Hop: An Emerging Crop in Subtropical Areas in Brazil

Abstract

Brazil is one of the three largest beer producers in the world. Four basic ingredients are needed as raw material for the production of beer: water, malt, yeast, and hops (Humulus lupulus L.). Until recently, almost all of the hops in Brazil were imported from other countries. However, in the last decade, hop cultivation in Brazil has emerged due to the increase in the number of new craft breweries, which have demanded diversified raw material for the production of various types of beer. Hops is considered a short-day, temperate species, so the major challenge for the development of hop cultivation in Brazil, with high-yield capacity and with local typicity of bitterness and aroma, is the adaptation of cultivars to the photoperiod conditions in subtropical regions. This review addresses the history of hop cultivation in Brazil and characterizes the main climatic elements of three emerging subtropical growing regions located at different latitudes, such as air temperature, photoperiod, solar radiation, and water availability, to provide support for the development of new technologies for hop cultivation, including supplemental lighting, irrigation, and mulching.

1. Hop Production and Economic Importance

Hop (Humulus lupulus L.) is a dioecious twining herb of ancient domestication and use, found in the wild throughout almost all temperate climate ranges [1]. It is a perennial species that annually produces inflorescences, over an approximately four-month season [2]. The female flowers develop in cones, also known as strobiles, which are responsible for adding bitterness, aroma, and microbiological stability to beer. Hop is one of the essential raw materials for beer production worldwide [3] and, to a lesser extent, is used in the pharmaceutical industry [4].

Each hop cultivar has different levels of aroma and essence in its composition, and the compounds of interest to the brewing industry are the levels of alpha and beta acids and the essential oils present in the cones of the hops [5]. Hops can be marketed in various forms: fresh, dehydrated, powdered, and extracts. In the brewing industry, the most commonly used form is pellets. In addition, hop is an essential raw material for the characterization of brewing products in the modern brewing industry. In addition to giving beer the typical bitter and aromatic flavor, hop is an important cofactor in several processes of stabilization of the finished product. Due to the reaction between bitter acids and wort proteins, hop allows for the clarification of beer, stabilizes foam, and is also a natural preservative [6].

Hops are one of the most important components the brewing industry and, although they are used in relatively small amounts, they account for a large percentage of the cost of production [7]. Based on the type and amount of hops, it is possible to produce a variety of beer with different aromas and degrees of bitterness [5].

The world’s largest beer producers are China, the United States, and Brazil [8], and the demand for a diversified range of quality hops has been growing in industries around the world. In Brazil, beer production is approximately 15.3 billion L year⁻¹ and represents 1.7% of the national GDP, with annual revenue of BRL 160 billion, and is one of the most important sectors in the Brazilian economy [9,10]. However, Brazil imports almost all of the hops used in the production of beer, and in 2020, 3243 tons were imported, mainly from the United States and Germany, for a total of USD 57 million [11].

Hops are commercially produced in more than 20 countries, mainly in temperate regions between latitudes 35° and 55° N or S of the Equator (Figure 1), with the regions of Hallertau in Germany and Yakima in the United States being the most important, together representing 77% of world production. In 2020, global hop production was 122 thousand tons in an area of 62,366 ha [8,12]. The United States stands out as the world’s largest producer, with approximately 47,540 tons on 24,738 thousand ha, which corresponds to 40% of the total produced, generating USD 637 million. Germany is the second largest producer, with 46,878 tons in an area of 20,706 ha, which corresponds to 33% of the volume produced. In the last 10 years, the increase in the volume of hop production and the planted area in the world was approximately 45% [12,13].

In some production databases, Ethiopia has been considered an important hop-producing country; however, Ethiopia produces Rhamnus prinoides (not H. lupulus), an African shrub or small tree in the family Rhamnaceae, commonly referred to as gesho. It is used in a manner similar to hops in the brewing of tella, an Ethiopian beer prepared from honey, water, and the leaves of gesho [14].

