BBOWT volunteers at Warburg Nature Reserve, nr Henley, have been continuing the traditional technique of making charcoal from wood, producing a sustainable product which is also of benefit to the woodland plants, insects and mammals.

Originally charcoal was produced in earth piles or “clamps” covered with turf but a metal kiln with air inlets and chimneys is now used. The kiln is stacked with air dried hard wood, which has been coppiced from the reserve as part of the woodland management work programme.

Coppicing is a traditional form of woodland management that has shaped many of the remaining woodlands in the UK. It is the technique of repeatedly felling trees at the base, which stimulates regrowth and actually prolongs the life of the tree.

Cutting down the trees in patches or “coupes” opens up woodlands and increases woodland biodiversity, as greater amounts of light can reach the ground, allowing other species to grow. Many of these species are food sources for butterflies and other insects, which in turn provide food for birds, bats and mammals. 

So back to the fire! Coppicing in Warburg is carried out between November and March, and the wood stored and air dried for the following season.

The burn all starts with “stringers” laid out on the kiln bottom like the spokes of a wheel, which helps to create an even flow of air allowing the fire to spread.

All the dry wood that has been sawn to size is now stacked into the kiln around a central former. After making sure that all the air inlets are clear the wooden former is removed and burning charcoal introduced down the central column to ignite the wood.

When the wood has caught light really well the lid is gently lowered onto the kiln, the air intakes sealed and the chimneys inserted with everything being sealed with earth, ready for the pyrolysis magic to begin.

Charcoal making involves burning the wood slowly at a very high temperature, around 400-470^oC, with very little oxygen. It is a fine balance. The length of the burn varies but roughly takes about 24-36 hours.

A slow burn is vital for the production of good quality charcoal so the change in the colour of the smoke produced is used as an indicator of the state of the burn. Once lit the smoke appears white as the water vapour is burnt off, turning to yellow as the tar is burnt and eventually a thin blue, as the wood starts to convert to charcoal.

At Warburg the kiln is left for two weeks to cool down before it is opened up ready to be processed. One lucky volunteer gets to go into the kiln to empty out the lump charcoal which is graded through rotating sieves. Any unburned or “brown bits” are set aside for the next burn together with the smaller pieces so that only the premium charcoal is weighed into the bags to be sold to raise funds for BBOWT. Although hard work and really messy, it’s great fun being part of the Charcoal Team!

So, the next time you are going to buy your charcoal for the barbecue think about the benefits of buying from your local woodland supplier:

• A sustainable resource, because the carbon released on burning is balanced by the carbon intake of the re-growing trees.
• Buying locally-produced charcoal reduces the transport carbon footprint.
• You are helping the woodlands though coppicing and promoting biodiversity.