INFOMANIA.CO.UK

Updated 25 May 2009 

If you are considering buying a barbecue you will have noticed that they burn either solid fuel – charcoal – or gas. So what are the differences and why would you buy one in preference to the other?

That wonderful barbecue flavour
Some people believe that charcoal is what gives a barbecue that ‘special’ barbecue flavour but in fact it does nothing of the sort. When charcoal burns it gives a steady heat and creates no particular smell. The delicious smoky barbecue flavour comes from fat dripping off the food and onto the hot charcoal. Or onto the hot metal or lava rocks in a gas barbecue…

Charcoal
Charcoal barbecues are cheaper than gas barbecues, for the simple reason that gas valves, taps and pipes cost money. They may also be a bit better for the environment – gas is a fossil fuel which releases greenhouse gases when it burns. Charcoal releases very similar gases when burnt but is not a fossil fuel – charcoal is made by heating wood in a sealed container so it carbonises instead of burning. When wood grows it absorbs greenhouse gases from the atmosphere so the manufacture and use of charcoal simply recycles greenhouse gases.

Disadvantages
There are two significant disadvantages to charcoal barbecues – the time it takes to get the charcoal burning steadily and the ash that has to be diposed of after the party is over. There are a number of ways to get charcoal burning properly. Most common is to use special lighter fluid or firelighters (the firelighters made for starting coal fires leaves a nasty chemical smell and taste). The charcoal needs to be made into small piles over the firelighters and, after setting fire to the firelighters, left until is is burning well and covered with a layer of grey ash. The coals can then be spread across the barbecue so cooking can begin. This process takes around 20-30 min.

A quicker way to get charcoal started is to use a charcoal ‘chimney’. This is a device like a large paint can with no bottom and a wire shelf 1/3 of the way up. The bottom of the ‘chimney’ is stuffed with newspaper, which is set alight, and the top filled with charcoal. There are lots of holes around the bottom, which allow air to enter. Hot air rises, so the flames from the burning paper rapidly heat the charcoal. The processtakesaround 10 min – much faster than using firelighters.

Gas
Gas barbecues typically come with two or three burners, although some have as many as five, perhaps including a side burner. Each burner has its own control knob so one part of the barbecue can be cooler than the others.  Not only that but auto-ingnition is a standard feature too except on the cheapest of models.  Virtually all gas barbecues have a hinged lid or hood, which provides a couple of significant benefits.:

•  Cooking is more consistent, particularly in breezy conditions
• The food is cooked in a smoky atmosphere, which gives it a great flavour

Many gas barbecues have a thermometer set into the lid, giving the cook a better idea of how fast the food is cooking and allowing the barbecue to be used as an oven. Upper-end models also have a glass panel set into the lid, allowing the cook to spot flare-ups when dripping fat catches fire and the food is at risk of burning. Unfortunately the windows are not quite as useful as they appear, as the glass  gets covered in a mixture of smoke and cooking fat which can be very difficult to shift.

Auto-ignition
Sometimes the ignition system is operated by the burner knobs and sometimes by a separate ignition button.Some gas barbecue ignition systems require batteries, others are piezo-electric. In the piezo-electric systems there is a piezo-electric crystal which generates a voltage when it is hit. The voltage is used to create a spark, which lights the gas. These system usually have a red ignition button that is quite stiff to operate. The button operates a small spring-loaded hammer which hits the crystal, generating  the spark.

Gas is very convenient to use. It is controllable and, once set up, a gas barbecue can go from cold to cooking in a few minutes. There is no need for firelighters and no messy ash to deal with. Gas is pretty cheap too – £15 of gas may last you a year or more if you are only a fine-weather barbecuer. On the other hand the bottles are very heavy and most suppliers charge a large deposit (around £30 for a 13kg bottle). FloGas used to supply gas in deposit-free bottles and their website currently says this for most bottles: ”No ‘Non returns’ charge applies to this cylinder”. Which might mean they still do!

For more information on gas barbecues see Barbecue gas – butane or propane?

bill Hints & tips barbecue, bbq, best, better, charcoal, gas

Buying a gas barbecue can be more than a little complicated. You think you have worked out what you want, then you discover there are two types of LPG (Liqueified Petroleum Gas) – Butane and Propane. Not only that, but the gas bottles come with different sized valves. And what on earth is Patio Gas?

Butane was more commonly used for barbecues than propane at one time but the situation appears to have reversed in recent years. In fact many, if not most, barbecues can use either butane or propane depending on the regulator valve fitted to the barbecue. Most barbecues now come fitted with a red propane regulator as standard. But is one gas better than the other?

A gas bottle with a butane regulator attached

Here is the rundown on the properties of different cooking gases:

For comparison, natural gas - as delivered to millions of homes via the gas mains - has the chemical formula CH4. When burnt, a cubic metre of natural gas will provide 38 Megajoules of energy.

Propane, chemical formula C3H8, produces 96 Megajoules of energy per cubic metre.

Butane, formula C4H10, produces 126 Megajoules of energy per cubic metre – far more than either natural gas or propane.

So butane must be better then? If only life were so simple. Inconveniently butane doesn’t work well at low temperatures. When too cool it stays as a liquid and the gas pressure drops. That means a butane gas cylinder will produce lower pressure once the bottle temperature drops below 10 degrees C. The bottles actually get colder in use, as heat is removed from the bottle when the liqud butane boils into the gas that comes out of the regulator. The higher the rate you use gas, the colder the bottle gets. Use it too fast in cool temperatures and the gas pressure can drop significantly. On one level it doesn’t matter - who wants to barbecue in chilly weather after all? How about someone who has suffered a power cut due to snowstorms?

A given quantity of butane will burn hotter than propane but in fact propane regulators release the gas at a higher rate to compensate. In fact many people will tell you that propane burns hotter. Both gases are heavier than air, which is one reason why barbecues have holes in their bottoms. If they didn’t, any leaking gas, (for example from a burner that has blown out) would build up in the bottom, ready to explode in the face of someone lighting the barbecue.

Gas bottles come in a variety of different sizes and, confusingly with different regulator fittings. The clip-on regulators used for barbecues are blue for butane, with a standard internal valve size of 21mm. Propane regulators are red with 27mm in internal size. That means that it is not possible to connect to a propane bottle using a butane regulator or vice versa.

A clip-on propane regulator

Typical bottles sizes vary from 3.9 kg to 13 kg but note that those are the weights of the amount of gas in the bottles, not the total weight. The total weight of most bottles is around three times the gas weight, so a 13kg bottle may weigh as much as 40 kg! BP have started selling Gas Light bottles which are made of glass-fibre reinforced plastic. They are translucent so it is possible to see how much liquified gas is left in the bottle. Needless to say they weigh a lot less too – around half as much as a steel bottle.

Note that in use the gas bottle has to be upright. The liquid has to be at the bottom of the bottle – attempting to use the bottle on its side could result in liquid gas being forced out. Which is one reason why barbecue gas pipes always seem a bit on the short side…

 Oh by the way Patio Gas – it just seems to be a marketing term for propane. It will work in both barbecues and patio heaters at all air temperatures, so is a good general-purpose bottled gas that is useful for all the gas-powered devices that are in common use on patios.

For information about the differences between gas and charcoal barbecues see Garden barbecues – charcoal or gas?.

admin White papers barbecue, butane, calorific, lpg, propane, regulator, value