Smoke, The Science of Smoke

Smoke, The Science of Smoke

The Science of Smoke brought to you by The National BBQ Association

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Smoke is comprised of the volatile parts of a fuel source. If you look at a piece of wood all the turpin, chemicals, and bad parts of the wood primarily are found in its bark. There are still some bad parts in a dried piece of wood with no back but much less. The wet fillers you find in wood are the parts that make your BBQ bitter, sour and have a bad taste. Mesquite has always been touted in the Green State to have a terrible taste exuded on the BBQ. Dried is better because most of the sap and wet composition  is gone. But what is better than dried wood. Carbonized wood. That is wood that has been made into lump charcoal. That is totally the good burning part of wood and none of the bad. Direct from ignition to clean blue smoke.  White puffy smoke has got moisture in it and hence the stuff that makes BBQ Bitter. If your buying charcoal or using wood that has to go through and hour of white fog then get rid of it. You can get lump charcoal that will transition straight to clear blue smoke and that is what makes great BBQ.

Why don’t you use ever green woods? Because the composition of that wood is full of carcinogens. That is substances that cause cancer. If its pine, cedar, spruce or any every green don’t put it in your fire box. Its dangerous to you and who ever eats that BBQ.

Let’s say you have a nice fire going, and it has burned down to the point where what you see is a collection of hot “glowing embers.” The fire is still producing a lot of heat, but it is producing no smoke at all. You might have gotten to this point either by starting with logs in a fireplace or by starting with charcoal. If you now toss a piece of wood, or even a sheet of paper, onto this fire, what you will notice is that the new fuel produces a lot of smoke as it heats up. Then, all of a sudden (often with a small pop), it bursts into flame and the smoke disappears.

If you have a fireplace or wood stove, or if you have been around a lot of campfires, this little scene is very familiar to you. It tells you a lot about smoke — let’s look at what is happening.

There are four things that you find in any piece of wood:

  • Water – Freshly cut wood contains a lot of water (sometimes more than half of its weight is water). Seasoned wood (wood that has been allowed to sit for a year or two) or kiln-dried wood contains a lot less water, but it still contains some. Poolonomics
  • Volatile organic compounds – When the tree was alive, it contained sap and a wide variety of volatile hydrocarbons in its cells. If you have read How Food Works, you know that cellulose (a chief component of wood) is a carbohydrate, meaning it is made of glucose. A compound is “volatile” if it evaporates when heated. These compounds are all combustible (gasoline and alcohol are, after all, hydrocarbons — the volatile hydrocarbons in wood burn the same way).
  • Carbon
  • Ash – Ash is the non-burnable minerals in the tree’s cells, like calcium, potassium and magnesium.

When you put the fresh piece of wood or paper on a hot fire, the smoke you see is those volatile hydrocarbons evaporating from the wood. They start vaporizing at a temperature of about 300 degrees F (149 degrees Celsius). If the temperature gets high enough, these compounds burst into flame. Once they start burning, there is no smoke because the hydrocarbons are turned into carbon dioxide and water (both invisible) when they burn.

This explains why you see no smoke from a charcoal fire (or a fire that has burned down to embers).Charcoal is created by heating wood to high temperatures in the absence of oxygen. That is, you take wood and put it in a sealed box of steel or clay and you heat it to about 1,000 degrees F (538 C). This process drives off all of the volatile organic compounds and leaves behind the carbon and the minerals (ash). When you light the charcoal, what is burning is the pure carbon. It combines with oxygen to produce carbon dioxide, and what is left at the end of the fire is the ash — the minerals.

Coke from coal is the same thing. Coke is coal that has been heated in the absence of oxygen to drive off the organics. The smoke that this process produces is actually very valuable — it contains coal tar, coal gas, alcohols, formaldehyde and ammonia, among other things. And all of these compounds can be distilled out of the smoke for use. You may have heard of methanol (a form of alcohol) referred to as “wood alcohol.” It used to be produced by distilling out of wood smoke.

