percentage of the sample, by weight. This is stated by the dealer and is used by the brewer to adjust bittering-hop rates.

Alpha acids go into solution only after boiling has isomerized them to iso-alpha acids. Their bittering contribution is dependent upon isomerization efficiency in the kettle and the quantity and alpha-acid content of the hops used. Several methods for the quantitative analysis of iso-alpha acids make it possible to estimate the hop bitterness in beer; the internationally agreed upon standard is bitterness units (IBU). One IBU equals .0001335 of an ounce (avoirdupois) of iso-alpha acid per gallon of solution, or one milligram per liter.

Where stated in a beer profile, bitterness units are used to target bittering-hop rates, adjusting the amount to reflect the widely varying alpha-acid content of hops from lot to lot and season to season.

Dave Line (The Big Book of Brewing) devised the alpha acid unit (AAU) to simplify these adjustments; his method was adopted by the American Homebrewers Association as the homebrew bitterness unit, or HBU. One AAU/HBU equals one ounce of a l percent alpha-acid hop. Using this system, two ounces of a 5 percent alpa-acid hop gives 10 HBU, and so on.

Assuming 30 percent isomerization/utilization of the alpha resins by a 90- to 120-minute rolling boil, each HBU will contribute 22.472 IBUs to a gallon of wort, or 85 IBUs per liter. Where utilization is high, dividing the IBU given for any beer by 22.472 can approximate the HBUs required per gallon of wort. Likewise, where bitterness units aren’t given in a recipe, they can be roughly figured by multiplying the AAUs given by 22.472 (per gallon of wort). More accurate predictions of bitterness can be made using table 18. In any case, bitterness units can only be accurately matched if fresh, properly stored hops are used; with oxidized hops, alpha acidity is diminished and the proper hop rate becomes guesswork.

Hop Cross-section

Table 9: Hops

Color Range
Low-quality hops	High-quality hops	Deteriorated hops
Dark green	Yellowish-green	Yellow
Olive green	Greenish-yellow	Brownish-yellow
Mottled brown-green		Brown
		Brownish-green

Cone Size
Large	Medium	Small
2 ¼–3" long	1 ¼–2" long	¾–1" long

Analysis
MC	8–13%
Resins	7–20%
Alpha acid	4–15%
Cohumulone %	20–40%
Alpha:beta ratio	.8–3.5
Essential oils	.2–3%
Tannins	2–5%
Nitrogen	2–4%
Fats and waxes	2–5%
Hop storage index	50–85%

Varietal and lot analyses of hops include several commonly quoted parameters; only the percentage of alpha acid, the alpha:beta ratio, the percentage of cohumulone, and the percentage of total oils seem to be of definite significance. Other indicators are much more subjective; the hop storage index (percent alpha acid after six months storage at 68 degrees F [20 degrees C]), for instance, is a guideline only, since merchants and brewers store hops under varying temperature and packaging conditions. Percentages of the significant hydrocarbon fractions, taken into consideration with the percentage of total oils, may to some extent indicate the aroma that a hop will give, but the compounds actually responsible for the flavors and aromatics that brewers prize have not been defined. Furthermore, although it is known that oxygenated hydrocarbons, especially terpenes and sesquiterpenes, are less volatile and contribute a major part of hop flavor and aroma to wort and beer, synergic relationships between them and their esters, alcohols, and acids are not understood. Consequently, aroma and flavor characteristics cannot be defined from laboratory data.

The ratio of alpha to beta acid and the percentage of cohumulone do seem to have some significance regarding the fineness of wort bitterness, but there are exceptions to the brewer’s rule that the best hops have a high beta-acid ratio and a low percentage of cohumulone.

Hop bitterness is accentuated by magnesium, carbonate, and chloride ions, and hop rates must generally be reduced as these increase; historically, brewers have employed carbonate and chloride waters only for malty, low-hopped beers. Increasing amounts of sulfate, on the other hand, give a cleaner hop flavor. Well-hopped beers brewed with gypsiferous liquor commonly exhibit a finer, less coarse bitterness than is obtained with other liquor profiles.

Hop pellets have gained in popularity with brewers in recent years because they are less susceptible to oxidation during storage, especially under adverse conditions. Pellets stored under the same conditions as whole hops will lose only about one-third the alpha acids that whole hops will lose. They are compressed from fresh hops and foil-packaged in an oxygen-free environment. Because pellets are almost invariably less deteriorated than whole hops, utilization is usually 3 to 10 percent better (5 to 35 percent; as opposed to 3 to 30 percent for whole hops).

