Fruit-based Terms

Smoke is formed ... When fat drips onto hot charcoal, wood, or another heat source, it can pyrolyse (thermally decompose) and undergo incomplete combustion. The resulting smoke contains a complex mixture of compounds, some of which can condense or adsorb onto the food.

The main groups of concern are:

• Polycyclic Aromatic Hydrocarbons (PAHs) — including compounds such as:
  • benzo[a]pyrene
  • benzo[a]anthracene and
  • chrysene
  
  Some PAHs are carcinogenic or mutagenic. They are particularly associated with fat dripping onto flames or very hot coals and then being carried back to the food in smoke.
• Oxygenated Polycyclic Aromatic Hydrocarbons (PAHs) and other combustion products: Partially oxidized PAHs and related compounds can form during incomplete combustion.
• Aldehydes and ketones: Thermal breakdown of fats can produce compounds such as:
  • acrolein
  • formaldehyde and
  • acetaldehyde
  Some are irritating or toxic, although their deposition onto food generally presents less danger than their presence in the smoke inhaled around a barbecue.
• Volatile organic compounds (VOCs): VOCs include various hydrocarbons and oxygen-containing compounds produced from the decomposition and combustion of fat, wood and other organic material.
• Particulate matter/soot: Microscopic carbon-rich particles can become coated with organic compounds and settle on the food. These particles can carry PAHs and other combustion products.
• Phenolic compounds: Phenolic compounds are present particularly when wood or charcoal smoke is involved. Phenols and related compounds contribute strongly to the characteristic smoky flavour; some are relatively benign at typical dietary exposures, while others can be irritating or toxic at higher exposures.
• Nitrogen-containing compounds: Depending on the food and combustion conditions, smoke can contain compounds such as nitriles and other nitrogen-containing products.

Dripping fat is significant because the fat doesn't simply evaporate and land back on the meat unchanged. At the very high temperatures around the coals or flame, triglycerides and their breakdown products can undergo further cracking, oxidation and recombination, producing a much more complicated mixture.

Also, flames aren't necessary for dripping fat to create smoke. Fat contacting very hot charcoal can generate smoke even without a visible flame.

The amount deposited on the food depends strongly on:

• how much fat reaches the heat source
• the temperature
• whether flames are produced
• the type of fuel
• cooking duration
• distance from the heat, and
• how smoky the cooking environment is

Generally, visible smoke and repeated flare-ups mean substantially more opportunity for combustion products to reach the food.

A simplified sequence is:

fat → hot surface/flame → thermal decomposition + incomplete combustion → smoke → smoke contacts cooler food → compounds condense/adsorb onto food