More recently, the dynamics of global trade have greatly encouraged the expansion of hop-growing areas, now spanning between 35° and 55° parallel to both hemispheres [15], especially in Australia, New Zealand, South Africa, Argentina, and Brazil [16].

Hop cultivation in Brazil has been driven mainly by the increase in a large number of new craft breweries, which have demanded diversified raw material for the production of various types of beer. In 2020, 1383 new breweries were registered in the Ministry of Agriculture, Livestock, and Food Supply, which corresponds to a growth of 14.4% compared to 2019, and 80% are located in the South and Southeast regions of the country, between latitudes 20° and 30° S [9].

Although there are reports of attempts to grow hops in Brazil in the 19th century when the country was still a colony of Portugal, its commercial production only started to be important in 2016, when several cultivars were imported and registered by commercial nurseries with authorization from the Ministry of Agriculture, Livestock, and Food Supply, which later began to multiply and provide healthy nursery plants of high genetic quality [17].

Interest in cultivation in Brazil has increased with the influence of adapted technologies, the manipulation of the species by crossbreeding for genetic improvement, and the possibility of adaptation to local conditions [18]. This escalation of interest, both in the cultivation and commercial exploitation of hops, has attracted important investments for its establishment on the national level. Although still in the development phase, hop production has interested several entrepreneurs, mainly in the south and southeast regions of the country [16,19].

The major challenge for the development of hop production in Brazil is the adaptation of cultivars to the local geographic and climatic conditions. High yield capacity and local typicity of bitterness and aromatic flavor are two desirable features to meet the growing demand for raw material by the brewing industry in Brazil. In this review, we address the main characteristics of hop cultivation in Brazil, such as the history, introduction, plant use, adaptation of cultivars, and cultivation techniques, as well as analyze and discuss the main climatic elements that influence its cultivation in emerging subtropical regions of different latitudes. To the best of our knowledge, no such data has been published up to date, and it could serve to encourage growers and pharmaceutical industries to promote the cultivation of hops as a novel multipurpose crop in the country.

2. Hop Growing in Brazil

The first reports of hop cultivation in Brazil date back to 1885, when Emperor Dom Pedro II brought seedlings to cultivate in the state of Rio de Janeiro. There are also reports from 1869 of the introduction of seedlings brought by Polish immigrants to the state of Paraná. Decades later, in approximately 1953, the Austrian immigrant Roland Hoblik planned to cultivate hops in Nova Petrópolis in the state of Rio Grande do Sul, but cultivation of the species failed to prosper when the local breweries that supported its production were acquired by a larger brewery that imported this raw material from other countries [17], and the activity was discontinued. Other isolated attempts at cultivation were also carried out later in the early 1980s at the Instituto Agronômico do Paraná, but without success.

In the mid-2000s, attempts to cultivate hops resumed in Brazil. A grower in the state of São Paulo started to grow hops plants from seeds imported from Canada, but he had no success and decided to remove the plants. In 2005, one of the plants that had been removed naturally regrew and developed in the field, completing its full life cycle. Subsequently, this plant multiplied and the cultivar was given the name Mantiqueira. This sparked interest in imminent production in several locations in the country [20].

By 2010, the cultivation of national hops became more important, driven by the growing number of craft breweries in the country which demanded diverse raw material for the production of different types of beer. This resurgence motivated several entrepreneurs to invest in new cultivation areas due to the availability of new technologies developed by some research institutions [19,21,22]. Among these technologies, the use of supplemental lighting from LED lamps to control the flowering of plants in the field stands out. No regions of Brazil otherwise meet the minimum requirements for the hop photoperiod, specifically that of regions between latitudes 35° and 55° North or South of the Equator (Figure 1), and this was one of the main causes of the failure of hop cultivation in the country previously.

It is noteworthy that the national hop demand was also influenced by the search for freshly harvested and dehydrated raw material, requiring shorter storage time, as the hops lose quality in the pelleting process due to oxidation and degradation of their chemical compounds over time [5].

