Curious question about re-using charcoal

[T Bounds]

Friends,

I've been trying for the past 6 or 8 months to be more conscientious about closing the vents on my kettle or wsm to extinguish the coals and reuse them. I've had no problems, except the mess that comes from dealing with ash covered coals. Anyway, recently when I have been reusing coals on my kettle for steaks, chicken, burgers, whatever, I have noticed that my fires have been significantly hotter. I put all the recycled coals in the chimney starter first, then whatever new coals I think I need, and light them using a weber starter cube. When the whole chimney is ready I dump them out and prepare to cook. That's when I notice the extra heat. I'm convinced something is up, but I cannot say what it is. Has anybody else noticed anything like this effect? I'm very curious about this experience. Thanks for any responses.

 

[TroyRedington]

i re-use unspent charcoal as well and have also had similar observations.

i've noticed that previously burned coal tends to ignite easier and quicker - but instead of flaming up and then turning to ember, it simply goes straight to ember.

combine that with the increased surface area of many small chunks of charcoal compared to fewer large chunks of fresh - it will produce more heat and burn faster/hotter.

i'd hypothesize that breaking up the chunks of fresh charcoal to give them more surface area would produce the same effect.

 

[Darrel Williams]

I have 3 theories:

1) The first burn reduces the moisture content of the coals so that they burn more quickly/hotter the second time around.

2) The partially spent coals are smaller, so they pack tighter in the chimney, and thus the chimney holds a greater amount of coals by weight than a chimney full of only new coals. More mass = more heat.

3) Smaller coals have more surface area to mass ratio, and thus burn quicker, and hotter, but do not have the longer duration of new coals.

 

[Regina S]

Great explanation Darrel! Makes sense to me on all 3 reasons! I never thought of it that way, thanks for pointing that out.

 

[Davo]

I think there may be merit in those theories but I also suspect that the reason for them becomming hotter than the first time is because the heat hadn't reached the core of the briquette/coals and when you use them the 2nd time around, due to the outer areas and smaller diameter, theres not as much to heat up before the heat can successfully reach the inner core of the coals and once it reaches there, it's the upmost peak of it's intensity.
Even with lump Charcoal, yes it lights up faster and is intense depending on the wood type,but it's not untill the heat reaches the inner core, that it reaches it's greatest intensity....depends on the denseness of the charcoal in question as they all differ.
Here in Australia I find that red gum burns very hot very quick and the heat gets to the core very quick but woods like gidgee has a very dense slow burn quality and it takes a long time for the heat to reach the core.

Cheers

Davo