Hops are the flowers of the hop plant. They have glands in the flower (the hop cone) that contain a powder called Lupulin. This powder contains substances that are bitter (the Alpha and Beta acids). The glands also contain oils (called essential oils) that have a pleasant aroma.

The use of hops was discovered in the Middle Ages in Europe. For many years, “brewers” had added traditional plants to Ale to change or improve the flavor. Ale was a simple, bland drink fermented from malt. They found that hops, when added to Ale, gave a distinct and pleasant flavor. More importantly, they realized that hops also helped to preserve the beer. This is because hops contain compounds that slow down or stop bacterial growth. This is known as bacteriostatic.

Hops today are used mainly for their flavor and aroma. Most breweries today pasteurize their beer so that the bacteriostatic properties of hops are not important. However, in some countries dry hops are still added to beer. Dry hopping means adding dry whole hops to a cask or a tank. Dry hopping adds aroma and helps preserve the beer where it is sold in casks.

Hops  are  typically  sold  to  brewers  either fresh (wet), as dried whole hop leaf cones, or as hop pellets. 

Fresh (Wet) Hops – are sold directly from the field to the breweries.  They are valued for the “fresh hop  characteristics”  they  can  add  to  a  beer.    Fresh  hop  shelf  life  is  measured  in  hours  and  they  have to be utilized by brewer as soon as possible after being harvested.

Dry  Hops  –  are  hops,  which  have  been  dried  and  stored  until  they  can  be  sold  either  as  dried  whole hop cones or are further processed into hop pellets. Drying, pelletizing, packaging and cold storage allow hops to be sold to brewers year round. The majority of hops used by brewers are in a dried/pelleted format.

Pelleted  Hops  –  There  are  two  types  of  hop  pellets,  the  T-­‐90  pellets  which  are  prepared  from  whole cone hops. The T-­‐45 hop pellets are similar to the T-­‐90 pellets; however, they are milled at a  lower  temperature  to  remove  the  stickiness  of  the  lupulin  and  some  of  the  vegetative  matter. Brewers like the pelleted hops for the consistency of quality and supply they can offer.

Hop Biology

Hops are one of the two members of the plant family Cannabinaceae, which includes hemp and cannabis, and which is closely related to the nettle and hemp families. Wishful thinkers please note that Cannabis and hops cannot interbreed. There are only two recognized species of hops: humulus lupulus and humulus japonicus. Humulus japonicus is an annual with virtually no resins, and is useless for brewing, although it is a very attractive vine.

Hops are found in temperate (cooler) zones of the world between latitudes 350 and 70(see diagram below). The latitude is important as a long day with a length of 15 hours or more is needed for flowering. Their natural distribution range is in the Northern Hemisphere where they can be found growing wild in hedgerows. They are now cultivated all over the world. They are even being cultivated at the very edge of the normal growing range. In South Africa they use lights to extend the day length.

The plant regrows annually from the same rootstock. It produces long bines between 4 and 7 meters high (depending on variety and growing systems). These are usually supported on overhead wires in the hop gardens or hop yards. Bines grow rapidly in the spring. As days get shorter the bines stop growing vertically. They then produce side arms that bear the flowers.

In addition to water, cellulose, and various proteins, the chemical composition of hops consists of compounds important for imparting character to beer.

Alpha acids
Probably the most important chemical compound within hops are the alpha acids or humulones. During wort boiling, the humulones are thermally isomerized into iso-alpha acids or isohumulones, which are responsible for the bitter taste of beer.

Beta acids
Hops contain beta acids or lupulones. These are desirable for their aroma contributions to beer.

Essential oils
The main components of hops essential oils are terpene hydrocarbons consisting of myrcene, humulene and caryophyllene. Myrcene is responsible for the pungent smell of fresh hops. Humulene and its oxidative reaction products may give beer its prominent hop aroma. Together, myrcene, humulene, and caryophyllene represent 80 to 90% of the total hops essential oil.

Xannthohumol is the principal flavonoid in hops. The other well-studied prenylflavonoids are 8-Prenylnaringenin and isoxanthohumol. Xanthohumol is under basic research for its potential properties, while 8-prenylnaringenin is a potent phytoestrogen.