Given the growing interest in hop cultivation in Brazil, in 2018, the Brazilian Association of Hop Producers—APROLÚPULO—was founded in association with the University of State of Santa Catarina, UDESC, Lages, in the state of Santa Catarina, with the objective of gathering information and promoting hop cultivation in the country [18]. Additionally, in 2018, a network was formed for the promotion of hop cultivation in the Região da Serra Fluminense, in the state of Rio de Janeiro, bringing together several public research institutions and private companies to share knowledge and resources so that hop cultivation could become a viable activity.

The main Brazilian hop production initiatives are spread over 50 ha in regions of different latitudes and climates, especially in the southern region of the country [16]. For this reason, this region has the highest concentration of hop producers and craft breweries in the country, and the state of Santa Catarina has the largest number of producers, specifically in the Lajes region (latitude 28° S). Other hop production initiatives have also been carried out in other regions in the south of the country, such as in Palotina, in the state of Paraná (latitude 24° S), and in the southeast region, including Ribeirão Preto (latitude 21° S (Figure 2), whose main climatic characteristics will be summarized later in this review.

Thus, the hop production chain in Brazil represents the integration of different sectors, and several studies have been carried out, among which the following topics stand out: adaptability of cultivars; breeding; training systems; supplemental lighting; irrigation and fertilization management; disease and pest control; economic and feasibility studies; and methods of chemical evaluation of cones and quality for the brewing industry [4,17].

In addition, due to the climatic conditions in Brazil, the possibility of more than one production cycle per year was explored in some regions, while in regions following traditional cultivation practices, only one cycle is obtained per year [19]. This is a differential that can further enhance hop cultivation in the country, similar to the state of Florida, US [23], whose climate is also subtropical and situated at latitude 31° N.

These hop cultivation initiatives in Brazil have generated great enthusiasm for the production of this important raw material for the brewing industry. In addition, Brazilian hops have shown distinct characteristics in terms of bitterness and aroma when compared to imported products, which have led to the production of beer with typicity [5,24], which has been the focus of several initiatives in the country.

Brazil has great potential for the development of hop cultivation, and the interest in expanding the production chain has led to the union between public research institutions and private companies, such as AMBEV (Americas’ Beverage Company), with the aim of generating, expanding, and disseminating knowledge about the production of high-quality and sustainable raw materials in the country [25].

3. Botanic Characteristics and Hop Cultivars

The genus Humulus consists of three species, Humulus lupulus, Humulus japonicus, and Humulus yunnanensis, with H. lupulus being the main commercially cultivated species used by the brewing industry because of its high levels of lupulin [16,26].

Hops are climbing, herbaceous, and perennial plants belonging to the Cannabaceae family. They are a dioecious plant, developing male and female flowers on separate plants [27,28]. However, only female plants are cultivated on a commercial scale, since female flowers, called cones or strobiles, have a higher yield of resins. The flowers of the male plant have only 10–15 lupulin-secreting glands, while the female flowers have 10,000 or more glands [16]. Thus, male plants, which are easily distinguished from females, are only important for breeding and are used to develop new cultivars in controlled crosses [29] but should not be used for commercial production in the field.

The resins produced in cones originating from female flowers are characteristic of hops are not found in any other plant species. The resins are produced in lupulin glands present in the trichomes of the bracts of the inflorescences [20].

Lupulin-secreting glands have the ability to synthesize and store resins and essential oils due to the presence of more than 300 aromatic compounds. Essential oils are formed mostly by hydrocarbons [4], phenolic terpenes, and polyphenols [30]. Terpenoid compounds, including alpha acids, also known as humulones, serve as a source of flavors and aromas, while beta acids, or lupulones, produce wort biostasis [31]. In resins, the percentage of alpha acids, beta acids, and essential oils varies between 3 and 17%, 3 and 7%, and 0.5 and 2%, respectively [16].

