Hop Cultivation

The plant family known as Cannabaceae is home to two well-known members that have garnered significant attention and admiration around the globe. These members belong to the genera Cannabis and Humulus. Within the genus Cannabis, the species Cannabis sativa stands out prominently, and it is commonly recognized by the names marijuana or hemp. Throughout various epochs in human civilization, this species has been utilized for multiple applications. These include the crafting of fabrics such as cloth and rope by using its fibrous attributes, as well as the employment of the plant for therapeutic purposes within traditional medicine. In more recent historical periods, Cannabis sativa has acquired notoriety as a substance used recreationally. This reputation has often overshadowed its medicinal potential. However, a resurgence in acknowledging its therapeutic properties is occurring in contemporary society, and the plant is now being more widely accepted and appreciated for its medicinal benefits.

In a parallel vein, the sister genus of Cannabis, Humulus, proudly features its renowned species, Humulus lupulus, which is more commonly referred to as the common hop. This plant has fascinated many due to its striking resemblance to marijuana in terms of visual appearance, aroma, and even medicinal properties. As legal restrictions surrounding marijuana have started to lift within various states, a collaborative environment has emerged between marijuana growers and scientists focused on hop genetics. This synergy has led to the discovery of significant botanical commonalities between the two plants. These similarities extend beyond mere appearance, encompassing a broader spectrum of characteristics that include the cultivation and breeding of the plants for specific aromatic qualities. By acknowledging and exploring these shared traits, both growers and scientists can draw upon each other’s expertise, fostering an environment of learning and innovation.

Reproduction and Cultivation

The hop plant, a perennial climber known for its dynamic growth, undergoes an intriguing cycle of dieback and regeneration. During winter, the hop dies back only to revive in the spring, commencing a growth cycle that repeats year after year in temperate climates. Under optimal conditions, the growth of hops can be astonishingly rapid, stretching as much as 1 foot (30.5 centimeters) in a single day. Over the course of a season, with an adequate support system, a hop plant can reach towering heights of 40 feet (12.2 meters). While the above-ground bine of the hop regenerates annually, its below-ground system of roots and rhizomes remains a constant, permanent fixture. The roots of the hop can penetrate the soil to a depth of 15 feet (4.6 meters) or more, extracting essential nutrients, minerals, and water to nourish the plant.

The rhizomes, a distinctive part of the hop’s underground system, are unlike roots. They are actually stems that grow horizontally just beneath the soil’s surface and can extend up to 5 feet (1.5 meters) in length. These robust roots and rhizomes are well-adapted to overwinter below ground. In fact, the cold winter season is indispensable to the hop, as it requires a dormant period of at least six to eight weeks to yield the valuable flowers that are vital in beer brewing. Come spring, the hop reawakens, and the buds on the rhizomes sprout into shoots. This entire underground structure, encompassing roots and rhizomes, is referred to as the plant’s crown, which in a mature hop plant can spread as wide as 4 feet (1.2 meters) across.

Another fascinating aspect of hop plants is their dioecious nature, meaning that the plants are distinctly male or female. This contrasts with many other plants that are monoecious, essentially unisex, with both male and female reproductive parts on the same plant. While a monoecious plant can self-fertilize, creating seeds and reproducing itself, a dioecious plant like the hop requires proximity between male and female plants for pollination and viable seed production.

Interestingly, modern hop growers usually avoid cultivating male hop plants, preferring to propagate new hop plants from existing rhizomes. Several reasons contribute to this choice. First, the flowers produced by male plants, unlike the cone-shaped flowers of female plants, lack the necessary characteristics for quality beer production. Second, growers prefer to prevent the female hop plants from being pollinated and producing seeds, as seeds add unwanted weight to the hop flowers. Since brewers purchase hop flowers by weight, they do not wish to pay for seeds that add no value to the brewing process.

Hops exhibit a trait known as heterozygous, meaning that a seed produced by a particular hop variety is unlikely to mature into a plant that maintains the same variety as its parent. This genetic unpredictability made propagation from seeds unreliable for achieving desired hop varieties. Therefore, the reliance on hops propagated from rhizomes became the preferred method, as it ensured that the specific variety being sought was indeed what was being cultivated.

