If you've had any success growing your own hops, you'll know (or soon learn) that properly drying them quickly becomes a complicated problem. A window screen works okay when you have a few ounces, but bigger harvest need special systems. This instructable will show you how to build a basic hop oast powered by a hair dryer. The basic design was adapter from the one found in The Homebrewers Garden.
The materials required to build a six bin oast are:
4' x 8' x 3/4" sheet of sanded plywood
2" x 4" x 8' stud
Enough screen or metal lathe for (6) 2' x 2' squares
A box of screws (1"-1.5")
A few longer galvanized nails
Step 1: Ripping the Plywood
From the plywood we're going to be getting (4) 8' planks 5 7/8" wide, (4) 4' planks 6 1/8" wide, a 24.5" x 24.5" square, and a smaller scrap piece we'll use later. There will be some loss of wood to the blade, but it's not a huge issue . We're not talking finish carpentry here. Getting some (or all) of the rips at the store can help if you don't have a good table saw.
After ripping the planks, cut them into 24" segments. Keep the set that came from each plank together so you don't need to worry about slight differences in the width between planks when framing the trays.
Step 2: Forming the Trays
Form six trays from each set of 24" planks by connecting them with butt joints as shown in the picture. Secure each corner with three screws. A corner jig helps. You'll wind up with (4) 5 7/8" tall trays and (2) 6 1/8" tall trays.
Step 3: Screening the Trays and Reinforcing the Corners
The lath comes in 27" wide sheets and needs to be cut down. It's tricky to precut because it has quite a bit of flex. I found it easiest to staple down two sides, cut the rest with an angle grinder, and finish stapling the rest. If you cut it with tin snips, wear gloves because the lath is SHARP. This is all a non issue if you are using screens. Crown staples and an air nailer work great for securing the lath/screen.
This thing doesn't need to withstand a hurricane but we want it reasonably sturdy. For the corners just rip a few strips about 3/4" wide from the scrap piece and chop them down to ~5." Use wood glue to secure them to the corners with some clamps to hold them while they dry.
Step 4: Adding the Tray Lips and Cutting the Base
For each tray you'll want to attach a lip to the top of each side. I made mine from a 1" x 4" I had lying around but if you're following my instructions you should have enough scrap left to make them from the plywood. That'd be the ideal route as the pine I used is really prone to splitting. Size is pretty flexible--I used 3.5" x 3" but as long as it rises about an inch or so above the top of the tray go nuts. Screw one down to each of the four trays sides.
The base is constructed similar to the trays but from the 2" x 4." Cut four lengths of 23 1/4" to get a final box size of 24 3/4" x 24 3/4." Drill a few good sized holes in each side of the base to allow moist air to exit from the bottom of the oast. Drill a hole in the middle of the lid wide enough for the nozzle of a hair dryer.
Step 5: Putting It All Together
Stack the trays on top of the base followed by the lid. You can run the oast one of two ways. The heat source can be placed on top, such as a hair dryer. The original plans recommended a bonnet style hair dryer set on low.
In practice it may make more sense to have the heat source underneath the oast. I have run it this way using the base of a dehydrator which heats and puts out a moderate air flow. When filled with more hops/bins, greater airflow will be required. The bins are the perfect size to fit a box fan. I plan to dry the bulk of my harvest by placing a box fan in the lowest tray.
Even better, if you have a temperature controller you can place the probe inside the oast and cycle the heater on/off to keep the ideal temp. Home growers have reported drying hops at 95-140 F. Commercially, they are usually dried 140-170 F but with a carefully regulated air speed. The trays closest to the heat source will dry faster so rotate them out as you dry. You can use just a couple trays or stack to your heart's content, so long as you have a powerful enough heater and fan to push the air.
Step 6: Oh the Hops!
The hops are dry enough once the central stem (strig) breaks more than bends. Oxygen is the enemy of hops, so it is important they are properly stored. For small amounts of hops, oxygen proof bags with the air squeezed out (or purged with nitrogen/CO2) work well. I prefer to pack my hops in vacuum sealed bags not only to get out oxygen, but to cut down on the storage size. Generally homegrown hops are recommended more for flavor/aroma additions due to the uncertainty in the actual alpha acid content. Growing hops is extremely rewarding. There's nothing quite like brewing a beer with the fruits of your labor. Good luck and happy growing/brewing.