Alpha acids contribute to beer bitterness and act as bacteriostatic agents, favoring the action of yeasts during the fermentation process and inhibiting the action of some bacteria. Alpha and beta acids start to accumulate in cones from the beginning of the flowering stage [27].

Essential oils are chemical compounds related to the aromatic components of different cultivars and provide aroma to beer. The groups to which these compounds belong are the monoterpenes (myrcene, limonene, and alpha-pinene), sesquiterpenes (farnesene, humulene, and beta-caryophyllene), and terpene alcohols (linalol) [5].

The chemical composition of hop cones depends on the genetic factors of the different cultivars, harvest points, and climatic and geographical conditions [32]. The concentrations of these compounds are largely dependent on the age of the plant, the cultivar, and the soil and climate conditions associated with the cultivation location [33]. The yield increases until the third year of the plant’s life, when they tend to stabilize, and in the first two years, their quality is lower [34].

The cultivation of hops for use in beer production originated in the Northern Hemisphere, starting in Eastern Europe around Bohemia, Slovenia and Bavaria before the XIII century, then spreading to other European countries [16]. In addition to the characteristic bitter and aromatic flavor, hops became known for their conservation properties in beer, as opposed to the combination of herbs, flowers, fruits, roots, bark, and even vegetables, known as gruit, which were added to the beverage for these purposes [4]. Thus, in 1516, in Bavaria, Germany, the Purity Law was created also known as Reinheitsgebot, in which only hops could be added to impart bitterness in beer [20]. In 1629, European hops began to be introduced in the United States, and soon cultivation of the plant spread to the south and west of the country; however, it was only in the 1800s that production on a larger scale was successful [29].

Starting in the 1800s, the British introduced the crop in their southern hemisphere colonies, such as in South Africa, Australia, and New Zealand. In approximately 1860, the Germans introduced hops to China and Korea, and in 1876, with the popularity of hop beer, the Japanese began to produce American and German cultivars. Finally, hops arrived in South America in 1851, brought by a Chilean diplomat who started their commercial cultivation in Chile in 1857. Later, German immigrants living in southern Chile introduced hops in Argentina in 1865 [20].

Hop cultivars differ according to their country of origin, morphological characteristics, maturation periods and chemical composition [35], especially in relation to the quantity of alpha and beta acids and essential oils [36]. Bitter cultivars are characterized by having higher levels of alpha acids in their chemical composition [5].

There are currently more than 260 cataloged hop cultivars, each with different characteristics appreciated by the brewing industry in terms of bitterness, aroma, and flavor [35]. However, the most abundantly cultivated cultivars worldwide include approximately 30 American and 40 European cultivars, with a smaller number of Asian cultivars.

The hop cultivars with the largest production area in the US today are Citra^®, Mosaic^®, Simcoe^®, Cascade, Centennial, and CTZ (an acronym for Columbus, Tomahawk, and Zeus, three trade cultivars owned by various private corporations for the same cultivar of hop) [12], while in Germany, the most important cultivars are Perle, Hallertau Tradition, Hallertau Magnun, and Herkules [8].

In Brazil, there are 48 hop cultivars registered in the Ministry of Agriculture, Livestock, and Food Supply, the most abundantly cultivated currently being Cascade, Columbus, Chinook, Nugget, Saaz, Centennial, Comet, Hallertau, Hallertau Mittelfrüher, Mapuche, Magnum, Zeus, Fuggle, and Northern Brewer [9]. An important impetus for the increase in new hop areas in Brazil was the establishment of commercial hop nurseries, such as Ninkasi, Hops Brasil, Van de Bergen, and Lúpulo Gaúcho, which have provided a supply of female nursery plants of different cultivars and of high genetic quality, multiplied via cuttings.

