Once plucked from the bine, the brew kettle is the ultimate destination for the vast majority of hop cones. What happens to the hops along the way depends on whose brew kettle they are headed for. Brewers use hops in various forms. Some brewers like to make a seasonal beer with freshly picked wet hops—also called fresh hops or green hops—that have not been dried or processed in any way. But all the other forms—dry hops, hop pellets, or hop extracts—require drying the cones first to preserve them. If fresh-picked hops are not used or dried immediately after harvest, they will quickly rot, and the lupulin, along with the alpha and beta acids, will be destroyed.
For as long as people have been growing hops, they have been processing them by drying them. Whether that drying takes place in massive industrial kilns, on ad hoc drying tables made from propped-up screen doors in a living room filled with fans, or in one of the historical oast houses still dotting the rural landscape, it is an urgent and delicate process. The quality of the hops you worked hard to grow hangs in the balance: dry them too fast, at too hot a temperature or not enough—and all is lost.
Brewer Sam Richardson presides over the brew kettle at Other Half Brewing Company in Brooklyn, New York.
Once hops are dried, they become relatively shelf stable—though eventually the alpha and beta acids and hop oils contained in dried hops will begin to degrade in quality. Improper drying or storage can accelerate that process, but over the years technology has brought new advances.
When you dry hops you are essentially removing most of the moisture from the hop cone. During the process 1 pound (0.5 kilogram) of destined-to-be dry hops must shed 3 pounds (1.4 kilograms) of water, the equivalent of a little bit less than 1/2 gallon (1.9 liters). Removing the moisture slows the decomposition process of the plant matter and preserves the important alpha and beta acids and hop oil contained in the lupulin. Creating the optimal conditions for drying hops involves an exacting balance of heat and air circulation over a carefully managed period of time. On a commercial hop farm, the low, meditative hum of the drying kiln manned by one or two people is a stark contrast to the bustling human activity surrounding the roar and clatter of the harvesting machine.
How the Large Commercial Growers Do It
On a large commercial hop farm, the harvest is somewhat like a relentless assembly line that runs twenty-four hours a day. If all goes according to plan, hop cones will be dried and baled between twenty-four and thirty-six hours from the time the bine they were growing on was cut. The pace is driven by the necessity of preserving the lupulin contained within the hop cones before it starts to degrade. Remember, the higher the level of acids and essential oil in the hop, the higher the price. Field workers move machinery up and down the rows of the hop yard, cutting bines and trucking them to the harvesting machine, where the cones are removed. The harvested cones flow steadily into the drying kilns.
Harvested hops spilling onto the kiln floor.
When the cones arrive at the drying kiln they have a moisture content of 76 to 80 percent. In the kilns they are dried to a moisture level between 8 and 10 percent. The harvest can progress only as fast as the hops can be dried. If drying space is limited, which it often is because kilns are extremely expensive to install, the kilning process can be a bottleneck, slowing the harvest. The quality of mature hop cones awaiting harvest will begin to degrade on the bine. The solution to this capacity problem has been to speed up the drying process by increasing the temperature. But that approach can backfire because a higher temperature can degrade the quality of the acids and oils, reducing the value of the hops.
In a commodity market where hops are being purchased cheaply for mass-produced beer, this is not as much of an issue. But lately, as craft brewers become more and more particular about the quality of their hops, growers are lowering the temperatures in their kilns and instead increasing the volume of air circulating or simply giving the hops more time to dry. Historically, hops have been dried at a temperature of about 160 degrees Fahrenheit (71.1 degrees Celsius) over a period of approximately six hours. Today the trend is to dry the cones at lower temperatures over a longer period of time. When we visited Crosby Hop Farm, they were drying their hops at a temperature of 128 degrees Fahrenheit (53.3 degrees Celsius) over an eight-hour period.
In the 1800s, hops were dried on the second floor of barns called hop houses or hop kilns, with rising heat generated by woodstoves located below the drying floor on the first story. This basic concept has remained unchanged. Today a hop-drying kiln on a commercial hop farm is often still a two-story building. Propane boilers located on the lower level blast heat upward through the floor of the second story where the hops lie. The hops are fed onto the floor by the conveyor belt running from the building housing the hop-harvesting machine. The floor is covered with a layer of burlap and divided into sections by short walls about 3 feet (0.9 meter) high. A section will be filled to a depth of about 2 feet (0.6 meter). The flow of hops onto the drying floor is monitored by one employee while another closely tracks the temperature and moisture levels. As the heat and air circulate through the hops, they release their moisture. Leaning over the kilning floor you can feel and smell the warm bitter heat rising against your face. Moisture levels are tested by employees wielding probes who walk out onto the hops wearing large flat boards strapped to their feet, referred to as hop snowshoes, so as not to crush the cones.