Today, male hop plants are generally maintained only by growers who are engaged in the development of new hop varieties. These male plants are kept in isolation from commercial hop yards to prevent any unintentional cross-pollination. For those who cultivate hops and find wild hop plants growing nearby, vigilance for male plants is advisable. Removing them helps prevent unintentional cross-pollination with cultivated female hops. However, instead of destroying these wild male plants, a considerate approach might be to preserve the unique genetics of the wild plant by propagating a rhizome or cutting and relocating it a safe distance from the hop yard. By doing so, you can avoid cross-pollination while conserving the wild plant’s genetic heritage.

Hops' Growth Cycle

Fresh hops cones growing
Hops growing in the field

Hops are known for their impressive growth, achieving great size at a rapid pace. This extraordinary growth is fueled by an insatiable need for sunlight, a rich supply of nutrients from the soil, and an abundance of water.

Spring Emergence and Pruning:
As the early spring sun begins to warm the earth, the rhizomes within the hop plant’s crown initiate a burst of shoots. It falls upon the diligent hop grower to carefully prune these shoots, selecting only a handful of the strongest to train up their chosen support system. Pruning is more than a mere aesthetic choice; it’s a critical step in directing the plant’s vigorous energy towards the production of its prized flowers rather than a chaotic tangle of bines.

The Climb of the Bines:
Unlike vines, which employ thin, spiraling shoots to wrap around anything they can reach, hop bines use tiny barbs known as trichomes to ascend. These microscopic, anvil-shaped barbs enable the bine to twist itself around and upward, grasping anything in its path, even including other shoots from the same plant. If examined under a microscope, each trichome’s sharp ends become evident, making hop bines a prickly customer indeed.

The Flowering Stage: 
Once the hop reaches the zenith of its support system, its focus shifts to producing horizontal shoots known as sidearms. Established plants, generally in their second or third growing season, reach this stage between late June and early July. By midsummer, these side shoots begin to form buds that will blossom into the distinctive hop flowers. Initially appearing as tiny, bright green beads of vegetation called burrs, they mature into the papery, pinecone-like shapes known as cones.

The Composition of Cones:
Within these unique cones, the outer scales (or green petals) are termed bracts, while the more delicate interior scales are called bracteoles. At the base of these bracteoles, glands produce a bitter yet aromatic yellow resin that resembles pollen at first glance. This resin, known as lupulin, consists of essential oils and alpha and beta acids that contribute to beer’s characteristic bitterness. Alpha acids add the bitter flavoring and also function as a preservative, while beta acids add a touch more bitterness and aroma. Each hop variety boasts its own distinct balance of these acids, and their levels can vary annually due to changing growing conditions. Ultimately, the precise composition of alpha and beta acids and essential oils will dictate the particular type of beer for which the hops will be most suitable.

Harvesting & Processing

Rear view of Hop Harvester harvesting hops
Rear view of Hop Harvester harvesting hops
Hop harvesting
Hops being harvested
Hops being sorted
Hops being sorted
Hops drying in automatic kiln
Hops drying in automatic kiln
Hop Kiln
hops farmers working with hop picking machine , Villoria village , Leon, Spain
Hops being sorted

During the hop harvest, a symphony of carefully coordinated actions begins to play out, all attuned to the delicate growth and energy cycle of the Humulus lupulus plant. It’s a period of intense activity where precision and timing converge, transforming the raw green bines into the essential ingredients that brewers across the globe treasure.

When the harvest season descends, a process more nuanced than merely severing the bines from their support system is set into motion. Rather than cutting them at ground level, a section of the bine, approximately three feet in length, is intentionally left uncut, a sentinel protruding from the earth. This deliberate act serves multiple purposes. By leaving this part of the bine intact, it not only aids in preserving the plant’s energy for the next growth cycle but also facilitates handling during the harvesting process.

Once cut, the bines are meticulously transported to a central location where the true harvest commences. This strategic relocation is not merely a matter of convenience; it’s a well-thought-out maneuver to ease the process of collecting the valuable hop cones. In large-scale operations, specialized machines await the bines, ready to separate the cones from the leaves and stems efficiently. In smaller, more artisanal settings, skilled hands might undertake this task, each cone plucked with a knowledge and reverence passed down through generations.