For brewing, the useful part of the plant is the female flower or cone, also called a strobile. It is easily distinguished from the five-petaled male flower, as the cone is much larger and is made up of many scale-like bracts. The cone is made up of a central stem, called a strig. Bracts, which contain no resin-producing glands, and bracteoles, which do, are little petals attached to this central stem. At the base of each bracteole is the seed (if any) and the lupulin glands – the most important part of the plant to a brewer. The lupulin glands are tiny and yellow, filled with the resin containing alpha and beta acids and hop oils. Because the lupulin glands look somewhat like pollen, they are easily mistaken for it, but they are not at all the same.

The lupulin resin is made up of a number of different acids and oils, each of which contributes in a slightly different way to the brewing process. Those of primary interest to the brewer are the alpha and beta acids. There are three main alpha acids: humulone, adhumulone, and cohumulone. Adhumulone occurs in only minor amounts, and is not known to be particularly important. Humulone is the most studied alpha acid, with cohumulone being the subject of much controversy among brewers and researchers. Cohumulone is thought to produce a harsher bitterness, so that a low cohumulone profile is often sought. Nevertheless, some of the new high-alpha hops contain high levels of cohumulone, and are still popular. Alpha acids produce bitterness in beer, critical to the dry-sweet balance which gives beer character. They are, however, not water-soluble, and must be boiled in the wort in order to isomerize.

Brief History of Hops

Hops have a long history, from the Babylonians who used them to brew some of mankind’s first beers, to the Romans who brought hops to Britain to use as a vegetable.

The Latin name for the hop is Humulus lupulus or “wolf of the woods”. The wild plant, from which the modern hop has been developed, is as old as history itself. The plant first attracted attention, not as an ingredient in beer but as a medicinal herb in ancient Egypt.

The first reference to hops in continental Europe appeared in 736 AD, and records of cultivated hop gardens, associated with monasteries in France and Germany in the 8th and 9th Century, growing hops for their medicinal properties. The first mention of hops being added to beer appeared in 1079.

It took six more centuries, however, before hops were widely accepted in the brewing of beer, eventually replacing gruit. Gruit, a combination of herbs, often including rosemary and yarrow among others, was used for brewing beer, and each brewer had his own secret combination. Those brewers were understandably quite antagonistic about the hop. Nevertheless, hops gradually made inroads.

In the 1300’s, the Dutch began importing hopped beer and then began brewing their own. Hops were planted in England by the early 1400’s and in 1436, Henry VI praised hopped beer as “notable, healthy, and temperate.”

In Bavaria, the Purity Law of 1516 outlawed traditional bittering compounds and decreed that only hops could be used to bitter beers.

At first the American colonists imported English hops, but in 1629, the e Massachusetts Bay Colony ordered seeds to be shipped from England, and by 1640 colonists were harvesting their own hops.

Abbot Adalhard

The first documented link between hops and brewing comes from Picardy in Northern France, in 822, where Abbot Adalhard of the Benedictine monastery of Corbie, in the Somme valley near Amiens, wrote a series of statutes on how the abbey should be run. The many rules covered areas such as the duties of the abbey’s tenants, which included gathering of firewood and also of hops. Adalhard also said that a tithe (tenth) of all the malt that came in should be given to the porter of the monastery, and the same with the hops. If this did not supply enough hops, the porter should take steps to get more from elsewhere to make sufficient beer for himself:

Hildegard of Bingen

Hildegard of Bingen c. 1098 – 1179, (Saint Hildegard and the Sibyl of the Rhine) was a German Benedictine abbess and polymath active as a writer, composer, philosopher, mystic, visionary, and as a medical writer and practitioner during the High Middle Ages.She is one of the best-known composers of sacred monophony, as well as the most recorded in modern history. She has been considered by many in Europe to be the founder of scientific natural history in Germany. Hildegard wrote theological, botanical, and medicinal works that contains one of the earliest reference to hops.


When exactly hops began to be cultivated for putting into beer, rather than just being gathered wild from forests, is surprisingly unclear. German sources today claim that hop gardens appear in records dating from the second half of the ninth century in and around Hallertau, in Bavaria, Southern Germany, which is still the world’s largest single hop-growing area. The best evidence seems to be that commercial hop cultivation happened in Northern Germany first, and not until the 1100s or 1200s, feeding the breweries of the Hansa trading towns, which were exporting hopped beer from at least the 13th century onwards.