The Science of Smoke

from Dr. Matt Lowrance, “The BBQ Doctor”


When I first started cooking BBQ I wanted to know what was going on chemically. I needed all the help I could get and I thought that if I understood what the basic science was behind smoking, I could produce a better product. I hit the books started cooking more and became an MBN trained BBQ judge. Here is what I found.

1: wood/charcoal is burned creating smoke which is particulate matter of the material burned.

2: This produces NO2 or Nitrogen dioxide. The more wood, the more smoke and the more NO2 produced. (don’t want to over do it! BITTER) This mixes with the surface of the meat and dissolves.

3: It becomes acidic losing an oxygen molecule and wanting to bind with something to become a more stable compound.

That led me to ask “what is in the meat that really wants oxygen?” The meat that we cook is muscle and, since it is no longer alive, it is without an active vascular supply to bring it oxygen via the blood stream in the hemoglobin molecule. So what’s in there? Myoglobin. That is the oxygen binding component in muscle that holds oxygen in the tissue. (When you exercise and get sore, you are pulling oxygen from the myoglobin making an acidic environment in your muscles. That’s why it hurts!!) This is similar to what we are doing with meat when we smoke it. Creating an acidic environment and allowing the meat to bind and pull this acid into it.

4: The myoglobin in the muscle tissue binds to the acidic nitrous created from the smoke introduced and dissolved into the surface of the meat. This creates the red color and that great flavor.

The absolute necessary element in BBQ and in any chemical reaction is energy. In this case it is heat. Low, slow and very controlled. That is what is so unique about southern BBQ.

Chuck, you’re on to something. Can you start to see why I am so excited about the cooking technique and especially the Stacker Smokers? They maximize the natural process of these reactions. The inside of the Stacker is the perfect environment for making this happen. The technique gets the natural flavors to come out. Adding a rub/marinade or whatever LATER in the cooking cycle not only adds flavor but creates a barrier and helps to seal this inside the meat. Like you always say…balance is still the key. The difficult part is controlling the heat and keeping moisture in the environment and I think we know how the Stacker does with that. The drawer system is the ultimate in control and the natural convection, water pan and the other elements of the smoker….well let’s just say I am more than impressed.

This isn’t the secret to winning championships. Or is it?

The fundamental elements of smoking and cooking are what cooks and teams need to know in order to understand what they are doing. Once these processes are understood at the basic level, I believe the doors fly open as to the possibilities with cooking BBQ. I think the teams that get this are the ones that are able to win and keep winning. The Stacker does better than any other I have ever seen at giving the most optimal environment for the physiology of smoking meat. It lets you blame only yourself for not winning.

Dr. Matt Lowrance
“The BBQ Doctor”

What is Smoke the Definition of Smoke

  1. 1.
    a visible suspension of carbon or other particles in air, typically one emitted from a burning substance.
    “bonfire smoke”
    synonyms: fumes, exhaustgasvapor; More

  1. 1.
    emit smoke or visible vapor.
    “heat the oil until it just smokes”
    synonyms: smolder, emit smoke; More

  2. 2.
    cure or preserve (meat or fish) by exposure to smoke.
    “smoked salmon”
    synonyms: curepreservedry More

Smoke is a collection of airborne solid and liquid particulates and gases[1] emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires (including stovescandlesoil lamps, and fireplaces), but may also be used for pest control (fumigation), communication (smoke signals), defensive and offensive capabilities in the military (smoke-screen), cooking (smoked salmon), or smoking (tobaccocannabis, etc.). Smoke is used in rituals, when incense, sage, or resin is burned to produce a smell for spiritual purposes. Smoke is sometimes used as a flavoring agent, and preservative for various foodstuffs. Smoke is also a component of internal combustion engine exhaust gas, particularly diesel exhaust.

Smoke inhalation is the primary cause of death in victims of indoor fires. The smoke kills by a combination of thermal damage, poisoning andpulmonary irritation caused by carbon monoxidehydrogen cyanide and other combustion products.

Smoke particles are an aerosol (or mist) of solid particles and liquid droplets that are close to the ideal range of sizes for Mie scattering of visible light. This effect has been likened to three-dimensional textured privacy glass[citation needed] — a smoke cloud does not obstruct an image, but thoroughly scrambles it.