Once the hops are sufficiently dry, the burlap underneath them is rolled up—feeding the hops on to another conveyor belt which takes them into the conditioning room. The conditioning room is essentially a big empty warehouse divided into sections. The hop cones are dropped onto the floor in an enormous pile and left to sit for about twenty-four hours. Conditioning is necessary because in the hop kiln the hops on the bottom, closer to the heat source, become drier than the hops on top. While the hops are in the conditioning room, the moisture levels equalize as the temperature drops. This process is also called cooling or curing. Once they are done conditioning, the hops are baled.
A pair of plywood hop snowshoes lies ready at Goschie Farms. A worker monitoring the drying process will don the snowshoes to walk along the surface of the hops to the center of the kilns to test the moisture level.
Hops heaped high on the conditioning room floor where the temperature and moisture levels are allowed to equalize over a period of about twenty-four hours.
Drying Options for Home Growers
Obviously a hobby hop grower is not going to need all this big expensive equipment, but the basic principles remain the same. After your hops are picked off the bine they are very moist. If they are not used immediately in a wet-hopped brew, they will begin to rot. How you dry them really depends on how many hops you have.
Air drying can work well, providing you have enough space. One method of air drying is to spread the hops out on a horizontal screen. Make sure the screen is clean and dry before you put the hops on it. Elevate the screen like a tabletop. That way you are getting air on the hops from both above and below. Enhance air circulation by setting up fans around the screen. Make sure the hops are out of the sun, as sun drying will compromise their quality. How long it will take to dry hops using this method will really depend on the weather. In warm, dry weather it could only take a couple of days. In wet, humid weather it could take a week. Check them several times a day, and stir and turn them a bit.
In their early days of cultivation, hops were generally dried in the open air, but when commercial hop production ramped up, economic viability demanded the drying process speed up. Given the resources available at the time, the best way to achieve this was by applying heat—and large kilns called oast houses began popping up in England and other beer-brewing regions of Europe as early as the sixteenth century. An early oast house was essentially a one-story building with curved walls and a wood-fired brick furnace located on the ground. A wooden slat floor was installed a few feet above the furnace, with about 1/4 inch (0.6 centimeters) of space in between each slat. The hops were spread on this floor. Heat rose up through the slatted floor from the furnace below, and the heat and moisture were vented through a roof shaped like an upside down ice cream cone.
Oast houses based on this design were built in the English colonies, too, and over time innovations were made. In the 1800s a typical oast house, by then called a hop kiln, was a vertical two-story building, usually built from stone into a bank or hill with a pyramid-shaped roof. A coal-fired furnace on the bottom floor generated the heat, which rose up through the slatted floor and vented through the roof. The drying process was also referred to at this time as “curing.” As hop production increased, the hop kilns were added onto, creating four or even more bays, each with its own furnace. In many cases the dried hops were stored in the same building that housed the kiln. As you can imagine, fires were not unheard of and proved disastrous when not only the kiln but also the entire processed and stored crop was lost.
Regulating temperature was tough under these conditions, and hops were often overdried, in some cases turning brown during the process. Sulfur was burned in the kiln to green the hops up again after drying but even though the color changed, the damage was done. Many diatribes were written in newspapers and hop industry publications about the problem of ruining hops with high heat. In 1883 Ezra Meeker, author of Hop Culture in the United States, wrote, “Almost any inexperienced farmer can raise hops, but nothing short of the most vigilant, careful and intelligent management will prepare the crop, without injury, ready for market; hence the curing is the all important part of hop growing and if not properly done, results in great loss and final failure.”
An old-style hop kiln from the 1800s still stands in Clarksville, New York.
In this picture from our early days growing hops for home use, we are drying hops on a screen. The chicken wire that can be seen lying over the top of the hops has nothing to do with the drying process but is instead being used to deter a curious barn cat.
Clever people have come up with a lot of different ways to dry hops at home and shared them online, ranging from outfitting a cabinet with a hair dryer to sandwiching hops between furnace filters and strapping them to a box fan with a bungee cord. But more familiar kitchen methods work, too. A food dehydrator can be used to dry hops, with the major limiting factor being its low capacity. This method works well for home brewers who are harvesting a pound or so of wet hops a day and want to put them in the dehydrator overnight. Be careful to set the dehydrator between 120 and 140 degrees Fahrenheit (48.9 and 60 degrees Celsius), and dry the hops overnight. Hops can also be dried in the oven on the warm setting providing it does not reach over 140 degrees Fahrenheit. Set your oven on warm, and let it run for a while, then put a thermometer in it to see what the temperature is before putting in your hops. Small amounts of hops can be dried in the microwave in a matter of minutes, but this is not recommended because the temperature will get too high and damage the hops.
