The Chemistry of Smoking

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Things You Probably Do not Know About Smoking

When you begin to make contact with the world of barbecue it is almost natural to extend your experiences to smoking. This is a natural gesture, especially if you are starting your journey on a carbon device (for the owners of gas devices we had already faced specific strategies): you just need to take a handful of chips between the fingers, sprinkle them on the embers and wait patiently for the smoke to make its magic. As often happens with such intuitive processes, extreme simplicity leads to an inevitable detachment from the analysis phase. It is simply not necessary, it is not strictly functional to obtain the desired result. And it’s a pity. Cause to try to look at the process of smoking with a magnifying glass, splitting it into its parts, helps to better understand the mechanisms and to better govern the effects. Let’s try doing together.

Post Affumicazione 2The first and most intuitive distinction is essentially physical: the smoke is formed by a gaseous component, consisting mainly of carbon dioxide and water vapor, inside which a corpuscular element is suspended and which is moved by it. The things becomes complicated when we go into detail: the corpuscular element contains up to over 200 known elements and it is precisely this that generates the magic. Each essence has a different composition and can be richer in an element rather than another, generating in combustion a unique imprinting against the food invested by its effluvi. Let’s try to group them then for families and understand what contribution each one gives to the final result. As usual, since this is not a chemistry blog and I am far from being a speaker capable of supporting a speech in that field, we will limit ourselves to the analysis of the direct effects of their application in the world of grilling and of the kitchen and in doing so, just to further lighten the speech, we will open windows containing small or big curiosities on the subject. A sort of “not everyone knows that …” section from the Settimana Enigmistica (it’s a famous italian brain teaser magazine) related to smoking, that kind of information that will help you very little during the early hours of preparation of your cook off but that will help you a lot in the afternoon, when you’l spread your knowledge to your guests in front of a coffee and a limoncello.


That is, compounds that contain an OH hydroxide. There are many, but those that interest us are basically two.

Alcohols – The name will probably make you understand their behavior during smoking: Alcohol has a solvent, antiseptic and disinfectant power. They can assume long chain shape more effective antimicrobial, and short chain, more volatile. Alcohol is present in different sizes in all plant forms and their function in the barbecue is activated when they are distilled and modified by heat, resulting very effective on bacterial vegetative forms but are devoid of sporicidal capacity. Their action is done by denaturing the soluble surface proteins, damaging the cell protoplasm and consequently dehydrating them (do you know the effect of when you try to clean a surface by passing the alcohol with a cloth?). So let’s summarize what we learned about Alcohol:

  1. Different woods are characterized by a different proportion between long chain and short chain alcohols, so their action in barbecue terms will be different depending on the type of wood used
  2. Alcohol (especially long-chain ones) are very effective for breaking down the surface bacterial load of foods. On the other hand, they do not have any effect on the spores
  3. Alcohols (especially short-chain ones) are highly volatile. This is the reason why the barbecue changes its perception over time and for which it is said that the barbecue the next day is better: the sour part of the alcohol disperses, leaving the aromatic part brought by the other elements.
  4. Alcohol will contribute to superficially drying the meat placed in smoking.

An Alcoholic Barbecue

Alcohols also includes Methanol, a wood distillate with very low boiling point, liquid and easily soluble in water, with characteristics very similar to Ethanol, which instead naturally forms during the fermentation of wine and for this reason widely used in 80s for food frauds in the sector

Phenols – They are very reactive molecules that are reversibly combined to proteins through the binding of Hydrogen H, which then becomes irreversible through subsequent oxidation. They therefore act by modifying the surface protein structure, altering both the enzymatic processes and the cellular respiration. The phenols also have a high antimicrobial power, which combined with the action previously described, make it a powerful sporicide, able to inactivate also Mycobacterium Tubercolosis and Bacillus Anthracis. The Phenols are colorless compounds but with highly recognizable aromas that often remind the many spices that are usually rich of it. So let’s summarize what we learned about the phenols:

  1. The phenols help alcohols very well on the preservation action of smoke on food by adding a sporicide to the antibacterial action.
  2. The Phenols modify the surface structure of smoked foods.
  3. The phenols help to naturally make many of the spicy aromas that you recognize in barbecue cooks. The Flavor and Aroma of smoke derives in large part from the phenols.