The harvested hops are then subjected to the crucial drying process. Spread out in oasthouses or hop kilns, the moisture content is reduced, preserving the flavor, and preventing spoilage. It’s a delicate dance of temperature and timing, where the essence of the hop is captured and retained.

After drying, the hops may be further processed into pellets or baled, depending on the brewer’s preference and the intended use. Packaging and storage then follow, each step a testament to the craft and science that underpin this age-old practice.

Interestingly, the remaining bine’s biological functions don’t cease with the harvest. Through the complex process of photosynthesis, it continues to produce energy, transforming sunlight into carbohydrates. This energy is then channeled and stored within the expansive root system of the hop plant.

With the onset of cold winds and the formation of hard frost, the above-ground portion of the hop plant yields to the winter’s freezing temperatures and dies, marking the conclusion of its growing season. This does not represent the total cessation of life but merely a transition, as the resilient part of the hop plant, known as the hop crown, remains secure beneath the earth’s surface. There it enters a period of dormancy during the winter months.

Dormancy in this context should not be misconstrued as a failure or cessation of life, but rather a tactical withdrawal. This phase allows the hop plant to endure the severe conditions of winter. The energy that has been accumulated and stored within the roots acts as a guarantee for the plant’s vigorous resurgence when spring reappears. This cycle readies the plant for another growth season, where it will once again thrive, be harvested, and contribute to the distinct tastes found in various types of beer.

Pick Window

The science and art of harvesting hops are governed by a critical period known as the “pick window.” This is the fleeting moment in time when the hops reach their zenith in aroma and flavor, ready to be harvested and utilized to their full potential in the brewing process. The complexity of the pick window is profound, and it requires a combination of experience, observation, and precision from hop growers.

The pick window is not universal; it fluctuates between different hop varieties and even within distinct regions. The specific characteristics of the soil, climate, and weather patterns can cause these windows to shift, sometimes dramatically. They are excruciatingly narrow, often spanning only a few days, and this adds an additional layer of challenge to the task.

The significance of this short window cannot be overstated. Being even slightly early or late can transform the very essence of the hops. Take, for example, the Centennial variety, renowned for its floral and citrusy notes when picked at the precise right moment. Harvest it too soon, and its flavors become grassy and muted, losing their vibrancy and complexity. Wait too long, and the profile alters entirely, resulting in an oniony and garlicky or “OG” flavor, a far cry from its intended character.

The stakes are high, and the margin for error is slim. Growers must perfectly synchronize the start and finish of the harvest with the natural rhythms of the plants to capture their essence. They rely on a blend of sensory analysis, evaluating field samples through smell and taste, alongside rigorous laboratory data. The science meets the senses, and together they guide the growers in pinpointing the exact time to harvest.

 Leaf, Stem, and Seed

Once the hop bines have been harvested, a meticulous evaluation process commences, where samples are selected and assessed for various attributes, including leaf and stem, and, most notably, seed content. This scrutiny is not merely a routine examination but a crucial step that can significantly impact the subsequent brewing process.

The growers play an active role in ensuring the quality of the hop cones. Throughout the growing season, they have the opportunity to take measures that reduce seed content, a key aspect in determining the hops’ value in brewing. One effective method is the systematic removal of rogue male hop plants from the production area each season. This vigilance in eliminating male plants is more than mere tidiness; it’s a targeted strategy. Seeds, after all, offer no benefit to the brewer. In fact, they are regarded as completely irrelevant in the brewing process, an element that does not contribute to flavor, aroma, or any other sought-after quality.

Hop lots with minimal or no seed content are generally seen as more desirable, embodying a standard that reflects both purity and potency. This preference for seedless hops is not a trivial matter but a consensus that has evolved within the brewing community, recognizing the clear advantages of such hops in crafting superior brews.

After the harvesting of the hop bines, they are channeled through specialized machinery known as hop harvesters or “pickers.” These machines are marvels of engineering, designed to perform a delicate yet efficient separation of the hop cones from the associated plant material, such as leaves and stems. The precision of this separation process is essential, and a high-quality hop-picking operation is judged by its ability to consistently produce lots devoid of any leaf and stem content.