4. Hop Training

Hop plants develop from rhizome twining stems called bines, which climb with the help of stiff hairs along their stems known as trichomes. Hop bines grow rapidly, with a peak growth of up to 25 cm per day [4,37]. Because of this climbing growth behavior, commercially grown hop plants in Brazil are trained to grow up on high trellises created from different materials, such as coir twines or cotton strings (Figure 3), typically 5 m tall.

When hops are growing, they go through two stages, the vegetative phase (early season) and the flowering or reproduction phase (late season). The early season is the time for hop plants to reach the top of the trellis to develop ample sidearms for cone development in the late season.

Hops have strong apical dominance and indefinite growth, reaching lengths of 6–8 m. The leaves appear opposite the nodes, petiolate, heart-shaped, with 3 or 5 lobes, and with serrated and rough edges with a pointed apex. Secretory trichomes, or glands of resins and essential oils, are found on the underside of the leaves [20].

Hops are trained in very high trellis systems, so it is essential that windbreaks are installed around the hopyard, because winds can cause the plants to fall, and reduce cone quality.

Training hop bines is a laborious task that involves manually wrapping the bines around a cotton string in a clockwise direction to encourage vertical growth. Second-year hop plants are generally productive enough to be trained with 2–4 strings per hill, depending on planting density and hopyard layout. Crowns produce a multitude of bines during regrowth, and early vigorous growth tends to be rigid and brittle and can result in bines with long internodes that are not conducive to maximizing yield; for this reason, bine selection is critical. By selecting more uniform and secondary shoots, the crop load can be increased and the risk of bines breaking in wind events can be reduced. Succulent bines must be selected, with 2–4 bines per string, depending on the cultivar [38].

5. Hop Climatic Requirements

Hops are traditionally cultivated in temperate regions [33], but in the Southern Hemisphere, the main production regions are located in Australia between 37° and 43° S, in New Zealand between 41° and 42° S, in Argentina between 35° and 40° S, and in South Africa at 34° S [29].

Climatic conditions play a decisive role in the cultivation of this species, with air temperature, photoperiod, solar radiation, and water availability being the main considerations. Since hops cultivation began only recently in Brazil, a large country with varied terrain, knowledge of the climate in the different regions becomes essential for the determination of the most appropriate areas for hops cultivation, as well as for the choice of cultivars and for the utilization of cultivation techniques, such as the timing for cut back and harvesting and the use of supplemental lighting, chemical fertilization, and irrigation.

Thus, in this review, the main climatic elements of three emerging regions in Brazil of different latitudes are summarized as follows: Lages, Santa Catarina state (latitude 28° S, 50° W, elevation 916 m a.s.l., Cfb climate, humid subtropical with temperate summer); Palotina, Parana state (latitude 24° S, 54° W, elevation 320 m a.s.l., Cfa climate, humid subtropical with hot summer); and Ribeirão Preto, São Paulo state (latitude 21° S, 48° W, elevation 516 m a.s.l., Aw climate, tropical with dry winter) (Figure 2). The aim is to generate information so that the production of quality raw material for the brewing industry can be implemented efficiently and sustainably in the country. More adapted and suitable hop cultivars are grown in each of these three locations, and the high trellis training system used is similar among them. Because of the recent hop cultivation in the country, is it not known yet if there are any distinct differences in beer styles that predominate in each region.

Therefore, we analyzed the monthly average and minimum temperatures (°C) and precipitation (mm) of each location obtained from the GEE Platform of the FLDAS product, Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System, and from Copernicus Climate Change Service (C3S) Climate Data Store (CDS) Plataform [39,40]. A 25 km buffer was generated around the regions of Lages, Palotina, and Ribeirão Preto to obtain monthly data from 1982 to 2021. The historical monthly averages of temperature were calculated for each buffer.

We also analyzed the photoperiod, the day length (hours), of each location. Calculations were performed by using the equation: N = 2/15 arcsin (-tan φ * tan δ), where N = length of day in hours; φ = geographic latitude (negative value for the southern hemisphere); and δ = solar declination, which was calculated using the equation: δ = 23.45.sin [360(284 + n)/365], where n = the Julian day of the year [41]. Values were transformed into radians for sin and tangent calculations.

