I spent the month of September 2011 back on the farm, getting it into shape and making batches of biochar. At the end of the month i took a truckload of the char down to Josiah’s biochar operation in Puna, where it was inoculated and ground up. Back at the farm, the living char was spread all over, especially in the tea field.
We live in a very rural, remote location – which is why it’s so surprising that Google actually got around to driving our neighborhood – but they did. You can even see the bottom part of our tea field clearly from the road, since the camera on the Google van is a bit higher than a person. Try the link: http://goo.gl/maps/khJt
Deb asked me one day to write something about how biochar fits into our farm. I scribbled a flowchart onto paper, and today put it into the computer; it looks like this:
Ideally, it’s a continuously flowing cycle; there is no “waste” and no need for unsustainable inputs; that’s the goal. The chickens provide meat and eggs to the humans, and poop to the compost cycle; the biochar stabilizes the nutrients in the urine and compost, making them plant-available longer. You can see how the compost pile is the engine in the middle of everything.
The full name of the document is “Specialty Crops for Pacific Island Agroforestry: Farm and Forestry Production and Marketing Profile for Tea (Camellia sinensis)”. It’s online at agroforestry.net (or directly to the PDF).
I contributed a bit to the document, with some reviewing, an illustration of using ginger as a mulch, and some notes on economics. I’m quite happy with the result, which in 32 pages manages to describe a great deal of what someone needs to know to grow tea in Hawai’i, and process and market it. There’s also some eye-opening statistics about tea in the rest of the world, where the cost of production can be 50x less.
A lot of this information is hard to come by unless you have one of the tea textbooks (the spotty Hajra book from India, or the wildly expensive Willson book from the UK), so it’s great that much of the important knowledge is now online for free.
Meanwhile, our tea continues to grow with astonishingly well. I am baffled by the textbooks which say tea should be “pruned back once every 3–4 years to a height that is comfortable for plucking.” Our tea only takes a few months to go from flat hedges to a wild, tall, profusion of growth. If this keeps up, it will need serious pruning twice a year just to keep it harvestable. Perhaps more frequent and aggressive plucking would help keep it under control, but there there are many other things on the farm (and building the new house) which distract from harvesting. One thing is for sure: the conditions here are very, very good for tea. The soil (just compost, biochar, & mulching) and wet Hamakua weather seem to be perfect.
Those of you following the biochar-hawaii list know that i’ve stopped using my kiln, and am now focused on making biochar in a pit. This is both for reasons of scalability and wear; my 55-gal steel drum kiln/retort could only make ~23-gal of char, and the surrounding kiln blocks cracked from repeated heating.
Hence, a pit. Mine is lined with blocks for clean char and easy unloading. Continuously fed wood, pyrolysis occurs at the air-starved bottom of the pile, gradually the pit fills up, then i cover and let it cool for a day, before opening and scooping out the finished char:
That first small pit worked well, so i made it bigger and sure enough, it scales well:
Width
Length
Depth
Gallons
Cubic feet
# of blocks
Gallons of Char
24
32
16
53.2
7.11
33
16.5
32
48
16
106.4
14.22
48
34
32
48
24
159.6
21.33
60
68
32
48
24
On second burn:
82
That 82-gallon operation took 2.5 hours to do the burn, then 2.25 hours the next day to unload, crush, sort, sift, and load into buckets. That’s 82/4.75 = 17.25 gallons of char per hour of work. That’s not bad, given that i’m working with some cheap concrete blocks, a piece of old corrugated roofing, and a shovel. With more money and technology, like a continuous pyrolysis machine, you could certainly get vastly more char per hour of labor, but those machines start at $100,000. I’m feeling quite happy about my pit. The Biochar2010 album has all the pictures.
I gave a biochar talk to the Kona Coffee Grower’s Association on June 2. 10 minutes of that talk got uploaded to YouTube. I then addressed the Hawaii Tropical Fruit Growers on July 19, that time with a fancy presentation with charts and pictures. Next will probably be an evening talk in Waimea on August 8, and then a 1-day workshop on making and using biochar here at our farm, date TBA.
Most of what i’ve been up to on the farm recently relates to biochar, but to keep this from becoming an all-biochar blog, here’s a bit about the garden.
I grew a patch of sunflowers this summer, planted mid-April. I needed to use row covers, to protect the seeds and sprouts from birds, until the plants are a few inches tall. It took 3 months for them to mature. At first i noticed that a lot of bees, and even butterflies, were interested in the flowers:
Soon after, i noticed cardinals feasting on the mature seeds, balancing on the tops of the head and pecking the seeds out, and shelling them right on the spot. That indicated they were ready for harvest, so i gathered a few for the chickens, then soon after, Deb harvested them all, dried them in the greenhouse and saved the biggest one for seed.