Once the hops have been harvested, the next pivotal step in their journey to the brewing vats is the drying process. This is carried out in specialized kilns, designed to extract the excess moisture content that is present in the freshly harvested hops. There are two primary elements at play here that define the success of the drying process: the temperature at which the kiln is operated and the depth of the hop bed.

The temptation might be to run deep hop beds through the kilns at elevated temperatures. This would allow growers to expedite the process, handling a greater volume of hops in a shorter time. However, this approach is fraught with risks that can negatively impact the quality of the hops.

High temperatures, while effective at driving out moisture, can have the undesirable effect of reducing the essential oils that define a hop’s unique aroma and flavor profile. These oils are the soul of the hop, contributing to the signature characteristics that brewers seek. Losing them means compromising the very essence of the hop, something that could reflect in the final product.

Over-stacking the kiln is another peril. A deep bed might seem efficient, but it can obstruct the drying process. This leads to uneven drying, where some portions, especially the bottom layer of the kiln bed, might become overdried. This unevenness can again lead to a loss in quality, creating an inconsistency that is unwelcome in a process that demands precision.

 Baling Process and Bale Receiving

The procedure for handling kilned hops requires meticulous care, underlining the importance of quality control in the creation of beer. This process begins with a crucial cooling phase, where the kilned hops are ideally allowed to rest for a minimum span of 24 hours. This conditioning period serves a vital function in ensuring the uniformity of moisture content within the hop lot, thereby fostering the production of a more consistent and higher-quality baled hop product.

Once the conditioning phase is concluded, the hop lots are compressed into bales, a form that readies them for storage and eventual processing. At this juncture, measures must be taken to slow down the natural process of degradation that can adversely affect the hops. While freezing the hop bales is the optimal storage method, the scarcity of freezer space often leads some growers to store bales in cooler, dark areas or even at ambient temperatures. Although these methods may be more practical, they might also accelerate the degradation process, potentially leading to a diminished quality of the end product.

Upon receipt of the hop bales, the processor must undertake a rigorous inspection process. This includes measuring both the temperature and moisture content of the hops and taking samples for comprehensive sensory analysis and laboratory testing. The visual inspection also plays a crucial role, enabling the detection of any defects such as mold, excessive pest damage, or issues related to cone integrity.

Should any of the hop lots or individual bales fail to meet the required standard, they will be rejected by the processor. This stringent approach underscores the non-negotiable emphasis on quality within the brewing industry.

Following these inspections, the bales should be immediately frozen, thus preserving their integrity until they can be processed. Maintaining a consistent temperature during this period is essential, serving to safeguard the quality and consistency of the hops.

Pelletized Hops Processing

Vacuum sealing and pelletizing hops have become common practices in the brewing industry. This method appeals to brewers because it allows for extended storage life, occupies less space, and simplifies handling during brewing. Recognizing the market’s preference for this format, numerous hop growers and processing companies have invested in specialized equipment for pelletizing and vacuum sealing.

There are two primary types of hop pellets, designated as T90 and T45, that are processed differently and serve distinct purposes.

T90 Pelletized Hops — The “T90” label signifies that 90 kilograms of pellets are produced from every 100 kilograms of dried hops. These pellets undergo a process that includes the separation of unwanted materials and foreign ingredients following homogenization. The product is then dried to achieve a moisture content between 7–9%.

Once prepared, the T90 hops are ground into powder and granulated into pellets with a diameter of 6 mm. These pellets are packaged in aluminum foil bags filled with an inert gas mixture of nitrogen and carbon dioxide, typically in cartons containing four 10 kg bags. The resultant T90 granulated hops retain characteristics closely analogous to cone-shaped hops. However, they offer advantages such as more efficient utilization of brewing substances, extended shelf life, and greater ease in storage, handling, and transport.

T45 Pelletized Hops — The T45 pellets follow a more complex process, resulting in a more concentrated product. The 45 refers to the yield of 45 kilograms of pellets from 100 kilograms of dried hops. Unlike the T90, the T45 process concentrates the lupulin, giving it a higher lupulin-to-weight ratio and requiring less quantity in brewing compared to T90 pellets.

