Obtaining Birch oil with dry distillation

In my last blog “Birch Uses and Dry Distillation” we looked at the properties of birch and some of the many uses the tree can provide for us. One of those key products was the birch oil obtained through dry distillation, and the tar gained through further rendering down of the volatiles to produce a tar, forming a thermosetting glue, a process that is thought to date back some 200,000 years and understood to be the oldest transformative process created by our ancestors.

In this week’s blog we will look at a step-by-step process of dry distillation and how this maybe achieved using modern materials found around the home, whilst documenting our results.

Things you will need include:

• First aid pack.
• Water.
• Heat resistant gloves.
• Shovel
• Birch bark.
• Metal biscuit tin, pre-burnt
• Food tin to collect the oil, pre-burnt
• Prepped safe area to have a fire or use of a fire pit
• Fuel for the fire.

Some optional items to help improve results could include:

• Bag of sand to seat the food tin in.
• Clay to seal the tins together.

In the UK we are not blessed with thick birch bark when compared to other countries further north in our hemisphere. Birch bark forms in many layers and in the UK the best I have managed to source is about 1mm in thickness in the south of the country (it may be slightly thicker further north) In Sweden I have come across birch bark up to 3mm thick! Increasing it’s usefulness and the amount of oil that can be harvested from it. To this end I tend to use bark that is less suitable for other craft uses like containers, when I want to extract birch oil through distillation.

The advice in the UK then is always to only harvest birch bark that a living tree is releasing and never to use a knife to remove all the layers of birch bark from a living tree as essentially it will die through those actions.

In other areas of the world where the bark is a lot thicker it is possible to harvest the layers of bark needed whilst leaving the tree enough to continue to grow. An example would be the first-generation Americans who selected specific trees of high quality that had been set aside for birch bark canoes. Once harvested and the tree left with enough layers of bark to continue to grow, however the bark would never return to the same quality which is why trees selected for canoe were so special.

In the above photo the fallen and rotting branch still provides birch bark suitable for dry distillation, if not for other crafts. The key indicator here is if the bark still has some flexibility to it, and so its worth taking the time to harvest. Anything that is brittle is best left being mindful this is still potentially habitat for invertebrates.

Remember to always seek permission when collecting your birch bark from the land owner and be mindful of any protected spaces like SSSi’s (Sites of Special Scientific Interest). Once you have collected your birch bark you will need to prepare it. Some bark, especially low-grade bark will often retain some of the cambium layer, especially if it is well rotted. Remove any of this to improve the results.

Place the dry bark it in a large metal tin, this can be in many small or one large coils, but ensure that they are no taler than the depth of the tin. The surfaces of the bark should run vertically for two reasons. Firstly, to prevent blocking of the holes in the bottom of the large tin, to allow the oil to flow out of and into the collection tin. Secondly to allow the oils to move down to the bottom of the large tin.

The tin must be prepared in a certain way to work. Firstly, select a tin (a biscuit tin is a good size) that has a good seal to the lid, as you do not want any of your oil escaping from here during the process. I dome out the bottom from the inside a little to help encourage the oil to travel to the centre, where I punch out a few holes no bigger than the collecting tin for obvious reasons. This can be drilled out or by hammering a large nail through from the inside. On both occasions I’ll Use a block of wood for support to give good results. Burn out your tins prior to using them for dry distilation to prevent any of the chemicals coating them contaminating your precious birch oil.

With the birch bark arranged in the prepared and burnt out metal tin it is time to turn our attention to preparing the fire site. This can either be done in a fire pit with sand or earth, or direct on the ground, ensuring the ground is prepared to prevent any environmental damage caused by the fire. Create a hole to receive the smaller food tin deep enough so that the top of the tin is level with the surface of the sand or soil.

For a matter of personal interest, I measured the weight of the birch bark to compare it with the yield that was extracted per 100g of birch bark. This was for a direct comparison with various more natural methods used (without metal tins) in a scientific report published in the Netherlands in 2017, which you can look forward to in my next blog.

Once the hole is made for the small food tin, I carefully extracted it to seal it to the birch bark tin with clay dug from the ground (modelling clay can also be used) to help prevent the oil escaping into the surrounding sand or earth, simply to maximise yield. It will still work without sealing it, just expect some loss of oil into the sand or earth.

Setting both tins (now connected by the sealing clay) into the fire pit we construct fuel around the larger tin. I have found two finger gauge fuel to work well. The burn needs to continue for about an hour or so. It is important to maintain this around all the tin to give an even burn, so ensure you have enough fuel for the duration. We are looking to achieve a fire anywhere between 250°C and above 500°C. bear in mind if the heat is too intense or the fire burns for too long, you will extract the volatiles and render it down to a thicker treacle like substance or a solid, creating a thermosetting glue rather than an oil.

After this time, we need to carefully remove the embers from around the large tin to prevent contaminating the oil once it is removed. Open the large tin carefully with gloves and check the contents. You are checking to ensure all the birch bark has burnt cleanly to maximise the oil you can harvest from it. If some bark remains unburnt replace the lid and put it back and rebuild the fire to continue the process. A successful burn will look like the image above and the contents will feel very light, Interestingly what is left is inert to any attempt to light it.

Upon revealing the oil your senses are immediately struck with the unique aroma of the oil containing betulene, betulenol, creosol, cresol, guaiacol, phenols and xylenol. It really is quite potent and probably best not to smell it, but I can never resist, it is the aroma of our ancestors and I feel a closer connection to them every time I produce this magic liquid.

So, What were the results. We packed 224.4g of bark into the large tin. Which resulted in 60.1g of oil equating to 26.74g per 100g of birch bark. This is nearly double what you would expect from the best natural methods which we will investigate next time. Have a go yourself and show us your own results in our facebook group

Jay