Mesolithic Kicks – Birch Tar

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If you pursue the art of foraging for any amount of time, sooner or later you begin to unearth some of the lost techniques that people used (and still use) to process, prepare and preserve wild food. Inherently linked with these techniques are those used to produce all the non-edible daily things we prefer not to do without.

A few things become apparent when experimenting with any long-tried ‘lost’ technique: firstly, that the means of making or obtaining even the most fundamental of household ‘things’ (for example yeast, lye, charcoal, vinegar, etc.) are beyond the common abilities of most of us, though with a bit of research, we could probably produce them. That said, for the longest part of human history the production of our day-to-day consumables required a level of skill and intimate practical knowledge far more developed than those obtained since man began to work the land.

Secondly, in a pre ‘cottage industry’ set-up, the effort people were prepared to put in to produce something reflected how indispensable that thing was. Picking, drying, crushing, threshing, winnowing, cleaning, roasting, and other such techniques were often carried out not because of absolute necessity, but because once discovered the finished product could not ‘comfortably’ be done without.

Thirdly, that the people responsible for coming across and developing these techniques must have been some of the most creative, curious, patient, persistent, and above all ‘normal’ people who ever lived, and stumbling upon, or finally managing to perfect a certain new technique, they must have experienced a kind of elation and joy and sense of mastery of their world that we can perhaps only dream of. Unless we attempt to recreate it from Thursday to Friday afternoon.

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A good friend of mine went to a ‘museum village’ near Berlin where traditional skills are still practised and the products sold to visitors. He brought me back a small jar of birch tar.

Put simply, birch tar is a thermoplastic (re-malleable) material extracted from birch bark using heat. At its simplest it can be used as an adhesive, and as it can be remoulded after solidifying, it is almost completely reusable. In the middle stone age it was used for fixing arrowheads and fletchings onto arrow-shafts (see www.continuas.org/texts/benozzo_distillation.pdf). Later it was used to caulk boats (see http://anthropology.tamu.edu/papers/Franklin-MA1985.pdf), and for waterproofing, sealing, and gluing, and due to its betulin content it has been used as a kind of ointment for the treatment of skin diseases, though little information is available as to exactly how or by whom it was used in this way. The jolly curators of the museum village in Düppel, where my friend found me the sample birch tar, seem to rate its medicinal value quite highly; the label reads as follows: Wenn Pech, Schnapps, und Sauna nicht helfen, führt die Krankheit zum Tode (“If birch tar, schnapps, and sauna do not help, then the illness is fatal.”)

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As has already been said, birch tar is created by heating the bark, importantly in an airtight vessel, comprising of a drum for the bark and a smaller and a smaller vessel underneath it to collect the tar itself. Researching the methodology, we (or better to say my friend) came across various techniques, and ours ended up a combination between elements of different methods, with a bit of common sense and a willingness to learn from having things go wrong the first time.

As said, our method was the double-pot method. The bark container on top can be made out of anything that will withstand a roaring fire. We opted for a pail which we stuffed with birch bark and turned upside down to fit onto an old paella pan, mainly because those were the materials we had to hand. We packed a full travel rucksack’s worth of bark into our container.

The bottom of your bark container will need to be pierced to allow the birch tar to collect in the lower container. Do this while holding the sides so that surface becomes slightly concave; this will hopefully help the run-off of the tar. We also pressed a chicken-wire insert into the bucket to keep the bark in place as to stop pieces of charred bark blocking the hole, but this might not even be necessary.

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Your tar collector can be at least one-third smaller than your bark container, and should be buried in the ground to just above the soil level. We fitted our bark container, container lid, and tar collector together with clay, as we had some lying around, and as we believed it would harden sufficiently in the fire to create an air-tight seal. It would be possible to use many other types of sealant so long as they would withstand the fire.

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So, to assemble your tar kiln, bury the tar collector just short of ground-level deep, fix your bark container to it (if it isn’t already), and build a fire around this based with coal and then loaded with wood. We found it easiest to use the shell of a burned-out oil drum, which we also had lying around. This made it easy to control the fire and keep it evenly burning around the kiln.

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Allow the fire to burn for roughly three hours at a steady temperature. We were using dried oak cut-offs from a sawmill, so we reduced the final time down by at least half an hour, but most sources say three hours is sufficient. This amounts to about a fully-stacked wheelbarrow full of good dry wood. Protect from the rain and allow to cool overnight. The next day, carefully dig out your tar collector, making sure no dirt, char, ash or anything else falls into it. It should look like axle grease mixed with water, and there should be quite a lot of it.

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Raw birch tar. Note the charred birch bark in vessel below

Tip out the water that simply runs off the surface, and set the collector back over/next to the fire to boil off the rest. This could take some time, but the initial moisture bubbles off relatively quickly. The longer you do this, the finer the product. The boiling pitch now readily bursts into flame if the fire is too well-stoked, so have a kind of lid ready to extinguish the pot. In our experience it is best to trap something between the lid and the pot at this point – the pressure change inside the pan when the fire is snuffed out caused our ‘lid’ to be vacuum-sealed until it reached an adequate heat again.

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The top of the kiln (bark container) doubles as a smaller fire bucket for refining down the tar

The museum village sample seems to still have retained some water, and at least in the jar is by no means completely ‘set’. When you are happy, allow the tar to cool gently, at which point it will begin to solidify. Before this it will reduce down only marginally, so don’t worry about the consistency until the temperature is easing completely off. Boil some jars, dry them and fill with the slowly cooling tar while it is still pourable. Alternatively, twist a length of wood into the mixture smoothly and consistently to make a kind of oversized birch tar match-stick, which is easier to use and somehow looks more convincing.

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Birch Tar Technician #1 demonstrates the inedible nature of the product, no matter how much it resembles a lump of Blackjacks

We forgot to weigh the birch bark before we started, the pot before we buried it, and the containers before we finally filled them up with birch tar, so we cannot say with any accuracy what the ratio of bark to tar is (we were far too excited for any of this). A full 35l rucksack stuffed down with birch bark produces about 350g tar, including the stuff that is tricky to get out from the pot before it solidifies again. Furthermore, by treading a middle road between the highly contradictory information on birch tar production with common sense for a crutch along the way, we managed to produce a birch tar that was completely thermoplastic, i.e., one which sets rock hard on cooling, and therefore one that we believe a mesolithic man would have actually been covetous of.

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What’s more it is mid-September, and the hops have been ripening up beautifully, especially as they clamber over the derelict brick railway buildings north-east of Berlin. The area is of course not a hop-growing region; that’s done down in the Hellertau of Bavaria, where they regularly produce more hops per annum than the United States do. In these regions male hop plants are destroyed as not to compromise the harvest by pollination. Despite their beauty many of the wild hops found at the ripening period have already been pollinated anemophilously (the wind did it.), and these are not as good for use as non-pollinated hops. Luckily we have been growing aroma hops as an experiment this year, hardly wild, in fact a U.S. cultivar, ‘Cascade’, which are being dried on sheets of the financial section as I write.

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