Sunday, October 20, 2013

Biochar from Butchering Waste

One thing that's been on our minds lately as our chickens rapidly approach the age at which they are released into our small, electrically-cooled pasture is, 'what do we do with the butchering leftovers?'  Growing up, anything leftover from meat-processing or meat-eating operations went out into the open field or out in the woods, just far enough away that the dog wouldn't find it and regurgitate it in the living room.  Sometimes the dog did find it anyway, and if that happened, Dad decreed for the next several batches of meat-related waste that it needed to be taken twice as far and buried at least ten feet deep.  Our impression is that this approach is followed by many other folks, as well, with many variations on the theme.  Cheap and easy?  Definitely.  Sanitary or good for keeping coyotes and raccoons away from your chickens?  Not so much.

On the other hand, if livestock are taken to the local meat market for processing, the guts and feathers and other stuff that doesn't make it to the plate are often hauled away at cost to the butcher, to be rendered into soap, glue, and food for future generations of livestock.  Although that's been changing (especially abroad) thanks to Bovine Spongiform Encephalopathy (BSE, or mad cow disease), dealing with slaughterhouse waste is still a big problem.

Cornell University has a good article discussing different options for taking care of this waste responsibly.  Both economically and ecologically, composting emerges victorious, but there are several considerations that must be taken into account for a favorable outcome.  The first is to have a site available that is well-drained and 200 feet away from any surface water source.  The second is to have lots and lots of high-carbon organic matter (such as wood chips or sawdust) available.  The third is to not have any neighbors that object to the smell if you plan to turn the compost pile in the first 3-6 months.  We're 0 for 3 on that checklist.

In the past, we've had some success with using worm composting to decompose meat-processing waste.  But, like standard composting, precautions must be taken to eliminate odor, including the use of a lot of bedding above the waste.  Also, there's no way our current worm bin size could handle the leftovers from processing seventeen chickens, and we don't know how the vermi's would do with feathers.

Then, earlier this spring, an interesting article, Biochar of Animal Origin, came out in the academic literature about processing butchering waste into biochar for use as a soil amendment.  In particular, the authors focus on the use of animal-bone biochar as a replacement for phosphate rock fertilizers (which are the current phosphate source for most of the industrial agriculture system).  The article is set in the context of averting peak phosphorus (phosphate rock is a rapidly-depleting non-renewable resource), mitigating fertilizer runoff from large-scale fertilizer misapplication, and reducing an industrial waste product (animal bones).  None of those problems may seem particularly pertinent to homesteading-minded folks, but many homesteaders both generate animal-processing waste and make biochar from wood as a soil amendment.  It seems that converting meat-related wastes into a useful product like bio-char would be a permaculture-consistent, hygienic way to process them, even if one did have the space to drag the bones, gristle, and feathers half a mile and bury it ten feet deep like Dad said.

Why would one want to make biochar, other than to get rid of a waste product?  There are a lot of good resources out there on the internets explaining the benefits, but we recommend checking out Anna's lunchtime series on biochar over at the Walden Effect and Shaun's discussion of the matter over at Shaun's Backyard as a good starting point.  Briefly, biochar improves soil nutrient-holding capability (via ion exchange capacity) and texture, and has a porous structure that houses beneficial bacteria.  The bacteria in turn further increase nutrient availability to plants, in part by producing metabolic products that break down the biochar itself (but the carbon base pretty much stays put).  For example, the sciencey paper linked above discusses inoculating biochar with bacteria that produce acidic metabolites, which make the phosphorus in the biochar soluble (and thus available to plants).

Here's a scheme of how animal biochar could fit into a homestead's operation.  Here's a riddle: what becomes naked as it gets dressed?  A chicken!

We haven't tried making biochar yet, but we're working on a biochar retort/oven that we'll hopefully be able to report on in a few weeks.  In the meantime, how do you dispose of your meat-related wastes?  Have you made biochar on a small scale?  Have you made biochar from anything meat-related?  (Other than accidentally burning steaks on the grill.  That doesn't count unless you used then used the char for something useful.)  Let us know in the comments section below!


  1. We've tried putting the entrails and feathers in the composting toilet, which would have worked except we hadn't blocked it off well enough to prevent our dog from getting in. Smell didn't seem to be an issue since I covered it well with sawdust.

    But since the first try in the composting toilet wasn't a success, now we generally pick a lawn spot between fruit trees, where the ground needs to be enriched for later tree roots, and bury everything about two feet deep. A cinderblock on top for a few days is enough to deter our dog, and pretty soon our soil life has rotted everything away. Bones are supposed to be great for fruit trees, so I figure we're not really wasting the "waste." Plus, simple is good at the end of a long day of slaughter....

    1. I agree with you on the value of simplicity at the end of a long day, and that strategic burying is definitely not wasting it. If you've got a spot to bury it that won't contaminate your water, I say go for it!

      I would guess that folks who pay attention to the health of their soil (like you!) have dirt with a ton of organic matter and armies of microbes ready to go, so burying it is probably not that far off of what the article from Cornell recommends anyway. :-)

  2. I put meat scraps, feathers, small bones, and unused entrails in a bokashi composting bin. Larger bones are first used for soup stock then burned for bone ash used as fertilizer.