Charcoal pit Gropmila

As a blacksmith I am always in need of quality coal. But the charcoal for sale around here is not of high quality. It crumbles into little flakes and don’t really heat the metal the way I prefer. I decided to make a batch of spruce coal myself. They say it burns quicker, releasing more energy in a shorter period of time, and that they ash in a better way. The Swedish Järnverk of old, are said to have preferred spruce coal.
I have made coal before but never in the ground like this. I have no idea where I learned about the method, I could find no videos and almost no information about it on the internet. But as far as I remember someone during my childhood (perhaps at a boy scouts camp?), told me about the oldest known way of making charcoal, the Viking coal. It is called gropmila, and I assume it translates into English as charcoal pit. But googling that word gave me a load of less efficient char coaling methods. In a gropmila there is only fire in the beginning. The fire is strangled and air flow in and out controlled, that way wood is coaling in low temperature, making the end product comparably hard and heavy.
It took me some time to dig the hole and cut the wood, but then the first and largest batch of coal, about 350 liters, took only half a day to make. About half the wood I put in turned into coal but I was not satisfied, and put the uncoaled wood back in with some more. The second time around I kept it on a lower temperature and left it with the air-in fully open and air-out fully closed after about 12 hours of slow coaling. It did not give a better result.
The best result was achieved when the fire was pretty large to begin with, air-in fully open and air-out half open. The trick is to feel the smoke. It is supposed to be around 70 ˚C, warm enough to burn your hand, but only if keeping the hand in the smoke for a few seconds. An immediate burn means it is too hot, no burn say it is too cold. Burning hot and less thick, almost transparent smoke, means there is fire in the pit which is to be avoided.
I put some time stamps on the video but not much more. If you are interested in knowing more of the process, I would be happy to elaborate on it in the comments below. But you know as well as I do that the only way of knowing is to try it out yourself. Good luck.
Gustav Thane

[@gustavthane2233]

After my publication of this video I have been informed by coalers more experienced than me that a simpler way of doing it, reducing the amount of uncoaled wood, is to make an even larger fire. The pit can be dug and filled with only a large log fire in the middle, burning until the hole stack is almost completely coaled. At that stage the coal can be spread out throughout the whole bottom of the pit and a layer of wood stacked on top of it, about 20 cm deep. When the whole new layer of wood is on fire, a lot, another 20 cm of coal is added and the process is repeated, until the whole pit is full, and covered the same way as I did... with the difference that the middle square tussock is taken of as a chimney and air-out control. In the four corners, four round poles, preferably newly logged and wet could have been placed in the beginning of the process. When the tussocks are added on top of the coal pit the poles are taken out to allow an airflow down to the bottom of the pit. The old way. It would spend a bit more wood, but be worth it, since it would give more coal in the end.

[@joelscott7351]

The method is nice thanks, hopefully i will never have to try this but now i know how lol I like how you did this bare footed aswell

[@gustavthane2233]

Yeah, the joy of doing it is so much better than the need of doing it. It is always nice to get the full experience, the embodied experience, but when the process got intense and I had to dig new turfs quickly I was not as convinced digging barefooted was the best of ideas 😬

[@Kurokubi]

5:43 I'm sure you know this much and it's probably been stressed to you, but even so, there's no harm in hearing it again even if you've done it dozens of times (and I'm not saying you did anything particularly wrong or anything of the sort) But always remember to be very careful when walking on top of the covered pit, there's always a chance that the wood has turned to charcoal, is no longer "structurally sound", and will collapse under your weight (if it hasn't already, leaving a void underneath the dirt) and cause you to fall into a literal hell hole. Careful, prodding steps like you're walking on thin ice (or any other surface that would give under your weight)

[@gustavthane2233]

Thank you for the consideration. Yes you are right, that should have been spelled out as a warning, and now it is, thanks to you. When my son came by, half way through the process I did not allow him to walk on top of the pit for that very reason. But it is also important to compress the "roof" of the coal pit to ensure that there are no air pockets in there, risking to burn up the coal. In Swedish the sort of cavity leading to the risk of structural failure is called a "frät", I had one in the middle of the pit shown in around 6:50. But by compressing the pit roof a little bit all the time allowed me to keep track on it and feel how due it was, when the roof grew to weak above it I would walk on a more careful way and mostly, walk around it.

[@TypicalSwedeSWE]

Nice ! You deserve more views and subscribers ! Can you give me some more info about the size of the pit and how much kilos of wood you need to fill a batch and the approximate quantity of charcoal you obtain from a good batch ? Looking to make my own coal fore iron smelting...

[@gustavthane2233]

Thank you. Sure, the pit is about 1,05 metre deep, the sides are 0,95 m both and after the fist coaling the uppger 0,65 metre of wood was coaled. That is almost 600 lite of wood giving me just over 350 litres of coal. In The next itteration i did not count as carefully but it was less. The wood coaled was about as productive, even slightly more, maby 400 litres gave 250 litres of coal but more wood stayed uncoaled.

[@gustavthane2233]

An if you like it please share wherever you think others would appreciate it. I think the quiet format makes it fit in non-english and non-Swedish forums and groups where I have no chance to share it myself.

Gustav Thane sure ! Thanks for the info and good continuation !

[@xeonz474]

Vintage Story

[@Abbeio]

Har en hög gammal ved att bli av med så det här ska prövas 👍

[@gustavthane2233]

Javisst, klart du ska. Det är ju inte mycket arbete för så mycket kol.

[@Abbeio]

@@gustavthane2233 Nej precis. Vet du om det är lättare eller svårare att kola gammal ved? Fick med i stugan när jag köpte den. Lär minst vara 8 år.

[@gustavthane2233]

@@Abbeio Så vitt jag vet så är det bättre, såvida den torkats rätt o inte blivit rutten eller smulig av svamp i insekter. Det går mycket snabbare med torr ved o löper större risk att bli för varmt. Men jag skulle tro att det är mindre risk att få okolad ved som jag fick.

[@williammcdonald5086]

It seems like a lot of work. I’ve seen simpler methods.

[@gustavthane2233]

Yes, I beleave the pipe was unnessesary. And I could have put the wood in after the fire had allready coaled the first logs. But some of the simpler methods would not have produced as good forging coal. But it was a good video to use when starting a conversation with more experience coalers. Se my most rescent comment.

[@mnp5404]

@@gustavthane2233 The pipe was cool for airflow (were you referring to the chimney?). Plus, now they are there, the pit is dug, and so I imagine next time it would take a lot less work. I really enjoyed your precision and dedication. Very inspiring! Plus I could tell it's great quality by the sound of the finished pieces. The only regret i would have (and i have zip experience, so i'm only imagining things) is not being able to quench it. I've heard that opens it up quite a bit. Otherwise just wow!

[@gustavthane2233]

@@mnp5404 Nah, the pipe was for air in but the air did not spread out in the pit the way I wanted and made the coal in the middle burn up and still did not allow the coal on the lower sides to coal properly. I thought I could use it to get more control but I suppose it was not the perfect way of thinking about this process. I am happy you liked it. Thank you.

[@mnp5404]

@@gustavthane2233 Much appreciated! I love experimenting and don't mind messing up. It was a joy to watch, but it made me wish for a much younger body... lol! ;-)