Finally, we generated insolation (W/m²) graphs of each location from an adaptation of MATLAB code provided by Johns Hopkins University [42] using the following equation: W = S0 r⁻² (sin φ * sin δ + cos φ * cos δ * cos H), where W = insolation in W/m², S0 = solar constant, r = Earth–Sun distance, z = distance from zenith, φ = geographic latitude, δ = solar declination, and H = hour angle.

In traditional growing areas, air temperature is an important climatic element for the production of hops, and it greatly influences the timing of the initiation of the growth of plants after the winter, which determines the harvest season of cones [43]. At the end of winter, the average air temperature must gradually increase and reach 10 °C for the plants to start their vegetative growth. The hop plant depends on an ideal temperature range between 13.2 and 20.5 °C during the spring and summer seasons for its development, and hops stop growing below 5 °C and above 35 °C [33].

In high latitude regions of Brazil where the winter season (July September) is more severe and lasts longer, such as in Lages (latitude 28° S) (Figure 4), cut back hops tend to regrow from mid-September (early spring), and cones are harvested from February to early March (late summer) of the following year, with the exact timing depending on the cultivar. On the other hand, in regions with mild winters, such as Palotina (latitude 24° S) and Ribeirao Preto (latitude 21° S), which has a low risk of frost, cut back hops regrow from late July (mid-winter), and cones are harvested in mid-December (early summer). This is interesting from the point of view of maximizing crop production in these regions, since after harvesting, it is technically possible to induce a second production cycle by applying a second cut back, and the air temperature remains high until late April, allowing for good vegetative development of the plants.

However, there are some limitations to obtaining two production cycles in higher latitude regions regularly, especially because of low minimum air temperatures (<10 °C) that frequently occur from early May to early September (Figure 5), not allowing enough time for hops to complete a second production cycle before mid-April. In lower latitudes, such as in Ribeirão Preto (21° S), high average temperatures between July and August are characteristic of a tropical climate, but in this period, the precipitation is very low, requiring supplementary irrigation most of the year.

The distribution of rainfall throughout the year also influences hop cultivation. The water requirement may vary according to the growing region, as the demand for hop evapotranspiration depends on temperature, wind, air humidity, and soil type [44]. The average temperature of Lages is lower than that of the other regions, resulting in lower evapotranspiration.

In the hottest seasons of the year, the water requirement is higher, and precipitation may be insufficient in regions with low or medium rainfall, requiring the use of irrigation, especially during phenological stages with a higher demand for water, such as the flowering stage [29], when the plant absorbs large amounts of nutrients and water. The average rainfall required is 500–600 mm during hop vegetative growth, and the precipitation must be evenly distributed throughout the period in order to achieve greater cone yields [27,44].

In the Lages region, the distribution of rainfall throughout the year is the most uniform of the three locations, without the occurrence of dry periods (Figure 6), which is ideal for good hop development. Rainfall tends to decrease in the Palotina region during the winter season between July and August, but without the occurrence of a water deficit. However, in Ribeirão Preto, there is a clear lack of rain during the winter, with well-defined dry periods from April to September. The use of mulching in the hopyard in Ribeirão Preto is a practice that helps maintain the water in the soil, increasing the efficiency of irrigation. Nevertheless, in Ribeirão Preto, the rainfall is high in the summer, from December to February, which explains the lower air temperatures in this period when compared to those in the Palotina region (Figure 4).

However, irrigation has been mandatory for most of the emerging hop growing areas in Brazil, especially during the early season, even though the amount of rain throughout the year is considered sufficient. During this season, an ample supply of water is essential to allow the bines to reach the top of the trellis properly.

