Pallet Hop Dryer Introduction After reviewing some great work that the University of Vermont did to create a multi shelf hop oast (http://farmhack.org/tools/modular-hop-oast-or-tray-drier-herbs), I decided to take on a challenge to try and create a prototype dryer for much less money. The UVM dryer cost was close to $1000, my goal was to create one for ~$100. The multi-shelf UVM approach is great because it allows different hop types to be dried at the same time. I was shooting for a good days picking or around 60 lbs of wet hops to dry per day. I kept that same approach and used pallets and other lower cost items to keep the raw material costs low. The results show that overall it can be done and the following documents how I put it together (with help from friends) and proved it out. Design and Build The UVM hops dryer basically had an overall framework with heater, controller, and circulation fan, hop shelves, and ports for air entry and humidified air exit. Using that overall concept I started to gather materials needed to get it going. First I started to gather pallets as I decided that spending money for ¾ plywood would put me way over budget. Businesses toss out pallets by the road all over and its good wood. The overall idea was to use fans in the bottom of a box made out of pallets to move air through shelves made from pallets, provide a heat source to accelerate the process and control the temperature, then provide an exit port for humidity to get out. I also wanted thermal mass so when it got to temperature, it would hold better, so extra wood was ok. I picked up a couple of inexpensive box fans from Walmart for air circulation that is also shown in the picture. I figured these would fit nicely on pallets. I started to take apart pallets to gather wood for making boxes and overall framework. A saws all is a great tool! No two pallets are alike so it was tricky putting it all together.
I then realized that I didn t have a enough pallets and the ones I had were not in great shape. My daughter and son in law found more a couple days into the project and delivered them to me which worked out great. My friend Tom had some leftover ¾ plywood strips from a job he wanted to get rid of so I took them for potential use. I started to rough out the hot box for the hops. I built the box on a level part of my garage floor starting with a sturdy pallet base. I tried to match up pallets based on size and quality to form the sides, back, and top. I placed ¾ plywood on the bottom, top and back walls as that is all I had from Tom. I used nice quality pallet boards and screwed them into the insides of the box to help close things up. Note: The intent of the box was not to seal it up, but to allow air leakage and expansion under humidity conditions. You can see the air gaps in the pictures. Note: All screws holes were countersunk drilled 1 st Once I had the box framework completed I went to work on a door. This was tricky because it had to close fairly tight to the front of the box so I found a very good pallet and cut narrow strips to fill in the gaps in the pallet, but flush to the face. I then installed the door using some home depot utility hinges and also did a fan fit check. Overall the box exterior dimensions not including the casters are 44 wide x 48 deep x 40 high.
Next I installed supports on the side walls for the hop trays. I then cut a 6 hole in the side of the box that was located directly in between where the center of the fans would end up. This was my heater input with the flexible duct to help line it up. I then built some hop trays, 24 wide x 37 long x ~4 deep depending on boards available from pallets or ¾ wood.
I installed 4 swivel casters (2 locking, 2 free) from underneath on the overall hot box (the box was really heavy so jacks were used), some outriggers on the hop trays, and installed for a fit check. I also built some standoff for the fans shown in the bottom and some air filter holders. The back face had a hole drilled to run the fan cords through (it s important to keep the cords away from the incoming heat source). I then put the fans in, drilled a hole in the top right corner near the door for the Inkbird temperature probe and a 1.25 exit port in the top right of the box opposite the heater and hooked everything up. Ran the fans to a separate outlet as the heater draws 13 amps and I didn t want an issue. The box heated up to temp a target temp of 108F in about 30 minutes with the fans on high (2500 CFM each). I let it cycle between 108F and 106F for about an hour and it held steady with the heater kicking on about every couple minutes. Woohoo!
I then took the boxes and fans out and used some leftover Behr wood cleaner and sprayed the entire hot box and hop trays, then did a thorough washing. I let them dry in the sun then used some leftover Tried and True Linseed oil to food safe the hop trays and also the hot box interior. It was then onto a trailer and off to my friend Andy s Hopsagon for a trial run with CTZ hops.
Trial Run The trial run was 6.5 lbs of wet CTZ that we wanted to put in the pallet hop dryer for a whirl. We ran a cycle from 73F (air temp) to 108F for 5 hours starting at 10AM, then cut off the heat and we let the fans run. The 1 st and 2 nd bins from the bottom had CTZ, the 3 rd bin up had a very small amount of the Horizon variety. After about an hour the internal probe temperature was 100F. At 8pm the hops were checked and the bottom bin of hops were nicely dried, the 2 nd bin up needed a little more time so those two bins were switched. The fans were left on and heat off, the next morning the internal box temp was 88F and all hops were perfect. 6.5 lbs of CTZ is now 2.5 lbs, then vacuum sealed and frozen. All in all a fun project that took a couple weeks to build, we learned a lot and are already looking at tinkering with improvements. We think: a) through the drying cycle we will have to rotate the boxes as the bottom one will get the most juice. b) the fans are starved for air so we are going to raise them up an inch and possibly angle them. c) that we will need to add another humid air exit port top dead center in the box. d) the hop box support mesh that wasn t shown will need more support in the boxes. e) that we will need to add a ductwork shield to direct the heat to under the fans. Really looking forward to next season when we can load up the dryer and fully exercise it!
Bill of Materials Pallets (free) Plastic mesh for boxes (free from my friend Andy (not shown) Tried and True Linseed Oil and Behr wood cleaner (free leftover) Tractor Supply RedStone Ceramic Barrel Utility Heater, CZ285RDTS ($34.99) Walmart Lasko 20" Box 3-Speed Fan, Model #B20200, White (2) $16.88 ea = $33.76 Amazon Inkbird C206T 1500W Heat Mat Temperature Controller, Day and Night Thermostat, 6.56FT NTC Sensor, F and C Degree, -58-212 F = $29.99 Amazon Coocheer 4 Swivel Caster Wheels With Top Plate & Bearing Heavy Duty On Red Polyurethane Wheels Set of 4 (2 Swivel Without Brake, 2 Swivel with Brakes) = $29.99 Misc Items from Home Depot: Utility Door Hinges $7 20 x 20 Furnace Filters $5 6 Adjustable Ductwork $5 Outdoor Screws $8 Total Cost = ~$165 with tax