Chemical composition[edit]

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed(April 2011)

The composition of smoke depends on the nature of the burning fuel and the conditions of combustion.

Fires with high availability of oxygen burn at a high temperature and with small amount of smoke produced; the particles are mostly composed of ash, or with large temperature differences, of condensed aerosol of water. High temperature also leads to production of nitrogen oxides. Sulfur content yieldssulfur dioxide, or in case of incomplete combustion, hydrogen sulfide. Carbon and hydrogen are almost completely oxidized to carbon dioxide and water. Fires burning with lack of oxygen produce a significantly wider palette of compounds, many of them toxic. Partial oxidation of carbon produces carbon monoxide, nitrogen-containing materials can yield hydrogen cyanide,ammonia, and nitrogen oxides. Hydrogen gas can be produced instead of water. Content of halogens such as chlorine (e.g. in polyvinyl chloride or brominated flame retardants) may lead to production of e.g. hydrogen chloridephosgenedioxin, and chloromethanebromomethane and other halocarbonsHydrogen fluoride can be formed from fluorocarbons, whether fluoropolymerssubjected to fire or halocarbon fire suppression agents.[2] Phosphorus and antimony oxides and their reaction products can be formed from some fire retardant additives, increasing smoke toxicity and corrosivity. Pyrolysis of polychlorinated biphenyls (PCB), e.g. from burning older transformer oil, and to lower degree also of other chlorine-containing materials, can produce 2,3,7,8-tetrachlorodibenzodioxin, a potent carcinogen, and other polychlorinated dibenzodioxins. Pyrolysis of fluoropolymers, e.g. teflon, in presence of oxygen yields carbonyl fluoride (which hydrolyzes readily to HF and CO2); other compounds may be formed as well, e.g. carbon tetrafluoridehexafluoropropylene, and highly toxic perfluoroisobutene (PFIB).[3]


Emission of soot from a large dieseltruck, without particle filters.

Pyrolysis of burning material, especially incomplete combustion or smoldering without adequate oxygen supply, also results in production of a large amount of hydrocarbons, both aliphatic (methaneethaneethyleneacetylene) and aromatic (benzene and its derivates, polycyclic aromatic hydrocarbons; e.g. benzo[a]pyrene, studied as a carcinogen, or retene), terpenesHeterocyclic compounds may be also present. Heavier hydrocarbons may condense as tar; smoke with significant tar content is yellow to brown. Presence of such smoke, soot, and/or brown oily deposits during a fire indicates a possible hazardous situation, as the atmosphere may be saturated with combustible pyrolysis products with concentration above the upper flammability limit, and sudden inrush of air can cause flashover or backdraft.

Presence of sulfur can lead to formation of e.g. hydrogen sulfidecarbonyl sulfidesulfur dioxidecarbon disulfide, and thiols; especially thiols tend to get adsorbed on surfaces and produce a lingering odor even long after the fire. Partial oxidation of the released hydrocarbons yields in a wide palette of other compounds: aldehydes (e.g. formaldehydeacrolein, and furfural), ketones, alcohols (often aromatic, e.g. phenolguaiacolsyringolcatechol, and cresols), carboxylic acids (formic acidacetic acid, etc.).