I recently did a second and third burn in my biochar kiln, tweaking each time. The story is best told in pictures:
Upon detailed inspection, the April test burn actually gave good results. Four white buckets are completely charred material, two orange buckets incomplete, one mixed and one of material from the surrounding fire.
Completely charred wood from retort, and the incompletely charred – only a small amount, and generally from the bottom of the barrel, perhaps due to a lower temperature there.
Preparing for burn #2, using smaller wood and some changes to the kiln.
Added a layer of firebrick at the base. Ideally, it should enclose the whole chamber, but that would take a lot of actual masonry.
More air inlets, allowing air into all four corners.
The ‘chimney’ is formed by the blocks themselves.
Smaller wood scraps for burn #2.
Opening the kiln after burn #2.
As before, the material at the bottom of the barrel (top, when inverted like this) is less charred, but everything above (below) it is completely charred
Much of the sticks that look brownish on the outside are actually completely charred black on the inside
Burn #3
Got the fire real hot this time, you can clearly hear the “whoosh” of the pyrolysis gasses from the barrel joining the fire
Sifting/crushing/sorting the result. Some 1/2″-minus has direct uses. The rest will soak in nutrients to charge it, then goes through the chipper-shredder to make “charged fines” – biochar fertilizer.
It’s been a long time since we’ve blogged about tea. The field has been growing exceedingly well, particular in the wet wet weather which stayed wet until mid-April this year. Tea loves rain! Our February 22 harvest, a full-bodied oolong, was announced on facebook and did well. The May 1 harvest experienced difficult conditions, surprisingly hot and dry, which sun-cooked the leaves even before processing. More recently, we did a harvest on May 21 which was made into two kinds of green tea: classic Chinese green, and my attempt at a Japanese green. The Chinese turned out very good. For the Japanese, we don’t have one of those heated tables that traditional rolling is done on, so i improvised. The result is promising – it does taste like sencha – but probably not yet good enough to sell. You can try some if you come by the farm.
Recent intern Alisha, picking leaves for the May 21 harvest made into green tea.
After the major pruning of 5/25, all the older plants are now hedges
Some young tea plants, freshly planted up the hillside. Recent intern Comus helped with much of the planting.
View of the lower field which is nearly all grown in, and now pruned into hedges
Note the pruning makes a lot of stick-ends, each of which should sprout multiple leaves next time, all at the same height for abundant and easy harvesting
As a followup to my last biochar post, i was sent the following document from Karl Frogner of UBI. Karl asked me to make it available, so i’ve put it here: Biochar Ovens, until UBI has a place for it on their own site.
It describes experiments conducted in Mongolia on making biochar in a steel drum where the combustion occurs in a metal center tube. Innovative and fascinating! I want to try it here on my farm, but i’ll have to somehow locate some heavy large-diameter metal pipe, and be able to make holes in it.
My friends Josiah and Jay down in Puna are producing biochar using a classic pit method, which seems to work well. I may end up making char that way as well, but there is some criticism on the biochar list of open burns, saying that emissions aren’t fully combusted and carbon yield is low, recommending a kiln or even better, a retort (closed “cooking vessel”). So, i looked at plans online and found two approaches, the two-drum and the Twin Oaks, particularly as built by Kelpie in Oregon. The first approach is too small a batch and requires multiple drum sizes, the second requires expensive metalwork including pipes and welding. I came up with a hybrid of the two approaches which should be cheap, simple and high yield.
I did my first trial fire-up yesterday. The trial results are from this picture onwards.
Results were promising, but need tuning. I learned a lot from this trial run. Some indications:
The kiln fire needs to be strong and hot and heat up fast. My kiln burned moderately, for a long time, so it didn’t fully cook the retort.
More air inputs. I was hoping to limit openings to focus the heat inside. I put vents on the left and right and front, but the fire seemed to want more air.
A round barrel in a square box isn’t great geometry for a fire, which tends to burn separately in the four corner “zones”. I could try stacking the blocks in a more circular arrangement, like a hexagon/octagon. If i stay with this arrangement, i’ll need air vents specifically pointing into each corner.
Chimney. I figured a simple rectangular hole at the back should suffice, since it worked for Kelpie. But mine didn’t seem to draw well. Charcoal kilns for a thousand years have had proper chimneys. I’ll probably need one too.
Insulation. I used regular CMUs because they’re cheap and available. No doubt better insulation would result from using firebrick, thereby focusing more heat inside. I could also fill/bury the hollow tile walls, even if they’re dry-stacked.
The half-charred results of this trial aren’t useless; they could still be used for a less-smoky cook fire, or dropped through my shredder to make mulch with a more stable carbon content. However, the goal remains easy, cheap, reliable full pyrolysis. If it doesn’t pan out with this design, i could always switch to a pit, or hybrid brick-lined pit, or other ideas.
As a followup to my last biochar post, i was sent the following document from Karl Frogner of 
