Does Dense Charcoal Burn Longer?
A Tale of Two Charcoals


Introduction
Just like there are Facebook legal experts and Facebook medical experts, there are Facebook charcoal experts. If we only had a nickel for every time we see someone post how great a charcoal is then look it up on The Lump Charcoal Database and see how rubbish it was, we'd be wearing more than a barrel for clothes. One of the more common examples of misinformation that we see posted is that dense charcoal burns longer than light charcoal. Does it? Well, our experience of testing dozens and dozens of brands of lump charcoal says otherwise. Here are the facts.


Exhibit 1 — Our Test Results
One of the types of charcoal we have seen repeatedly being touted as very dense and therefore long burning, is charcoal made from that old favorite, Quebracho Blanco. The notorious "axe breaker". "It's hard. It's dense. It's long burning." But is it really? As of this writing, we have conducted 126 controlled burn time tests of various brands of charcoal, including 6 brands made from Quebracho Blanco. Here's how they fared in the burn time category, ranked from best to worst:

BrandBurn Index¹Rank
Meat Head
16.60
 33/126
Jealous Devil
15.50
 46/126
B&B Texas Size XL
14.53
 65/126
Harder
14.07
 70/126
Original Charcoal Company
13.97
 73/126
B&B Expert's Choice (2004)
11.00
111/126

Note 1: Burn Index is an indication of how long the charcoal burned, with higher numbers corresponding to longer burn times. It is not the actual burn time recorded.

Burn test results for Quebracho Blance charcoal samples.


As you can see, many of these hard dense "axe breaker" charcoals did quite poorly in our burn time test. Even the best of this hard, dense type of charcoal fails to make it into the top 25% of all brands tested. So, it appears that hard, dense charcoal doesn't burn longer than other brands.

Which brands burn the longest and what are they like? Here are a few of the longest burning charcoals we have tested, ones that we specifically remember as being light. In fact, the Grove charcoal we remember being as light as styrofoam peanuts. At the time, it was the number 1 longest burning charcoal we had ever tested:

BrandBurn Index¹Rank
Lumber Jack
20.47
  4/126
Char-Broil Center Cut
20.25
  5/126
Big Green Egg Maple
20.17
  7/126
Grove
18.20
17/126

Note 1: Burn Index is an indication of how long the charcoal burned, with higher numbers corresponding to longer burn times. It is not the actual burn time recorded.

Burn test results for longer-burning charcoal samples.


So, it should be clear by now that hard dense charcoals simply do not burn as long a lighter charcoals. But wait! There's more!


Exhibit 2 — A Tale Of Two Charcoals
By far, the most damning evidence against this notion that hard dense charcoal burns longer came out of a rather unique opportunity we had recently to test two samples of charcoal. Two samples that came from the same manufacturer. Two samples that were made from the same type of wood. Two samples that were carbonized in the same kiln. So what was the difference between the two samples? One sample had been cooked to a high temperature, driving off more of the volatile compounds in the wood. It was a rather light charcoal, not very dense at all. The other sample was cooked to a lower temperature, and more of the volatile compounds remained in the wood. This sample was quite dense. So how did these two samples compare when it came to burn time?

Sample Density Burn Index¹Rank
Sample 1
(High Temperature, Light)
  8.5 lbs/ft³
19.80
10/126
Sample 2
(Low Temperature, Dense)
13.5 lbs/ft³
16.50
35/126

Note 1: Burn Index is an indication of the burn time, with higher numbers
corresponding to longer burn times. It is not the actual burn time recorded.

Burn test results for two samples cooked to different temperatures.


As you can see, the lighter charcoal burned far longer than the hard, dense charcoal. In case you were wondering, there were other differences between the two samples. One was that the lighter charcoal was a little harder to start than the hard dense charcoal. The other difference was that the lighter charcoal was more brittle and thus the box contained more chips and dust than the hard dense charcoal. But the real takeaway here is that the lighter charcoal burned significantly longer than the hard dense charcoal, a full 20% longer.


An Explanation
The reason for this seemingly backwards result has to do with what is cooked off when charcoal is heated to a higher temperature, the volatile components of the wood. The denser heavier charcoal has more moisture and a higher content of things like wood tars and wood alcohols. These volatiles add weight/density to the charcoal, but they don't burn as long as carbon does. So a pound of the lighter charcoal contains more long burning carbon than a pound of the denser charcoal.

If we might delve into the realm of reductio ad absurdum for a moment, here's an example that may sound silly but serves to illustrate the concept. Gasoline is lighter than water, weighing about 6 pounds per gallon. Water is denser than gasoline and weighs about 8.3 pounds per gallon. If we gave you a 1-gallon jug that contains a gallon of gasoline, it would weigh about 6 pounds. If we gave you a 1-gallon jug that contained 75% gasoline and 25% water, it would weigh about 6.6 pounds. But 2.1 pounds of that gallon (the water) won't burn. So even though the second gallon weighs more and is denser, the contents won't burn as long as the first gallon. That's what's going on with the heavier denser charcoal. Some of that weight doesn't burn as long as carbon does, so the heavier denser charcoal simply doesn't burn as long.


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