The visible particulate matter in such smokes is most commonly composed of carbon (soot). Other particulates may be composed of drops of condensed tar, or solid particles of ash. The presence of metals in the fuel yields particles of metal oxides. Particles of inorganic salts may also be formed, e.g. ammonium sulfateammonium nitrate, or sodium chloride. Inorganic salts present on the surface of the soot particles may make themhydrophilic. Many organic compounds, typically the aromatic hydrocarbons, may be also adsorbed on the surface of the solid particles. Metal oxides can be present when metal-containing fuels are burned, e.g. solid rocket fuels containing aluminiumDepleted uranium projectiles after impacting the target ignite, producing particles of uranium oxidesMagnetic particles, spherules of magnetite-like ferrous ferric oxide, are present in coal smoke; their increase in deposits after 1860 marks the beginning of the Industrial Revolution.[4] (Magnetic iron oxide nanoparticles can be also produced in the smoke from meteorites burning in the atmosphere.)[5] Magnetic remanencerecorded in the iron oxide particles, indicates the strength of Earth’s magnetic field when they were cooled beyond their Curie temperature; this can be used to distinguish magnetic particles of terrestrial and meteoric origin.[6] Fly ash is composed mainly of silicaand calcium oxideCenospheres are present in smoke from liquid hydrocarbon fuels. Minute metal particles produced by abrasion can be present in engine smokes. Amorphous silica particles are present in smokes from burning silicones; small proportion of silicon nitride particles can be formed in fires with insufficient oxygen. The silica particles have about 10 nm size, clumped to 70-100 nm aggregates and further agglomerated to chains.[3] Radioactive particles may be present due to traces of uraniumthorium, or other radionuclides in the fuel; hot particles can be present in case of fires during nuclear accidents (e.g. Chernobyl disaster) or nuclear war.

Smoke particulates have three modes of particle size distribution:

  • nuclei mode, with geometric mean radius between 2.5–20 nm, likely forming by condensation of carbon moieties.
  • accumulation mode, ranging between 75–250 nm and formed by coagulation of nuclei mode particles
  • coarse mode, with particles in micrometer range

Most of the smoke material is primarily in coarse particles. Those undergo rapid dry precipitation, and the smoke damage in more distant areas outside of the room where the fire occurs is therefore primarily mediated by the smaller particles.[7]

Aerosol of particles beyond visible size is an early indicator of materials in a preignition stage of a fire.[3]

Burning of hydrogen-rich fuel produces water; this results in smoke containing droplets of water vapor. In absence of other color sources (nitrogen oxides, particulates…), such smoke is white andcloud-like.

Smoke emissions may contain characteristic trace elements. Vanadium is present in emissions from oil fired power plants and refineries; oil plants also emit some nickel. Coal combustionproduces emissions containing aluminiumarsenicchromiumcobaltcopperironmercuryselenium, and uranium.

Traces of vanadium in high-temperature combustion products form droplets of molten vanadates. These attack the passivation layers on metals and cause high temperature corrosion, which is a concern especially for internal combustion engines. Molten sulfate and lead particulates also have such effect.

Some components of smoke are characteristic of the combustion source. Guaiacol and its derivatives are products of pyrolysis of lignin and are characteristic of wood smoke; other markers aresyringol and derivates, and other methoxy phenolsRetene, a product of pyrolysis of conifer trees, is an indicator of forest firesLevoglucosan is a pyrolysis product of celluloseHardwood vssoftwood smokes differ in the ratio of guaiacols/syringols. Markers for vehicle exhaust include polycyclic aromatic hydrocarbonshopanessteranes, and specific nitroarenes (e.g. 1-nitropyrene). The ratio of hopanes and steranes to elemental carbon can be used to distinguish between emissions of gasoline and diesel engines.[8]

Many compounds can be associated with particulates; whether by being adsorbed on their surfaces, or by being dissolved in liquid droplets. Hydrogen chloride is well absorbed in the soot particles.[7]

Inert particulate matter can be disturbed and entrained into the smoke. Of particular concern are particles of asbestos.

Deposited hot particles of radioactive fallout and bioaccumulated radioisotopes can be reintroduced into the atmosphere by wildfires and forest fires; this is a concern in e.g. the Zone of alienationcontaining contaminants from the Chernobyl disaster.

Polymers are a significant source of smoke. Aromatic side groups, e.g. in polystyrene, enhance generation of smoke. Aromatic groups integrated in the polymer backbone produce less smoke, likely due to significant charring. Aliphatic polymers tend to generate the least smoke, and are non-self-extinguishing. However presence of additives can significantly increase smoke formation.Phosphorus-based and halogen-based flame retardants decrease production of smoke. Higher degree of cross-linking between the polymer chains has such effect too.[9]

Find out more about Thousands of Grills and Smokers

Visible and invisible particles of combustion[edit]

Smoke from a wildfire

Depending on particle size, smoke can be visible or invisible to the naked eye. This is best illustrated when toasting bread in a toaster. As the bread heats up, the products of combustion increase in size. The particles produced initially are invisible but become visible if the toast is burned or cooled rapidly.

