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

Bones in the solar dehydrator
large animals (such as a sheep or a goat) to harvest in a season, and that To Do list is never quite finished, saving the organs for food, the fat for soaps and candles, the bones for bonemeal, the hides for leather, the intestinal lining for sausage casings and the skulls for crafts can become a task that involves a lot of labor without much total product.

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:

Hammer mill with the plywood box that collects the bonemeal

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.

Finished Bonemeal

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.