Hop Varietal Specifications

There are hundreds of varieties of hops in use throughout the world. Some are differentiated by their agronomic characteristics, some by their use in brewing. Many older varieties have fallen out of favor due to changes in the brewing industry; in the past, brewing was done only when the hops were ready, so storagability was less important. Likewise, many older varieties performed well only in specific areas, and have not adapted well to modern large-scale, widespread hops production. Over the years, hops have been developed to grow both short and tall, for disease and pest resistance, and for higher alpha-acid production.

Hops are usually divided into ‘bittering’, ‘aroma’, and ‘noble’ varieties. Bittering hops usually have a higher alpha-acid content than the others, and store very well. They may not have a particularly pleasant aroma, however, and are not usually used for both purposes. In contrast, aroma hops have a lower alpha-acid content, but a higher hop oil content. They don’t age as well as bittering hops, but can be used as both bittering and aroma hops in the same beer. Noble hops are a special group.


Noble hops are a special group. There are four recognized varieties: Hallertauer Mittlefrüh, Tettnang Tettnanger, Czech Saaz and Spalt Spalter. They are primarily aroma hops, but many of the classic European lagers use them for both aroma and bittering. True noble hops can only be grown in the correct region. Noble hops are characterized by an alpha:beta ratio of about 1:1, relatively low counts on both acids, and a high humulene level. Cohumulone and myrcene levels are low, and the hops do not tend to store well. There are a number of varieties which perform almost the same way in brewing, and which, while not ‘true’ noble hops, are excellent substitutes for the North American grower.


Bittering hops vary wildly in alpha acid content. Contemporary varieties like Pacific Gem, which was developed in New Zealand specifically for organic cultivation and high bitterness, have about 18.5% alpha acid, compared with older bittering varieties like Nugget at 12-14% or Centennial at 9-11%. These new high-alpha hops tend to store well, and brewers use much smaller quantities of them in each batch, making them economical for the brewer. It is also easier for the new grower to achieve good results with these high-alpha hops, making them an excellent choice for novices.


Aroma hops are a little trickier, as their lower alpha levels and high oil content are more dependent on soil, weather and water. However, brewers tend to be less concerned with alpha ratings on these hops, as they are not being used to bitter the beer. In fact, variable results from year to year can be turned to the grower’s advantage, as both brewer and grower can capitalize on the uniqueness of each year’s production. This is a major advantage for the small grower working directly with small breweries, where uniqueness is valued. Large national or international breweries value consistency above all else, and are inappropriate markets for smaller producers of more diverse hops.


This group represents the continuum of Germanic hops, from the dry herbaceous, almost minty aromas of the classic Hallertau Mittelfrüh and its related varieties, through spicy varieties like Hersbrucker and Spalt and their variations to more modern, and even somewhat bent versions of the basic idea. They all tend to be low- to mid-alpha content, bred specifically for aroma.

This is a family of hops with Saaz as its spiritual homeland. The Saaz family is generally described with that vague word “spicy,” but once you smell them, you know that word isn’t relatives thrive in far-flung places like Poland, the United States, and Asia. As you move to the bottom of the list, the aromas get less pure and Saazy, picking up notes of fruit, lemongrass, and other complex aromas.

Classic English hop aromas are difficult to describe, but are often characterized as green, tangy, and a bit grassy, perhaps with some spiciness as well. This uniquely English character is crucial for pale ales and IPAs. East Kent emerged as the English hop-growing region during the eighteenth century, and Goldings from that area were the hop of choice for the strong, pale, and very highly hopped October beers that would eventually morph into IPAs a century later. 

Styria is a region in Slovenia where a form of Fuggles has been grown for a century or more under the name Styrian Goldings. In that location, Fuggles are more ethereal and less earthy than in their homeland, and are elegant enough to stand alone in pale beers, and are especially popular in Belgium for that purpose. On this list, the classic variety is in the middle; above it, the hops get even more bright and elegant; below it, a bit earthier and spicy. All the hops in this category have very nice aromatic characteristics.

In the 1970s classic Old World varieties crossed with New World wild hops and created new strains with pungent, floral, piney, and citrusy characters. These became the heart and soul of the new American pale ales that emerged around 1980 with beers like Anchor Liberty Ale and Sierra Nevada Pale Ale.

This is a slightly unruly group of newer hops with fairly distinct personalities, showing aromas of apricot, passion-fruit, wine grapes, and other fruits.

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