Based on these historical rainfall patterns, the use of irrigation is necessary to provide the water requirement of hops, especially during the early growing season in regions of lower latitudes, such as in Palotina (24° S) and in Ribeirão Preto (21° S), where rainfall is less frequent. Drip irrigation with single or double lines, on the ground surface or suspended, has been the most frequently used system in Brazil. The irrigation schedule is a very important factor, as the highest water demand of plants occurs in periods when evapotranspiration is at its height. Irrigation in periods when plant demand for water is lower can lead to waterlogging of the soil and provide favorable conditions for the occurrence of diseases, especially in the root system. The use of mulch in planting rows, along with a screen or plastic cover, can provide better conditions for protecting the soil close to the hop roots, and allow for better weed control and greater efficiency in the use of irrigation water by reducing evapotranspiration.

The photoperiod is of great importance for determining hop growth and floral induction, defining its cultivation potential [29]. Many plants use day length as an environmental cue to control the timing of flowering [45]. Such plants are classified as short-day or long-day plants depending on whether they flower when the day length becomes shorter or longer than a specific number of hours, referred to as the critical day length [46,47].

Hops are considered a short-day plant, with better flowering efficiency and production when the plant receives more hours of light during the early season [44,48]. When the day length starts to increase, the hops remain in vertical (upward) growth during the early season, and bines expand with sidearms that will bear the crop. When the day length begins to decrease, the plants shift to the reproductive growth phase or late season, when burrs emerge and cones develop, what is a determining condition for obtaining high yields [49]. During the early season, if the photoperiod conditions are not sufficient for vegetative growth, an insufficient number of nodes are formed, which reduces the ability of the plant to bloom later in the season, and cone production decreases.

Day length is important because it is beneficial to maximize vegetative growth before flowering occurs. Hops need more than 15 h of daylight during the early season and less than 15 h of daylight in the late season. When the length of daylight is longer than 15 h in the early season, only vegetative growth is stimulated, and the crop does not flower. Once the length of daylight drops below 15 h in the late season, flowering starts to occur [23].

In addition, Thomas and Schwabe [48] found that the vegetative growth of hops ceases entirely if plants grow under very short photoperiod conditions (<8 h), and that interrupting darkness with flashes of light for half an hour on short days prevents flowering. These authors also found that low temperatures and minimum hop plant size are key parameters for flowering. Consequently, hop plants with fewer nodes than needed for flowering do not flower under short-day conditions. Based on this, the plant’s maturity for flowering, expressed in number of nodes of plant, changes according to the hop cultivar, and early cultivars require the lowest number of nodes to flower.

In Brazil, the length of daylight reaches less than 14 h in higher altitude regions (Figure 7). As a result, hop plants grown under this day length condition tend to flower prematurely and thus have limited bine growth and cone yields. Comparing the three hop growing locations, the day length throughout the year differs among them. For instance, in higher latitude regions such as Lages (28° S), the day length in the winter season (June–August) is shorter, but from mid to late summer season (December–March), the day length is longer than that in the other locations. This climatic condition was indeed one of the main causes of failure in growing hops in the country in all previous attempts, when techniques to manipulate hop flowering by using supplemental lighting were not available.

Additionally, knowledge of the amount of incident solar radiation that reaches the top of the atmosphere, expressed in W/m² [39], helps with understanding the development of hop plants and expressing the quality of the inflorescences. The Earth’s inclination in relation to the Sun results in different heating conditions between regions. This pattern of greater intensity during the summer and lesser intensity in the winter is shown in Figure 8. For instance, in Lages, the solar radiation during the winter season (≈170 days of the year) is lower than that at the other locations. Another determining factor is latitude; at higher latitudes, the incident solar radiation is lower than at lower latitudes. This analysis contributes to our understanding of the availability of solar radiation during the year and, in combination with the photoperiod, determines the potential for hop cultivation in each region.

These climatic conditions have a strong influence on hop development among these three locations, and different cultivars and technologies are required to grow high-yielding hops. More recently, the use of supplemental (artificial) lighting to control hop flowering and yield was introduced, which can be considered a turning point for successful hop production in subtropical regions, where natural day length induces premature flowering and does not promote adequate bine growth.

