Reusing Charcoal: Risks, Myths, and Safety Precautions

🔥 Introduction

Charcoal is at the heart of BBQ cooking—regardless of country or culture—especially when it comes to low and slow smokes in Kamado grills, vertical smokers, kettles, and more. But one common and rarely questioned habit deserves our full attention: reusing previously burned charcoal.

I spent years relighting my BBQs with leftover charcoal from the day before. I’ve recommended Kamado grills so many times, often touting their efficiency in conserving charcoal—and saving money. But please, don’t do it anymore. The savings are just not worth it—for your health or your family's. Believe me.

I'm appalled that some of the biggest BBQ brands, especially in the Kamado world, still promote this practice on their websites. Even Google’s AI will tell you: "Yes, it's fine to reuse charcoal." Of course it will—AI can only repeat what it has learned. But are these brands truly aware of the risks? Or do they just not care?

🧪 What Happens Inside Used Charcoal

When charcoal burns for the first time, it’s never fully consumed. What remains includes:

partially oxidized carbon fragments
tar residues
possible additives or impurities (depending on charcoal quality)
trapped compounds like water, fat, nitrogen, etc.

When reheated—especially at low temps (<200°C / 390°F inside the dome)—these residues may break down slowly, releasing:

polycyclic aromatic hydrocarbons (PAHs)
volatile organic compounds (VOCs)
benzene, formaldehyde, acrolein
partially combustible tars

Without a strong flame or high-enough heat, these substances aren’t fully oxidized and can migrate into your food through smoke or re-melted fat.

🩻 Health Risks

The compounds released during low-temp reheating are anything but harmless:

PAHs (like benzo[a]pyrene) are Group 1 carcinogens according to IARC
Benzene, even at low doses, is a blood carcinogen (linked to leukemia)
Creosote, from tars, is toxic to liver and kidneys
VOCs, especially in closed environments (like a Kamado), can accumulate before being ventilated

The longer the cook and the more enclosed the setup, the greater the risk of toxic substances penetrating your food—especially when wood chunks or leftover fat are involved.

🧠 Scientific Evidence

Benzo[a]pyrene in low-temp cooks (Journal of Food Chemistry, 2019)
Significant BaP levels were found in slow cooks using reused charcoal, even with no visible flame.
Chemical analysis of recycled charcoal (Environmental Toxicology, 2021)
Using partially consumed charcoal increased PAH and carbonyl compound levels.
Effect of used embers on smoke toxicity (FAO Food Safety Report)
Smoke from reused embers had a more toxic chemical profile than fresh charcoal at equivalent temperatures.

🔬 Why It’s Worse at Low Temperatures?

Unlike a roaring flame:

The temperature is too low for complete combustion
Residues slowly release semi-volatile substances
Closed systems like Kamados or vertical smokers trap these fumes inside

Even if no flame ever touches your food, the stagnant smoke inside the cooker becomes a dangerous vector for chemical contamination.

❌ Common Misconceptions

Myth	Scientific Reality
"White charcoal is clean"	❌ False – It may still contain tar residues
"No direct contact = no danger"	❌ False – Harmful compounds travel through smoke
"We’ve always done it this way"	❌ Outdated – Scientific knowledge evolves
"I use high-quality charcoal"	❌ Even premium charcoal releases toxins if reused

✅ Practical Recommendations

DO:

Use fresh charcoal for long, low-temperature cooks
Choose additive-free, purified charcoal
Ensure good airflow (especially for Kamados & bullet smokers)
Clean greasy residues from your cooker
Add new charcoal on top of old if you’re running low

DON’T:

Fully reuse an old bed of embers
Cook long and slow with greasy, reused charcoal
Trap smoke inside your cooker for hours without ventilation

🌱 Safer Alternatives

Coconut shell briquettes – better thermal stability, fewer residues
Compressed hardwood logs – low PAH output with proper airflow
Cold smoke generators – isolate smoke from heat source (cold smoking)

📌 Summary Table

Best Practices	Avoid
Fresh, purified charcoal	Half-burned, greasy coals
Proper ventilation	Stagnant smoke in closed cookers
Regular cleaning	Reheated fat residues
Backed by science	Unquestioned tradition