Lift a freshly cut piece of wood and it is heavy in the hand. Half of that weight, astonishingly, is water.
We think of wood as a hard solid, but a living tree is closer to a sponge swollen with water. Water drawn up from the roots soaks every corner of the trunk. So a freshly cut tree is half wood, half water.
You cannot burn water
This water is the problem.
For wood to burn it must first grow hot; but hold a flame to wet wood and the heat boils the water before it ever warms the wood. Just as a pot takes time to boil dry, the wood scarcely heats up until the water within it has all gone. And in the meantime the fire tires and dies.
Wood laden with water cannot make a good pellet. It will not catch, it burns only lukewarm, and you end up hauling heavy water across the sea for nothing. So making a pellet is, in half its labor, the work of driving out water.
But what do we dry it with?
Here a question arises. Drying wood takes heat — and where is that heat to come from?
Burning diesel or gas is simple, and many do just that. But to dry wood by burning fuel dug from underground is to send carbon dioxide out the back door while claiming to make a clean fuel at the front. It is spending behind what you earned ahead.
We dry wood with wood
So we take our heat from the wood itself.
In the last story we said that to reduce ash, the bark is stripped away. That stripped bark we do not throw out — we burn it, and with its heat we dry the wood. The bark that comes off on its own as the wood is trimmed turns out to be exactly the heat needed to dry that very wood. Not one drop of fossil fuel is newly drawn.
And the ash left from burning that bark returns, as we saw last time, to the soil. Not a single strip of the peeled bark is left with nowhere to go.
A freshly cut tree is half water by weight, so as it is, it barely catches and burns only lukewarm. Making a pellet is thus half the work of driving out water. The catch is that drying takes heat too — and if that heat comes from fossil fuel, the meaning of a clean pellet fades. So we burn the stripped bark to dry the wood: wood dried by what came from wood, and the ash left over returns to the soil.