Smoke from a typical house fire contains hundreds of different chemicals and fumes. As a result, the damage caused by the smoke can often exceed that caused by the actual heat of the fire. In addition to the physical damage caused by the smoke of a fire – which manifests itself in the form of stains – is the often even harder to eliminate problem of a smoky odor. Just as there are contractors that specialize in rebuilding/repairing homes that have been damaged by fire and smoke, fabric restoration companies specialize in restoring fabrics that have been damaged in a fire.

Dangers of smoke

Smoke from oxygen-deprived fires contains a significant concentration of compounds that are flammable. A cloud of smoke, in contact with atmospheric oxygen, therefore has the potential of being ignited – either by another open flame in the area, or by its own temperature. This leads to effects like backdraft and flashover. Smoke inhalation is also a danger of smoke that can cause serious injury and death.

Many compounds of smoke from fires are highly toxic and/or irritating. The most dangerous is carbon monoxide leading to carbon monoxide poisoning, sometimes with the additive effects ofhydrogen cyanide and phosgeneSmoke inhalation can therefore quickly lead to incapacitation and loss of consciousness. Sulfur oxides, hydrogen chloride and hydrogen fluoride in contact with moisture form sulfurichydrochloric and hydrofluoric acid, which are corrosive to both lungs and materials. When asleep the nose does not sense smoke nor does the brain, but the body will wake up if the lungs become enveloped in smoke and the brain will be stimulated and the person will be awoken. This does not work if the person is incapacitated or under the influence of Drugs and/or alcohol

Cigarette smoke is a major modifiable risk factor for lung diseaseheart disease, and many cancers.

Reduced visibility due to wildfire smoke in Sheremetyevo airport (Moscow, Russia) 7 August 2010.

Smoke can obscure visibility, impeding occupant exiting from fire areas. In fact, the poor visibility due to the smoke that was in the Worcester Cold Storage Warehouse fire in Worcester, Massachusetts was the exact reason why the trapped rescue firefighters couldn’t evacuate the building in time. Because of the striking similarity that each floor shared, the dense smoke caused the firefighters to become disoriented.[10]

Smoke corrosion

Smoke contains a wide variety of chemicals, many of them aggressive in nature. Examples are hydrochloric acid and hydrobromic acid, produced fromhalogen-containing plastics and fire retardantshydrofluoric acid released by pyrolysis of fluorocarbon fire suppression agentssulfuric acid from burning of sulfur-containing materials, nitric acid from high-temperature fires where nitrous oxide gets formed, phosphoric acid and antimony compounds from P and Sb based fire retardants, and many others. Such corrosion is not significant for structural materials, but delicate structures, especiallymicroelectronics, are strongly affected. Corrosion of circuit board traces, penetration of aggressive chemicals through the casings of parts, and other effects can cause an immediate or gradual deterioration of parameters or even premature (and often delayed, as the corrosion can progress over long time) failure of equipment subjected to smoke. Many smoke components are also electrically conductive; deposition of a conductive layer on the circuits can cause crosstalks and other deteriorations of the operating parameters or even cause short circuits and total failures. Electrical contactscan be affected by corrosion of surfaces, and by deposition of soot and other conductive particles or nonconductive layers on or across the contacts. Deposited particles may adversely affect the performance of optoelectronics by absorbing or scattering the light beams.

