When sitting around a crackling campfire, you may notice that different types of firewood burn with different colored flames. The colors produced while burning various species of firewood actually have to do with the chemical composition of each wood type.
The Chemistry Behind Firewood Flame Colors
When wood burns, the main chemical reaction taking place is the combustion of cellulose and lignin – the primary components of all wood. As the wood heats up, these substances break down and undergo pyrolysis, releasing volatile gases that ignite and produce flames.
Different wood species contain varying ratios of chemical compounds like cellulose, hemicelluloses, and lignin. They also have diverse extractives content – compounds like fats, waxes, proteins, simple sugars, starches, oils, terpenes, and phenolics. It is these specific natural chemicals that influence the color of the flames when the firewood burns.
For example, wood with a high lignin content tends to burn with a yellow/orange hue. Softwoods like pine, fir, and cedar are high in lignin and create bright flames. Hardwoods like oak, maple, and hickory have less lignin, so they burn with a weaker yellow/orange color.
On the other hand, firewood containing more cellulose and hemicelluloses burns with a blue/white color. Aspen, poplar, and birch are hardwoods rich in these compounds, producing vibrant blue flames.
Certain extractives also impact the flame color. For instance, tannins found in oak result in darker red flames. Resins in pine firewood make the flames snap and crackle more. Oils in eucalyptus can make the firewood smell pleasant while burning.
Common Firewood Species and Flame Colors
Here is a breakdown of some typical firewood types and the flame colors they are known to produce:
| Firewood | Flame Color |
|---|---|
| Pine | Yellow/orange |
| Fir | Bright yellow |
| Cedar | Yellow/orange |
| Oak | Orange/red |
| Maple | Orange/yellow |
| Birch | Blue/white |
| Poplar | Blue |
| Aspen | Blue |
| Ash | Orange |
| Beech | Orange |
| Apple | Orange/yellow |
| Cherry | Orange/yellow |
| Elm | Orange/yellow |
| Hickory | Orange/yellow |
| Walnut | Orange/yellow |
| Mesquite | Orange/yellow |
As you can see, softwoods like pine, fir, and cedar tend to burn yellow, while hardwoods like birch, poplar, and aspen burn blue. Most other hardwood species produce flames in the orange/yellow/red color range.
Why Firewood Flame Color Matters
The color of the flames while burning firewood is more than just aesthetics – it can indicate how efficiently the fire is burning. Here’s why it matters:
- Yellow/orange flames mean there is incomplete combustion of the firewood. This results in smoke containing unburnt fuel, gases, and particulates. Not ideal for clean burning.
- Blue/white flames signify complete combustion and high efficiency. The wood is burning hotter and releasing the most energy.
- Red/dark black flames mean the fire is receiving insufficient oxygen. The smoke indicates wasted unburnt fuel.
- Crackling and snapping flames show presence of sap, resin, or oil. While this can look exciting, it often means smokier burning.
- Clean, lightly colored flames with just blue at the base lead to minimal smoke output for optimal air quality.
By knowing the typical flame color for a firewood species, you can better select and stack wood to promote a hotter, cleaner burn. For example, mix in some birch or poplar with other woods to get those ideal blue flames.
Tips for Burning Firewood Cleanly
Aside from choosing firewood wisely, here are some tips for burning it more cleanly and efficiently based on flame colors:
- Let firewood dry out to under 20% moisture before burning to reduce smoke.
- Split logs to 6 inches or less to speed drying time.
- Stack wood loosely for airflow to quicken moisture loss.
- Build a hot fire with lots of flames to combust wood gases completely.
- Ensure adequate air circulation for thorough combustion and consume smoke.
- Don’t smolder firewood; keep the flames actively burning.
- Use smaller diameter logs that can ignite easier and burn faster.
- Combine softwoods and hardwoods for a better balance of flames.
- Monitor the fire and add more wood before flames die down too much.
Following these guidelines while paying attention to the firewood flame colors can lead to far more efficient and cleaner wood fires.
Conclusion
The next time you have a burning firewood, take note of what color the flames are. The various chemical components of each wood species results in different flame hues. Softwoods like pine tend to burn yellow, while hardwoods like birch burn blue. The color gives you insight into how efficiently the fire is burning.
Aim for lightly colored flames with just blue at the base for minimal smoke. Letting firewood dry out completely and providing adequate airflow is key for cleaner combustion. Select a mix of softwoods and hardwoods in smaller diameter splits for best results. Pay attention to the flames and adjust the fire as needed. Knowing what firewood burns different colors helps you burn wood fires more efficiently and with less smoke.