Drying Options for Small-Scale Commercial Growers
Although some manufacturers have begun to produce hop-harvesting machinery for small-scale commercial hop farms, there is currently a real missing link in between the box fan and screen method and the technologically advanced hop kilns in the Northwest. Small-scale growers have the option of building their own oast houses. If you have an engineering bent you can devise your own system—or you can download plans online.
The modular oast house designed by UVM has numerous drawers, enabling multiple varieties of hops to be dried at the same time without mixing. Plans are available online.
This drying kiln built by Steenland Manufacturing uses only air circulation to dry the hops and works very well.
UVM has designed and made plans available for a modular oast house that is essentially a heated cabinet outfitted with screened trays in the form of drawers and fans (see Resources). The system of drawers is a great way to keep hop varieties separate during drying. It is 4 feet (1.2 meters) wide, 4 feet deep, and 8 feet (2.4 meters) tall and made with readily available materials. This unit can bring 300 pounds (136.1 kilograms) of wet hops down to a moisture level of 10 percent in eight hours.
In the past we have relied on a drying machine from Steenland to dry all of our hops. Its limited capacity slowed down our harvest to a degree, but it worked out. Prior to that we relied exclusively on the box fan and screen method, except in the case of the collapsed trellis, in which the hops dried on the living room floor. Now that we have grown, we are purchasing a hop dryer manufactured by Wolf (for $4,800) with multiple layers and enough drying capacity to process up to 30 acres (12.1 hectares) of hops. Although we will not need all of this drying capacity for our own hops, we plan to offer drying services to other growers in our region since so many are suffering from a lack of infrastructure. One advantage of getting started growing hops is that they take several years to mature and reach full production. Your first harvests will be small, giving you time to experiment and ramp up to the purchase of infrastructure that will allow you to process your crop once the hop yard comes into full production.
How to Tell When Hops Are Dry
When hops are first picked, their moisture level should be between 76 and 80 percent of their weight. Hops are considered dry when the moisture level has been reduced to between 8 and 10 percent of their weight. When the hops are dry they will feel dry even when you squeeze them. When the cone is dry the stems should snap, not bend under pressure. To make a scientific calculation, use the same formula that you used to decide when to harvest.
Large farms use moisture probes to test moisture levels. The problem is these are larger than what small-scale growers need and are prohibitively expensive. When we visited Goschie Farms, they were using a moisture meter called the Moist-VU DL6000 made by Reid Instruments. It costs over $7,000. That prompted us to call Tom Reid of Reid Instruments and see if there were options for a farm our size. It turned out that he had been getting a lot of demand from marijuana growers for a smaller moisture meter, so he had been working on developing a tabletop version called the DL4000 that he thinks would work for small-scale hop growers as well. He estimates it will cost about $4,500. That seems like a lot of money, but when you consider that the success of the whole crop depends on the accuracy of the moisture reading, it is worth it.
Since our initial phone call with Tom Reid, Reid Instruments is selling the Moist-Vu DL4000 (see Resources). It measures the moisture level of a bagged sample of loose cones placed on a sensor plate using the same ultrasonic measuring device as the moisture probe. Reid Instruments is providing us with a model for trial use this fall.
There is a lot at stake in getting the dryness/moisture ratio right. If you dry your cones to a lower moisture percentage, they will begin to fall apart and the lupulin inside will disintegrate and be lost. If the hops are too moist, you run the risk of their oxidizing, turning brown and moldy, or even heating up and starting a fire through spontaneous combustion—like hay that is still wet when baled. Normally all hop bales going into storage are tested with a moisture probe designed for bales to make sure they have been properly dried. But 4 percent of the nation’s total hop crop in October of 2006 was lost as 2 million pounds (907,000 kilograms) of hops burned in a Yakima warehouse fire resulting from the spontaneous combustion of hops not fully dried. “Yeah, that was us,” said a sheepish Paul Matthews, of Hopsteiner, who told us the story.
The moisture probe used on Goschie Farms, the Moist-VU DL6000 made by Reid Instruments, is used to determine the moisture level of a layer of hops lying 2 feet (0.6 meter) deep on the kiln floor.
