Charcoal is a man-made product that is almost entirely elemental carbon. Meaning, charcoal itself won't "expire" or go bad and can last indefinitely.
However, if you're someone who uses briquettes, the additives used to make them can "go bad" or be rendered useless through evaporation - like Match Light Charcoal.
Charcoal is also porous and will readily absorb moisture. It should be kept in a cool, dry place to avoid moisture ingress.
Basic charcoal is made by burning a carbon-rich material like wood in a low-oxygen atmosphere with high heat - this process is called pyrolysis.
During this process, volatile compounds like water, methane, and tar are vaporized into the air. As a result, the wood is forced to decompose into a variety of substances, but mainly elemental carbon.
This resulting material will burn longer, more uniformly, and cleaner than seasoned wood; It is also much lighter (1/5 to 1/3 its original weight).
Wood charcoal is best described as brittle, lightweight, black, and porous.
Wood charcoal is made into two distinct forms, either lump charcoal or briquettes.
Lump charcoal has sort of become "fashionable" in the barbecue world - you'll often hear people call it traditional as it's only carbonized wood. As apposed to briquettes which contain additives.
In my opinion, you could equate it to eating "organic" versions of food.
However, for several brands, it's not just hardwood being used. Lump charcoal can be made from saw mill wood scrap, flooring materials, furniture, building materials, branches, forest scrap, hardwood, etc. All of which can be carbonized.
In my experience, every brand you buy from is different.
A great website I like to reference is the Naked Whiz. The website is owned by Doug Hanthorn and it's essentially a definitive guide to Lump Charcoal.
If you've bought a bag of lump charcoal - chances are, Doug's reviewed it and dumped it out onto a sheet to inspect the sizes of the pieces.
At the end of the day, lump charcoal is just carbonized wood. Meaning, you get less ash by-product. On the off-chance that the lumps get wet, they'll still easily ignite.
A charcoal briquette is made from a combination of materials. For example, wood particles, mineral char (heat source), and sawdust (aids in ignition). These materials are then mixed and pressed together to form one briquette.
Chemical additives are also commonly added to the mixture. The additives can help with things like taking shape, making ignition easier, and helping to control burn rates.
The most common additives are:
It's also not uncommon for "instant-light" varieties to be sprayed with a hydrocarbon solvent before bagging.
Charcoal has an indefinite life-span so long as it is stored correctly in a cool dry place. Meaning, it should be kept away from moisture and areas that are prone to temperature differences.
I'm from New England (an area notorious for temperature swings) and store my charcoal in my barn. I store it in the bag it comes in, away from sunlight, and the bag is rolled closed.
If I was someone who didn't barbecue often and needed a way to store it, I'd opt to put it inside in a cool, dry place in the packaging it came in.
You could also opt to store it in a bucket or plastic trash bin.
As noted above, charcoal is a porous material. Meaning, it will readily take on moisture.
However, charcoal taking on moisture doesn't mean that it's bad or somehow rendered inert.
To prove this, I took two Kingsford Original briquettes and put them in a bowl of water. Within 20 minutes, the briquettes sunk and were allowed to soak for the remaining 1 hour and 40 minutes of this test.
I also simulated a more "realistic" humid environment by putting a little bit of water into a Ziploc bag. I then placed four briquettes in the bag and laid it flat on my deck with the sun beating directly on it.
After two hours, I took the charcoal out of the water and the bag and placed them in my charcoal chimney.
The result: The charcoal still lit; Shocker!
There was a definite amount of white smoke as the water from the surface and inside the charcoal vaporized, but it still lit.
The resulting temperature from these five briquettes was 150F - pictured below on the lid thermometer.
Is there likely an amount of time where there is too much moisture? I'd wager to say, to a point.
However, even in this case where you've submerged the charcoal (a very rare occurrence) you could simply let the charcoal dry out - problem solved.
This is the same reason it's pointless to soak wood chips/chunks in water. The fire needs to burn off any added moisture (almost none penetrates) before it can smolder.
Lighter fluids for charcoal are either petroleum or alcohol based (methanol or ethanol). These substances can be applied to briquettes to create "Match-light" charcoal.
The reason Kingsford Match Light tells the user to "close tightly after use" is because these substances can and will evaporate; By closing the bag, you prevent this from happening.
A patent by GreenFlame Products LLC investigated alternatives to "match-light" substances. In the patent they discussed putting Kingsford Match-light Briquettes inside a Ziploc bag - similar to my scenario above.
The result was that the charcoal was no longer cable of being "match-lit."
"The Kingsford® Matchlight® charcoal was very effective if lit immediately after removing from the commercial packaging, but storage in the Ziploc® bags for even one day rendered the Matchlight® charcoal ineffective (see Table 2)."David E Moe, Reed E Oshel - 7/21/2015
Meaning, the Ziploc bag likely promoted a humid environment and caused these chemicals to readily evaporate.
However, that's not to say that the charcoal no longer "works" or that it went "bad."
Fortunately, there are a number of alternatives to lighter fluid.
In my opinion, the charcoal chimney is the best way to light charcoal. Be sure to check out my guide on how to use one.
Just to completely answer this question, I reached out to four brands of Charcoal that I regularly use: Royal Oak, Kingsford, FOGO, and Jealous Devil.
To each brand I asked:
"This might sound like a silly question but what is the shelf life (if any) of your charcoal? Could it be kept for long term storage?"
Royal Oak's Response:
FOGO Charcoal's Response:
All of these brands responded with the same sort of answers; Charcoal has an indefinite shelf-life so long as it's stored in a cool dry place and you avoid moisture.
As part of Kingsford's questioning, I also added:
"Do things like the chemicals in the match-light charcoal affect shelf-life?"
Which Kaitlyn noted above that Kingsford's Match Light charcoal does have a shelf-life of 1-2 years.