The processing of T45 pellets occurs at a temperature of -35 °C, where the hops are ground into powder. The lupulin is then separated from the vegetative part using vibrating screens, and a standardized product is created by carefully mixing precise ratios of lupulin and vegetable parts. This results in a product with a predetermined content of alpha-bitter acids. Like the T90, the T45 pellets are granulated and packed into aluminum foil bags. The T45’s higher concentration of hop resins and predetermined alpha-bitter substance content offers the advantage of simplified dosing in the brewing process.


The management of hop varieties is a meticulous and time-sensitive process due to the inherent variation in the rate at which different hop types degrade. Processors must act with precision and foresight to orchestrate a processing schedule that prioritizes the more perishable varieties. Though cold storage offers a temporary solution to extend the freshness of hops, it’s far from a foolproof strategy.

Take, for example, the Centennial and Idaho 7® hop bales. Even under the preservation of frozen storage, these specific varieties are known to deteriorate more rapidly than others. Their characteristics demand prompt processing to retain the quality and flavor that make them valuable to brewers. Any undue delay in handling these hops can lead to a loss in their unique properties, impacting the final product they are intended for.

On the other hand, varieties such as Nugget are known for their superior storage attributes. These hops are more forgiving in terms of processing timelines, allowing them to be safely left until the latter part of the pelleting season. Their resilience in storage offers greater flexibility in scheduling, which can be strategically leveraged to optimize the overall processing workflow.

In essence, the careful planning of the processing schedule is a balancing act that requires an in-depth understanding of the properties of each hop variety. It’s not merely a logistical challenge but a crucial aspect of quality control that impacts the flavor profiles and integrity of the beers they will become a part of.


In processing raw hops to finished pellets, temperature control emerges as a vital constant, demanding rigorous monitoring at every stage. It’s a delicate balance, where each step contributes a subtle addition of heat, and this accumulation can significantly impact the final product’s quality.

The raw hops initially pass through a hammermill, a crucial phase where the leaves are transformed into hop powder. This isn’t merely a mechanical operation but an intricate dance where factors like screen size, residence time, and, most importantly, temperature management converge. These variables must be orchestrated with precision, for the hammermill’s function is not just size reduction but a foundational step that sets the tone for everything that follows. Any deviation in this stage can ripple through the process, affecting the texture, quality, and efficacy of the finished pellet.

The next stage where the hop powder is forced through the pellet die to shape the pellets introduces another layer of complexity. The friction inherent in this stage generates additional heat, which, if unchecked, can spell disaster. The fragility of the oils essential for the hops’ expressive character requires a vigilant eye on the temperature gauge. If the heat escalates to critically high levels, these vital oils may be lost, stripping the hops of their essence.

Hop pellets that have suffered under excessive heat bear the scars in their appearance, often manifesting as a glassy or shiny texture, sometimes even showing a burnt look. Such visual indicators are warnings, evidence of a process that slipped out of the narrow band of acceptable conditions.

To mitigate these risks, processors are tasked with a non-negotiable directive: the temperature of the hop material must be maintained below 125°F throughout the entire production process. This temperature threshold is not arbitrary but a carefully defined line, a safeguard against the loss of those elements that make hops indispensable in brewing.

Pellet Consistency and Density

In the brewing process, the transition from leaf hops to pellets must be undertaken with extreme care and precision, for even the finest quality of leaf hops can fall prey to the pitfalls of poor pelletization. The conversion of hops to pellets is a complex process and requires a deep understanding of the attributes that define the hops’ character.

Processors often mix various hop lots to produce a single batch of pellets, a delicate operation that requires keen insight and careful control. Understanding and quantifying the sensory characteristics and attributes of the input lots is crucial. It’s not merely about blending; it’s about achieving a homogenous blend that meets the exact specifications needed for brewing. Thus, the pelleting facility must have the proper blending capacity, ensuring consistency across the entire lot.

Monitoring and measurement are key to this high-quality process. Real-time analytics provide the assurance that the finished product adheres to the desired standards. This includes paying attention to the density of the pellets, a factor that significantly impacts their interaction with the beer.

