For short extensions, add lit coals from a second chimney. For long cooks, use the snake or Minion method so most of the charcoal stays unlit and a small fire creeps through it over many hours. Top up before you run low, not after.
Step by step
Know how long a chimney lasts
A full chimney of briquettes gives roughly forty five to sixty minutes of genuinely useful high heat, then declines. Lump burns hotter for a shorter time. For anything past an hour, you need a plan.
For short cooks, add lit coals
To extend a grilling fire, light a second chimney and add the coals when they are fully ashed. Adding lit coals means no temperature dip and no off-smoke, unlike tipping in unlit charcoal.
For long cooks, build to burn slowly
For low and slow, do not light everything at once. Use the snake method in a kettle or the Minion method in a bullet, keeping most of the charcoal unlit so a small fire front travels through it for eight to twelve hours.
Top up before you run low
Feed the fire before it collapses, not after. A fire that has already died takes far longer to bring back than one you topped up on time. On a kettle, a hinged grate lets you add coals without lifting the food.
Control the burn rate with air
The more air you let in at the bottom vent, the faster the charcoal burns. For a long, slow fire, keep the bottom vent low; the fire will last far longer than a wide-open one.
Unlit fuel is the trick
The secret to a long fire is keeping most of the fuel unlit and letting a small fire eat through it slowly. Charcoal only burns where there is fire and air, so a pile of unlit briquettes with a few lit coals is a fuel store with a slow burn front. That is the whole idea behind the snake and Minion methods.
Reuse what is left
Whatever fire you build, close the vents at the end to snuff it and save the unburnt charcoal for next time. Over a season this saves a genuinely noticeable amount of fuel, especially with lump.
When you top up during a flavour-critical cook, add coals that are already lit and ashed from a second chimney. Tipping in raw unlit charcoal drops the temperature and gives off raw start-up smoke that can taint the food.
Common questions
How do I keep a fire going overnight?
Use the snake or Minion method with a full load of briquettes and the bottom vent low. Either will hold a steady low temperature for eight to twelve hours or more without touching the fuel.
Can I add unlit charcoal during a cook?
For short, casual cooks, yes, accepting a brief dip and some smoke. For anything where flavour matters, add lit coals from a second chimney instead.
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