The use of supplemental lighting to control hop flowering is still under evaluation in these three locations of Brazil, and some specific characteristics of the light-emitting diode (LED) lamps, such as spectrum, power, spacing, and density, are being assessed. However, in other subtropical regions, such as Florida, US (latitude 31° N), Agehara [23] had good results with effective hop flowering control using LED lamps to induce vegetative bine growth to support higher yields and simultaneously to prevent flowering during the early growing season. In addition, Bauerle [2] also yielded good results manipulating the flowering of hops grown in greenhouses and obtaining multiple crops per year.

One of the main advantages of LED lamps compared to other light sources is the ability to control light spectral composition for specific applications [50]. In addition, it is important to select LED lamps designed to inhibit the flowering of short-day plants, such as the Philips GreenPower LED DR/W 10 W flowering lamp, which offers a combination of deep red and white spectra (DR/W) [23]. In Brazil, several types of LED lamps are under evaluation to increase hop production, including the DR/W and other grow lights within the photosynthetically active radiation spectrum in different layouts. Depending on the climatic conditions of each location, hop cultivar, and other growing conditions, some adjustments are required when supplemental lighting is used to manipulate hop growth. Basically, the lower the latitude of a given region is, the greater the number of hours of artificial lighting required during the early season. However, the air temperature conditions for hop growth of a given location must also be considered.

The LED lights are hung at the top of the trellises spaced at 10 m, so they hang over the hop plants in the upper part of the trellis. When the daylight begins to fade, the LED lights are turned on to simulate the conditions of daytime (Figure 9). The LED lamps are turned on at least half an hour before sunset and remain on for 5–7 h a day, depending on the latitude, to supply a minimum of 17 h of daylight length over 7–9 weeks or until hops develop sufficient vegetative bine growth [2,51].

Hop plants normally begin developing flower buds within a few days after the termination of photoperiod extension. As a result, an impressive increase in yield has been observed for several hop cultivars grown with this technology, which encourages more growers to start hop cultivation. In regions where multiple growth cycles per year are possible, such as in the Palotina and Ribeirao Preto regions, the manipulation of flowering by using supplemental lighting may also be necessary to ensure high-yielding hops. In conclusion, the complete characterization of the climatic conditions of each location, especially the photoperiod throughout the year, is critical for successful hop production in subtropical climates.

Finally, beyond the hop photoperiod requirements, it has long been thought that hop plants require a low-temperature dormancy period, known as vernalization, in which the plant buds reset themselves under cold winter conditions to flower prolifically. By controlling the lighting periods with LEDs, which were not available a few years ago, it seems that the hops do not require the dormant vernalization period that was previously assumed to be essential for successful hop cultivation, as described by Bauerle [2], and depending on the climate conditions, multiple crops a year is possible. These new findings support the emerging initiatives of feasible hop production in subtropical areas where winter is mild and short and may encourage the expansion of hop growing areas in a wider latitude range around the world.

6. Perspectives of Hop Cultivation in the Future

The cultivation of well-adapted and high-yield cultivars in regions located in different latitudes in Brazil, in addition to promoting the development of new beer recipes with local typicity of bitterness and aroma for each region, may also create new business opportunities, since the plant can be also used in the pharmaceutical industry as a medicinal species. Almost all plant parts are rich in bioactive compounds such as bitter acids, and flavonoids, having potent antimicrobial, antioxidant, and antifungal activity, and these features, combined with the cultivation interest in natural-health-promoting substances, open new interesting perspectives for hops beyond the beer industry in the country. In addition, as reported by Rossini et al. [52], because only the female cones are of interest in the industrial cultivation of hops, a considerable quantity of plant residue is left in the field, and this leftover material is rich in bast fibers that can be used for paper and rope making and other bio-based materials, which can expand the hop cultivation as a novel multipurpose crop to a higher level in the upcoming years.