High-density pellets, though firm, may sink to the bottom of the tank, thus losing the opportunity to infuse the beer with their flavor and aroma. Conversely, low-density T-90 pellets are known to disperse more rapidly and remain suspended longer, thereby enriching the brew with more of their essence. However, too low a density can lead to crumbling in packaging or floating on top of the liquid during dry hopping, issues that compromise the brewing process.

The difference in density can be physically felt. High-density pellets might break when handled but generally maintain their solid form. The ideal pellets, with proper density and particle size, break up into a loose grind, thereby enhancing the dispersion of hop flavor and aroma during brewing. Uniformity in density is essential, and every pellet in a lot should meet this criterion.


Oxygen, light, and heat stand as the formidable adversaries of hops, capable of compromising the quality and flavor that are so essential in the brewing process. In order to preserve the integrity of the hops after they have been processed into pellets, meticulous care must be taken in their packaging and storage.

The pellets ought to be securely enclosed in resilient, light-resistant foil bags, specially designed to shield the hops from their external enemies. This alone, however, is not sufficient. To eliminate the presence of oxygen – a subtle yet pernicious threat to quality – the bags must be flushed with inert gases such as nitrogen or carbon dioxide. This process replaces the air within the packaging environment, thereby minimizing the risk of oxidation and the consequent deterioration in flavor and aroma.

This encapsulation in a carefully controlled atmosphere is only part of the preservation strategy. Quality control processes need to be robust and responsive. The processor must adopt rigorous protocols to regularly assess the integrity of the package seals, as well as to monitor the residual oxygen levels within. This requires a commitment to precision and consistency, recognizing that even a minor breach or oversight can undermine the very essence of the hops.

Once the packaging has been securely sealed and subjected to stringent quality checks, the hops must be promptly returned to a cold environment. Storing them in a freezer as soon as possible ensures that the natural enemies of heat and light are kept at bay. By maintaining a controlled, low-temperature environment, the hop pellets are cocooned in a state of stasis, their qualities preserved until they are summoned to fulfill their role in brewing.

Pelletized Hops Alternatives

Whole Flower Hops:
Whole flower hops refer to the dried blossoms of the hop plant. Traditionally, these were dried in a specialized building called an oasthouse, usually consisting of two or three stories. Within the oasthouse, the hops were spread across the drying floors above a wood- or charcoal-fired kiln on the ground floor. These floors were thin and perforated, allowing heat to circulate through the hops and escape via a cowl, an angled chimney situated in the roof. Modern practices have replaced this traditional method with more industrial drying techniques. This change in process has led to many oasthouses being repurposed into private residences, reflecting a shift in technology and culture.

Fresh Hops:
Fresh hops are the green, unprocessed cones harvested directly from the hop plant. Unlike their dried counterparts, fresh hops are often added to the beer within just hours of being picked. These wet hops imbue the beer with a bright, intense hop flavor and aroma. However, the fresh hops lack the concentration found in dried hops, requiring a much larger volume to achieve the desired flavor and aroma. The additional vegetative matter can also give the beer a grassy character, leading to greater wort loss for the brewer. It’s a delicate balance that reflects the nuances of using fresh ingredients in brewing.

Hop Extracts:
Hop extracts represent a more refined application of the hop’s essential components. Here, alpha acids and essential oils are extracted from the hop cones using heat and various solvents. These liquid concentrates can be used in brewing just like traditional hops but in a more concentrated form. Hop extracts are categorized for different purposes, such as bittering, flavoring, and adding aroma. Predominantly used by large breweries, hop extracts offer ease of storage and longevity without spoilage. They also reduce the amount of material needed and eliminate wort loss. The concentrated nature of hop extracts can make them challenging to use in small batches, and some brewers have expressed concerns about potential undesirable flavors.

Pressed Hops:
Pressed hops are a common and practical form of hop processing. Following the drying and homogenization process, any undesirable hops and foreign materials are separated. The hops are then dried to the required moisture level, typically around 10–12%. Once prepared, hydraulic presses are used to form the hops into rectangular bales or ballots, typically weighing between 100–150 kg.

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