BBQs: Gas vs Charcoal

With the arrival of warmer weather, we cook outdoors more than ever – but when it comes to firing up the barbie, which is the more sustainable sizzler?

BBQs: Gas vs Charcoal

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The Aussie barbie is a national institution. Summer just wouldn’t be summer without the distinctive aroma of semi-burnt snags or beer-caramelised onions gently wafting its way across this great southern land.

But what of the environmental costs associated with our barbie-obsessed culture? The two most popular options to fuel your feast are gas and charcoal. So, when it comes to garden grilling, should you hit the bottle or burn the briquette?

Fuelling the fire
Liquefied petroleum gas (LPG) is used in a propane-only form when it’s used in barbecues. In Australia, 77 per cent of LPG is extracted from natural gas from areas including Bass Strait and Cooper Basin. The remainder is derived from oil-refining processes and therefore LPG is a non-renewable resource.

Charcoal, which is a dried, carbon-concentrated form of wood, is considered to be a renewable resource. However, the majority of charcoal available in Australia is imported from overseas. While some is produced from wood waste products, much – particularly lump charcoal – is produced from wood that is harvested from forests and this contributes to deforestation.

Once air-dried, the wood is pyrolysed – heated with little oxygen at 300-500°C – to produce charcoal. Many briquettes also contain polluting materials that have been added to aid ignition and slow burning, such as coal, borax and lighter fuel. The production phase accounts for 45 per cent of the total carbon footprint of charcoal.

Following production, both LPG and charcoal then need to be transported to your grill. Charcoal is light – a 3 kg bag is equivalent in volume to approximately 11 L, and is packaged in a 74 g bag. However, if the charcoal has been shipped from overseas it has a significantly greater transport footprint. Due to the heavy steel cylinder, a full tank of LPG weighs in at a whopping 27.5 kg, but most only travel nationally. The cylinders can also be re-used and recycled through the ‘Swap ’n’ Go’ scheme. For details, visit www.elgas.com.au/swapngo

Smoke signals
In a 2009 study that was conducted in the UK by Eric Johnson, an environmental consultant based in Switzerland, combustion of fuel during cooking was found to account for the majority of the carbon footprint for LPG barbecues. For charcoal, the second biggest factor in its footprint is combustion, after production.

For LPG, combustion accounts for about 66 per cent of its total footprint, with the biggest contribution coming from carbon dioxide (CO2). For charcoal, the figure is about 40 per cent. Particulate matter from charcoal combustion also contributes to air pollution and can contain traces of metals.

Johnson’s research concludes that the grilling footprint of charcoal is almost three times as large as that for LPG, with charcoal producing 6.7 kg of CO2 each grilling session, while in comparison LPG produces only 2.3 kg. The results boil down to the fact that LPG is more efficient than charcoal in its production, and also more efficient as a fuel for cooking. The research estimates that an average grilling session using charcoal is equivalent to driving a standard passenger car 35 km. For LPG, this falls to 13 km.

Johnson also questions whether charcoal should be given any credit for being renewable. “The ‘opportunity cost’ of biofuels, including wood, are often ignored,” he explains. “Leaving wood unharvested keeps carbon sequestered, but burning it does not, and burning LPG instead of wood releases far less carbon. It’s that simple.”

Accessory considerations
It’s not just the production or consumption of fuel that leaves a footprint when barbecuing. Most grill units are manufactured from steel, and those that run on LPG tend to be more complex and heavier than charcoal grills. There is also the production of those hefty steel gas cylinders that needs to be considered.
However, most LPG grills are self-igniting, while charcoal requires lighter fluid or firelighters. Disposing of charcoal ash that contains toxic additives is also a concern.

But the science suggests that, in the grand scheme of things, these factors are of little importance. Firelighters account for 7 per cent of the carbon footprint of charcoal grilling, while the more complex grill and gas cylinders contribute about 25 per cent to the carbon footprint for LPG.

The verdict
In terms of emissions, the verdict is clear – gas is the go. But if your delicate palate shudders at the thought of gas grilling, try to buy charcoal briquettes free of added nasties to reduce emissions and pollution. Australian-produced briquettes are also available, including charcoal produced from Queensland gidgee. Pure charcoal ash can be used as garden fertiliser, and be sure to refill gas cylinders and recycle old steel barbecues.

Finally, it is sobering thought that what you grill is probably more important than how you grill it. In 2011, researchers from TÜV Rheinland, in Germany, determined that up to 95 per cent of all emissions associated with barbecuing were related to food choice, and beef and cheese from methane-producing cattle were the worst offenders. By swapping a beef burger for a vegie burger, fish, or a kangaroo steak, you could reduce your barbecue’s carbon impact by nearly 20 per cent. So, throw another (vegie) snag on the barbie, and enjoy some summer grilling.