Building trellis and planting rootstock requires a significant investment. Trellis is suspended over the yard by approximately 135 poles per hectare (55 poles per acre) and connected by high quality wire and cabling that stands five to six meters (16-19.5 ft.) above the ground. Traditionally, the U.S. hop industry has used a 7-ft. x 7-ft. (approximately 2 x 2 m.) spacing, which resulted in 1778 strings per acre. There were two work rows every 14-ft. (3.5 m.).
Growers typically cultivated a field in two directions with four tractor passes total, two in each direction. In the early 1980's growers began to change to a 3.5-ft. x 14-ft. (approximately 1 x 3 m.) spacing. Essentially, growers moved the middle row "out" to the pole row, in between the other plants. This resulted in one work row instead of two. By doing this, growers reduced their tractor work, and the associated expenses, by 75% because they only had to make one pass down the length of the field. Since the plants in the new layout were so close together, it was simply no longer possible to take the tractor across the rows. The number of strings per acre remained the same (1778 strings/acre).
As further encouragement to move toward wide spacing, traditional 7-ft. x 7-ft. spacing required the grower to "arch" the plants. "Arching" is simply the act of tying a string about waste high around the vines to keep them out of the way of the tractors. The labor involved with arching the vines cost about $15/acre ($37/hectare). Since the early 90's wide spacing has expanded rapidly together with drip irrigation. The most expensive part of establishing a drip irrigation yard is the tube. Since there are less work rows with wide spacing, it costs less to install the drip system. As of the year 2001, the majority of the industry has turned to wide spacing and drip irrigation is also becoming commonplace. In the quest for still greater efficiency, some growers are experimenting with alternative spacing techniques that would allow the number of passes through the field to remain the same while increasing the number of plants per acre.
Hops (humulus lupulus) are perennial plants whose rootstock will produce hops for many years. Some American hop varieties have still proven to be commercially viable after 50 years, but that is not the norm. In the never-ending quest for more efficient production and lower costs, the life of a commercial alpha hop variety has been drastically reduced. In the past, alpha hop varieties commonly produced for ten or more years before being replaced with quality rootstock of the same variety. Alpha hop varieties in the 21st century are removed and replaced with higher yielding varieties much more frequently than their predecessors. Aroma hop varieties however, are still replaced with quality rootstock approximately every ten years. These practices preserve optimum yields and enable the grower to be a more efficient producer.
Every spring, soil samples are taken from each hop yard to determine the soil fertility. Samples are analyzed and specific fertilization programs are developed for every hop yard to balance nutrients and assure the highest quality and the best yields. In late March, pruning with tractor drawn mechanical pruners prepares the hop plants for proper training time. Old dry vines and debris are often removed from yards although some growers practice no-till agriculture.
Also in the spring, twine is stretched from the overhead trellis network to the ground to provide support and direction for growing hop vines. During the month of May, one of the most labor-intensive parts of the hop growing process begins. Hop plants are trained to climb the twine supports. This entails field workers visiting each hop plant and wrapping several shoots around the twine support in a clockwise direction to begin their journey to the top of the trellis.
To control excess shoot growth, leaves and shoots are often striped from the main vine. By late May or early June, as determined by weather conditions, irrigation of the hop fields begins. Rill, sprinkler, and the increasingly popular drip irrigation methods are all used to provide the water demands of the hop plant. During an average growing season, the hop field will require 50-75 cm. (20-30 in.) of water.
Regular cultivation provides weed control, and improves soil texture. Cultivation takes place in each hop row, four to six times in each direction during a typical growing season. The season's first cultivation takes place in early April, after the soil has dried from winter precipitation. Final cultivation usually takes place in late June or early July, as the fibrous root system of the plant begins to grow. To protect the roots, no additional cultivation takes place until after harvest. Producing hops is a very labor-intensive enterprise, requiring a skilled labor force that has traditionally been available. Approximately one laborer for every six to eight hectares (15-20 acres) is required in the spring months. At harvest time, the number of laborers doubles.
Harvest begins by late August and can last just over a month depending upon the size of the farm and the varieties harvested. It is a very busy time when farm crews double in size and oftentimes work around the clock. Hop vines are first cut about one meter. (3-ft.) above the ground by an implement called a bottom cutter, which is attached to the front of a tractor.
Within minutes the vines are cut from the overhead support wires by a machine called a top cutter. The hop-laden vines fall into truck beds or trailers, which transport them to picking machines located nearby.
Typical picking machines can pick three to six hectares (7.5-15 acres) of hops per day, depending upon the variety and operating time. Hop vines enter the picking machine at the feeding station where vines enter upside down. Hops and leaves are stripped from the vines, which pass through the picking machine to the back of the system. Once there, they drop into a chopper and are turned into mulch, later to be returned to the soil. Leaves and hops fall through a traveling wire mesh and onto a conveyor which takes them through a series of cleaning devices that remove the leaves and stems from the hop cones.
Stems and leaves eventually are conveyed to trash, while the hops are cleaned and recleaned by a network of screens, drums, and dribble belts. Once the hops are nearly free of stems and leaves, they fall onto a conveyor for a trip to the kiln.
In the kilns, an automatic loader spreads clean hops across the kiln floor. A typical kiln floor is approximately 100 sq. m. (1056 square ft.), and will be evenly covered to a depth of a little less than one meter (approximately 1 yard). Traditionally hops rest on a floor that is covered by a loosely woven burlap cloth although some new kilns have metal floors with tiny holes through which hot air may pass. Oil and gas burners heat the air to a temperature of about 60¡-74¡Celsius (140¡-165¡ Fahrenheit). It is then forced through the bed of the freshly picked hops for about nine hours (Some varieties are more difficult to dry than others). During this time, the hop cone will lose up to 70% of its green weight and retain a moisture content of only 8-10%.
Once dried, cool, moist air is forced through the dried hops while still on the kiln floor. Conveyors then move the hops to a cooling room where they are allowed to continue cooling for 12-24 hours. During this cooling period, moisture spreads evenly throughout the hop cones.
After cooling, hops are conveyed to hydraulic balers that press the product into 200-pound (92-kilogram) bales. Bales measure 51x76x140 cm. (20x30x55 inches). Within 48 hours from the time the hops were harvested in the field, they are placed in cold storage warehouses.
Hops undergo comprehensive quality inspection. Bale lots, consisting of 200 to 400 bales, are sampled and inspected by the United States Department of Agriculture (USDA). Core samples from each lot are sent to the USDA certification laboratory where the samples are analyzed for leaf, stem and seed content. Each lot is then issued a certificate documenting its percentage of leaf, stem and seed content. The certification is necessary before growers may sell their hops. So precise is quality control, that individual identity of each lot of hops can be traced to its original grower.