December 28, 2011
As the size of our animal herds increase, we face several implications. One is the growing imperative to make good use of all of the animal when the time comes to harvest. While arguably this is a philosophical underpinning to our approach to animal husbandry, when we have just one or two
In the recent past, we have opted to use these products as nutrient dense compost. However, as the number of animals that are harvested seasonally increases, it behooves us to make highest and best use of these resources, particularly as we approach a point on the efficiency curve where the labor invested produces a notable amount of product. With time, we will be documenting more and more our approach to making use of these valuable, but often less popular, resources.
Here, I am going to talk briefly about our adventures in making bonemeal. The composition of bones could be described in two basic categories: organic and inorganic. The primary purpose of making bonemeal is to capture the inorganic constituents--primarily hydroxyapetite-- and use it as a soil amendment. Calcium and phosphorus, both contained in hydroxyapetite, are essential nutrients for plant growth. Phosphorus is required in relatively large quantities by plants, and is often a limiting factor in plant growth. Bones also contain, in smaller volumes, potassium, magnesium, manganese, boron, iron, zinc, sulphur, silica and selenium, all of which are also essential nutrients for plant growth.
The process we are developing for making bonemeal currently looks like this:
- During the butcher process we remove as much meat as possible from the bones.
- The bones are then boiled, with vinegar, to make a bone broth or stew (the vinegar helps to extract the calcium into the broth so that we can consume it directly). This process removes most of the flesh, connective tissue and bone marrow (the organic components of bones), however bone marrow is the most likely to still be present.
- The cooked and cleaned bones are then placed in the the solar dehydrator to thoroughly dry out. Making bone meal out of soaked through bones leads to sticky goupiness that clogs up the hammer mill.
- Once we have gathered a large enough collection of dry bones, then we grind them up using the hammer mill. Andrew has placed a screen over the bottom of the hammer mill so that bone particles need to be quite small before passing through the screen.
- We then gather up the bone materials and pass it through the hammer mill again, as there are always pieces that escape through the sides and are not as small as desired.
- Two passes through the hammer mill usually suffices. The bone meal is then scooped into a bucket and stored away for use as a soil amendment.
Dry Bones Collected in a Bucket
In using the hammer mill, we have found a few tricks make the work more effective and safer. The hammer mill has a tendency to fling whatever it is grinding everywhere--partially ground bone bits come flying back out the intake shoot and "finished product" is flung in 90 degrees on all sides of directly down. To collect the finished product, Andrew has built a large plywood box that the hammer mill rests in and catches most of the bone that exits out the bottom. We also use an additional piece of plywood to cover the shoot, to prevent bone bits from flying out the top and into our eyes. Also, bones need to be added to the hammer mill in relatively small increments. If too many are added at once, they get jammed and then all the bones have to be removed by hand before you can proceed. It's best to avoid this one all together.
Overall, this process works quite well. However it does rely on a gasoline powered engine. One option used by folks in the past to utilize the minerals in bones includes cooking the bones in fire, and then using the bone-char-ash mixture as a soil amendment. We have yet to experiment with this one, but it seems like a worthwhile endeavor.