Corrosivity of smoke produced by materials is characterized by the corrosion index (CI), defined as material loss rate (angstrom/minute) per amount of material gasified products (grams) per volume of air (m3). It is measured by exposing strips of metal to flow of combustion products in a test tunnel. Polymers containing halogen and hydrogen (polyvinyl chloridepolyolefins with halogenated additives, etc.) have the highest CI as the corrosive acids are formed directly with water produced by the combustion, polymers containing halogen only (e.g. polytetrafluoroethylene) have lower CI as the formation of acid is limited to reactions with airborne humidity, and halogen-free materials (polyolefins, wood) have the lowest CI.[7] However, some halogen-free materials can also release significant amount of corrosive products.[11]

Smoke damage to electronic equipment can be significantly more extensive than the fire itself. Cable fires are of special concern; low smoke zero halogen materials are preferable for cable insulation.

When smoke comes into contact with the surface of any substance or structure, the chemicals contained in it are transferred to it. The corrosive properties of the chemicals cause the substance or structure to decompose at a rapid rate. In some instances the chemicals are absorbed into the substance or structure that it comes into contact with, i.e. clothing, unsealed surfaces, potable water piping, wood, etc., which is why in most cases dealing with a structure fire they are replaced.

Secondhand smoke inhalation

Secondhand smoke is the combination of both sidestream and mainstream smoke emissions. These emissions contain more than 50 carcinogenic chemicals. According to the Surgeon General’s latest report on the subject, “Short exposures to secondhand smoke can cause blood platelets to become stickier, damage the lining of blood vessels, decrease coronary flow velocity reserves, and reduce heart variability, potentially increasing the risk of a heart attack” [12] The American Cancer Society lists “heart disease, lung infections, increased asthma attacks, middle ear infections, and low birth weight” as ramifications of smoker’s emission [13]

Measurement of smoke

As early as the 15th Century Leonardo da Vinci commented at length on the difficulty of assessing smoke, and distinguished between black smoke (carbonized particles) and white ‘smoke’ which is not a smoke at all but merely a suspension of harmless water droplets. Smoke from heating appliances is commonly measured in one of the following ways:

In-line capture. A smoke sample is simply sucked through a filter which is weighed before and after the test and the mass of smoke found. This is the simplest and probably the most accurate method, but can only be used where the smoke concentration is slight, as the filter can quickly become blocked.

Filter/dilution tunnel. A smoke sample is drawn through a tube where it is diluted with air, the resulting smoke/air mixture is then pulled through a filter and weighed. This is the internationally recognized method of measuring smoke from combustion.

Electrostatic precipitation. The smoke is passed through an array of metal tubes which contain suspended wires. A (huge) electrical potential is applied across the tubes and wires so that the smoke particles become charged and are attracted to the sides of the tubes. This method can over-read by capturing harmless condensates, or under-read due to the insulating effect of the smoke. However, it is the necessary method for assessing volumes of smoke too great to be forced through a filter, i.e., from bituminous coal.[14]

Ringelmann scale. A measure of smoke color. Invented by Professor Maximilian Ringelmann in Paris in 1888, it is essentially a card with squares of black, white and shades of gray which is held up and the comparative grayness of the smoke judged. Highly dependent on light conditions and the skill of the observer it allocates a grayness number from 0 (white) to 5 (black) which has only a passing relationship to the actual quantity of smoke. Nonetheless, the simplicity of the Ringelmann scale means that it has been adopted as a standard in many countries.

Optical scattering. A light beam is passed through the smoke. A light detector is situated at an angle to the light source, typically at 90°, so that it receives only light reflected from passing particles. A measurement is made of the light received which will be lower as the concentration of smoke particles becomes higher.

Optical obscuration. A light beam is passed through the smoke and a detector opposite measures the light. The more smoke particles are present between the two, the less light will be measured.

Combined optical methods. There are various proprietary optical smoke measurement devices such as the ‘nephelometer‘ or the ‘aethalometer‘ which use several different optical methods, including more than one wavelength of light, inside a single instrument and apply an algorithm to give a good estimate of smoke. Poolonomics

Inference from carbon monoxide. Smoke is incompletely burned fuel, carbon monoxide is incompletely burned carbon, therefore it has long been assumed that measurement of CO in flue gas(a cheap, simple and very accurate procedure) will provide a good indication of the levels of smoke. Indeed, several jurisdictions use CO measurement as the basis of smoke control. However it is far from clear how accurate the correspondence is.