When do you put out the fire?

I have been making my biochar in a TLUD for years.  It has a chimney. After it has been burning, you need to put out the fire, so that it doesn't all turn to ash.  In my first attempts, I think I let it go on too long.  I got a lot of ash and not so much biochar.  Obviously, I'm not talking about retorts, because they put the fire out by themselves. Eventually, I settled into quenching the fire with water when the flames were about 5-8 inches above the char.  I would get lots of char, almost no ash and some wood that wasn't completely burned.  Not a problem.  I would just save it and burn it in the next biochar burn.

However, yesterday, I was reading something interesting and didn't get to it until the flame was about 1 inch above the char.  I got tons of char.  There wasn't much more ash.  How much unburned wood did I get? None. Absolutely none.  This seems to be a better outcome than previously, but it makes me want to ask you people out there.  How do I know if that outcome is better or worse?

When do you quench the fire from your biochar?

John S
PDX OR

I'm not very particular about it because I'm not really trying to optimize the output, I'm usually pit burning to process brush piles so I just go with the flow of burning what I need to, letting it cook down just a bit further at the end, and quenching when I'm ready to move on. Usually that means a bit of ash and a few larger chunks of uncooked leftovers, neither of which bothers me since I'm just putting it all in the ground anyhow, not processing further.

If you are cooking batches in a dedicated setup, it sounds like you're on the right track of observing and adjusting based on your circumstances and aims. I'm sure you can get fairly scientific and try to reach a certain temperature for a set time...if that's important? What do you want to use the char for, may I ask?

I make biochar in a fireplace, by scraping the coals once the wood disintegrates into chunks (coals) and dumping them into a bowl of water. So there are no flames present at that point. I think as soon as the flames die back and it is just coals is my signal.

I am improving my soil.  It holds more water during our dry summers. It drains better in our wet winters.  The microbes hold onto more nutrients in the winter when the frequent rains wash out nutrients.  It enables more communication electrically, through the mycelium for nutrients to be shared among members of the soil food web.  It also tends to neutralize our naturally very acidic soils.
John S
PDX OR

John Suavecito wrote:When do you quench the fire from your biochar?

We are a group who meet to do burns in a flame cap burner. We extinguish the burn with a couple of buckets of cold water. I have only known this method. When the char is ready it needs to stop burning quickly to minimise ash and maximise char. Also, the shock cracks the char and makes it easier to break up.

The shock of the cold water also activates it, meaning it puffs it up and makes it a better home for the myriad of microbes that we're trying to nurture.
John S
PDX OR

1: Make a pile of brush & prunings about the size of a cow with no legs. Or with very short, tiny legs. 2: Dry it for a couple weeks/months. 3: Start burning it, gradually adding to the pile from another legless cow pile the same size. 4: Let the last ingredients burn a few more minutes. 5: When there's too much white relative to black, quench with cold water from a hose. 6: Crush into smaller pieces at that time, or months later. 7: Transfer to a serving container, gradually topping with garnishes of coffee grounds, spices, pee and other liquid loveliness. Yields two wheel barrow loads full.

That's an interesting technique. It's sort of like the trench method, but a bit different.
John S
PDX OR

I accidentally made some charcoal today. I was experimenting with trying to pop foxtail seeds in a sieve over an open flame, which didn’t work, when they caught fire and began burning vigorously. I saw an opportunity and so doused them as soon as the flames had died. I tasted some, and it was perfectly tasteless and the char was hard (silica in seed coats?)