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Kona Estate Coffee Dryer
10 April 2011


Ripe Coffee Pulping Frosty
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Our first harvest season on the farm, which seems like millennia ago, all we had was a rickety little pulper.  We sold most of our coffee to the local mill and only kept a few hundred pounds for ourselves.  With that little pulper, it would take us hours to process those few bags.  We'd sing Christmas carols as the whole family stood around the coffee pulper and helped.

Drying Drying consisted of laying the coffee beans out on several wire screens and raking them by hand.  Literally by hand since we didn't even have a coffee rake yet.  I'd visit other coffee farms and envy their giant pulpers and large drying decks.  I didn't realize how much work I had ahead of me.

I couldn't do anything without a barn so I started building one right away.  I designed the barn with a large coffee drying deck on top and room for a professional coffee pulper on one side.  It took several years to build it all.

The barn's drying deck is approximately 1500 square feet.  When I first designed the barn, I thought that would be plenty of space.  It turns out that it's not nearly enough.  It's fine when production is low but during the height of the season, the drying deck fills up quickly.  Last year I had to spend several thousand dollars to have someone else dry my overflow coffee for me.

Deck With even more production planned for this year, I need a better solution for drying coffee.  Sun drying is the traditional form of drying but it is totally impractical for larger amounts of coffee.  The coffee has to be raked constantly.  Even though the sun is free, when you figure in the cost of labor then sun drying is the most expensive way to dry coffee.

All the large mills use mechanical dryers.  The most popular style works like a giant clothes dryer.  The coffee is loaded into a giant rotating drum and hot air is pumped in to dry the coffee.  It usually takes one to two days per batch.  Drum dryers are simple and low on labor but extremely expensive to purchase.  The "small" model, which is slightly larger than what I need, costs about $20,000.  Add a few thousand more for the cost of propane, electricity and a building to keep it all in.

Many estate farms try building their own dryers.  A plywood box with a dehumidifier attached is a popular choice.  I've seen fancy versions and cheap versions.  I don't like any of them.  In my opinion, they're too small and labor intensive for what I need.

Drum dryer The barn's sun deck is great but I need a mechanical dryer too.  The professional dryers are all too expensive and the home-built dryers are all too small.  Being a do-it-yourself kind of guy, I decided I'd design and build my own dryer.  It's just a simple dryer, how hard could it possibly be?

My first few ideas seemed great until I started doing the math.  Starting with a given volume of freshly picked coffee cherry, I calculated the equivalent volume of both wet and dry parchment.  Then I calculated how much energy is required to dry that parchment.  It requires approximately 1.2 million BTU's to dry 50 bags of coffee cherry.  Giving myself two days per batch, and figuring in the efficiency of the heat source, means I need a 3-ton heat capacity.  That's about the same as a small house furnace.  Not too bad but far larger than I had initially thought.

That was just the start of the math.  I also had to figure airflow, both CFM and psi.  There's a lot of back pressure when forcing air through a thick layer of wet coffee.  I had to match all those numbers together to figure out how big and what shape to make the dryer.  I ended up spending several months working with a complex spreadsheet and CAD program.  I consulted with a professor from the University of Hawaii and read through several papers, including a master's thesis about a three-layer coffee dryer.  I have a folder on my computer with at least a dozen abandoned coffee dryer ideas.

It has taken far too long but I think I finally have a dryer design that will get the job done.  It's too small for the larger mills and too large for the average Kona coffee farm but just right for a mid-sized Kona coffee estate like Kona Earth.  I'm calling it the Kona Estate Dryer.  It will be energy efficient, highly automated, capable of drying a large variety of batch sizes and bean perfect.

Those last two parts are important.  Flexibility is important because during light rounds of harvesting I may only have a few bags of coffee each day but during heavy rounds of harvest, I can have a couple dozen bags or more.  I haven't seen any other coffee dryers that can handle such a large range of batch sizes.  Most processors simply lump smaller batches together but I want to keep them all separate for better quality control.

Parchment The bean perfect part refers to gentle and careful handling of the coffee.  With almost every dryer I looked at, especially the larger ones, a small percentage of coffee damage and loss is considered acceptable.  With thousands and thousands of pounds of coffee, what does a few beans matter?  Well, it only takes one bad bean to ruin a cup of coffee and someone will end up with those bad beans.  I want a dryer that does not create any bad beans.  I also want a dryer that doesn't spill beans all over the floor like some do.

Automation is another fun part of my dryer design.  Being an ex-computer programmer, I couldn't resist the urge to turn my coffee dryer into a giant robot.  It can run itself, loading and unloading coffee as necessary.  It will keep track of temperature, humidity, drying time and the amount of coffee processed.  I'll be able to download all that data into a spreadsheet.  I'll even be able to talk to the dryer with a laptop or cell phone.  The dryer will message me when it needs attention then I can check on its status and send new commands even if I'm at the beach.

Now that I have a design I'm happy with, the next step is to build the thing.  I figure it will cost about $10,000 which is expensive but about half price of a comparable dryer purchased and shipped to Kona from Colombia or Brazil.  I also have to build an extension onto my barn to house the dryer.  Luckily, I designed the barn for exactly such an extension.

Below is a drawing of my barn, its new extension and the fancy, shmancy Kona Estate Coffee Dryer.  If you see a picture of the dryer, click on it for more information.  If all you see is a box maked "classified", that's because you're not authorized.  I've put a lot of effort into designing this coffee dryer and I don't want to reveal the details until after I've built it.

I have put together a thick document with pictures, graphs, footnotes and all sorts of technical information on a variety of dryers.  If you're a coffee farmer, and you may be interesting in such a dryer for your own farm, then let me know and maybe I'll tell you more.  You can't have the CAD drawings or spreadsheet yet but I'll probably share my overview document.  I'm always happy to get any feedback I can.

For the rest of you, you'll just have to wait until the actual dryer is built.  I will need it in time for this next harvest which starts in August.  That's still a few months away but I have a lot of work to do before then.

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