Table 10

Part A: Hop Varieties
Hop Varieties	% Alpha Acid	% Beta Acid	Cohumulone, % of AA	Total Oils mL/100g	M	H	C	F	%AA after 6 mo. @ 20°C	Origin
					% of each:
Czech Saaz	2.5–4.5	2.5–4.0	22–28	.4–.7	23	43	11	13	50
Polish Lublin	3.0–4.5	2.5–3.5	25–30	.7–1.2	30	38	10	11	50
Spalt	4.0–5.5	4.0–5.5	23–28	.5–1.1	20	22	13	13	55
U.S. Spalt	3.0–6.0	3.0–5.0	20–25	.5–1.0	45	15	5	13	50
Tettnang	3.5–5.5	3.5–5.0	23–29	.6–1.1	23	23	8	14	60
U.S. Tettnang	3.0–5.0	2.5–4.5	20–25	.4–.8	41	21	7	7	60
H Hersbruck	2.0–5.5	3.0–5.5	19–25	.7–1.3	20	20	10	<1	60
U.S. Hersbruck	3.5–5.5	5.5–7.0	20–30	.6–1.2	45	25	8	<1	50
H Hallertau	2.5–5.5	2.5–5.5	18–24	.6–1.2	20	33	12	<1	55
U.S. Hallertau	3.0–5.5	3.0–5.5	18–24	.6–1.0	40	34	11	<1	55
U.S. Perle	5.5–9.5	3.5–5.0	27–32	.7–.9	50	31	11	<1	85	NBrwr+
Mt Hood	3.0–6.5	3.0–5.5	24–30	.6–1.2	38	38	11	<1	50	Hal+
Liberty	3.0–5.5	3.0–4.5	24–30	.6–1.2	38	38	11	<1	45	Mtlfh+
Crystal	2.0–4.5	4.5–6.5	20–26	1.0–1.5	52	21	6	<1	50	Hal+
Cascade	4.5–8.0	4.0–8.0	30–40	.8–1.5	53	13	4	6	50	Fug+
Bav N Brewer	6.0–10.	3.0–5.0	28–33	1.6–2.1	33	28	9	<1	75	BGold+
U.S. N Brewer	6.5–10.	1.5–5.0	20–30	1.5–2.0	55	25	8	<1	80
Nugget	12.0–16.	4.0–8.0	24–30	1.7–2.3	55	18	9	<1	75	BGold+
Eroica	9.5–14.	2.5–5.0	36–42	.8–1.3	60	1	10	<1	60	BGold+
Centennial	8.5–12.	2.5–5.0	29–30	1.5–2.3	50	14	7	<1	65	BGold+
Galena	12.0–15.	7.0–9.5	38–42	.9–1.2	58	13	4	<1	65	BGold+
Brewers Gold	7.0–10.	3.0–4.5	40–45	1.8–2.5	63	15	8	<1	55
Chinook	10.0–14	2.5–4.0	29–34	1.5–2.5	38	23	10	<1	70	Fugl+
Styrian Gldng	4.0–6.0	2.0–3.0	26–30	.5–1.3	30	36	10	3	65	Fugl+
Willamette	4.0–7.0	3.0–4.5	26–35	1.0–1.5	50	25	8	6	65	Fugl+
U.S. Fuggle	4.0–6.0	1.5–3.0	25–32	.7–1.2	45	23	8	5	65
UK Fuggle	4.0–5.5	2.0–3.0	25–30	.7–1.1	26	37	12	9	60
BC Goldings	4.0–6.5	1.5–2.5	22–28	.8–1.1	26	41	13	<1	60
UK Goldings	4.5–6.5	2.5–3.5	22–32	.8–1.0	24	45	14	<1	55	Kent+
Pride Rngwd	6.0–10.	3.0–6.0	33–39	1.0–2.0	38	6	8	<1	55
Cluster	5.5–10.	4.5–8.0	36–42	.4–.8	50	17	7	<1	85	BGold+
UK Challenger	6.5–8.5	3.0–4.5	22–28	1.0–1.5	31	29	9	2	55	Chal+
UK Northdown	7.0–9.0	4.5–7.0	28–32	1.2–2.2	25	43	15	<1	60
Chart compiled from references provided by Morris Hanbury and HopUnion.
Notes: % alpha acid and % total oils vary widely year to year.
M=Myrcene, H=Humulene, C=Caryophyllene, F=Farnesene. These are significant hop oil hydrocarbons; their respective amounts help define aroma characteristics.

Part B: Hop Producing Districts
Country of Origin	Hop Type	Grown
Czech Republic	Saaz/Zatec Red	Zatec, Auscha, Raudnitz, Dauba
Germany	Hallertauer/Mittlefrueh	Hallertau, Baden
	Tettnanger	Wurtenburg
	Spalt	Spalt
	Hersbrucker/Gebirg	Hersbruck
Yugoslavia	Savinja/Styrian	Wojwodina, Slovenia
	Goldings
Belgium	Hallertau/Saaz	Alost, Poperinghe
United States	Various	Yakima Valley (Washington)
		Willamette Valley (Oregon)
		Boise and Snake River
		Valleys (Idaho)
Australia	Pride of Ringwood	Victoria, Tasmania

The most highly prized hops in the world are the mild southern-English and central-European varieties. Although these and similar types are being more widely cultivated in the western United States, they are not frequently used by large domestic commercial breweries. New disease-resistant, high-alpha-acid varieties are emerging that also have desirable aromatic qualities, giving better kettle utilization and economy without forsaking fine hop character, as has been the case with high-alpha-acid-percentage strains previously developed for economical use.