From the Pyramids to the Smoke Box

Among the phenols there's also the Guaiacol, a substance very present in the distilled cedar resin, used by the ancient Egyptians as ointment to be applied on the deceased as the first phase of the mummification process

A Brisket a day...

The antiseptic power of the Phenols has been recognized for a long time, so much so that the Phoenician Acid was the first disinfectant used by Pasteur for surgical wounds

The Rib goes where the tooth hurts

Among the phenols figure also Eugenol, highly present in the cloves and in the cinnamon and discreet anesthetic, so much to be used in antiquity in dentistry to treat the caries.

Carbonyl compounds

That is, compounds that contain a Carbon and an Oxygen atom joined by a C=O double bond. They mainly have two functions: a high degreasing power combined with an excellent antibacterial capacity. The result is the characteristic dark patina with an oxidized appearance that forms on smoked foods. You can see it more clearly when smoked without applying any rub.

Pit sweet Pit

Among the Carbonyl compounds is also Vanillin, the most important ingredient in the confectionery industry. Even today the most economical industrial method to obtain vanillin is the controlled oxidation of lignin, discarded in the paper processing process

Barric Barbecue

The toasting stage of the wine barrels production involves the distillation of the lignin and the consequent production of Vanillin. This is why one of the distinguishing features of wines matured in barriques, where the transmission of elements from the wood is more marked, is the hint of vanilla

Organic acids

That is, compounds that contain the carboxylic group -COOH. Also in this case the name already says a lot about their behavior: the acids lower the superficial Ph of the foods, or they naturally develop the antibacterial conditions that are at the base of the modern techniques of packaging long-life products. In other words it is cause (also) of the acids that the smoking plays its own natural preservative towards the food.


That is, compounds that contain multiples of Isoprene. In the Barbecue area they essentially provide a contribution in terms of aromatization and in forming a characteristic film on smoked foods.

The SmokyBuilding

Among the compounds of isoprene naturally present in living beings there are also Steroids, derivatives of Triterpenes

Polycyclic Aromatic Hydrocarbons (PAH)

They are molecules characterized by the presence of condensed aromatic rings. They present a very high boiling point and a very low solubility in water. Typically they are formed in the combustion of organic molecules at very high temperatures but not high enough to complete the pyrolysis and therefore constitute a waste of it. Their contribution is essentially aromatic, contributing to the typical “roasted” smell of grilling, the one referable to the concept of “natural smoking” which is recognized as the distinctive element of a cooking on the grill compared to an equal one in the pan. This is a very large class that includes among others the famous Benzopyrene and Dimethylantracene. To many of you these terms will be familiar because they will remind you to have heard condemning their carcinogenicity.

Said so, the thing would sound quite alarming if it were not that the PAHs typically develop between 400° C and 900° C, where clearly this refers to combustion temperatures and not that of the cooking chamber. In other words we could say that the conditions we have to look for to minimize the problem are those in which there is no burning flame in the embers. I do not want to say that PAHs in the other cooking conditions are absolutely absent, but simply that we don’t have to exaggerate with alarmism. I’ll give you an example:

It is a well-known fact that Basil is very rich in Methyl-Eugenol, which has proved to be potentially carcinogenic. But what exactly does “very rich” mean? “Very rich” compared to what? It could be assumed that Basil is much richer than the average of the other plants but nothing is said about the limit that can be absorbed by the organism without causing any damage. I have no specific data to provide (more than anything else because I do not have time to look for them, but I invite you to do it if you want and then compare) but knowing how the world of information works, I am convinced that you would find out that to have some influence on health, you should eat a pallet of pesto a day. On a national product-pride like Basil, no one would ever dream of writing nonsense sentences like “pesto is carcinogenic” or “basil on pizza margherita is carcinogenic”. In other less “troublesome” areas, the freedom to open the mouth and give vent to it becomes a right recognized to everyone. The moral is: do not be fooled, always ask the reason for the irrefutable truths that are told and think with your own head. But let’s go back to our smoking: in case of direct cooking we are careful not to incur flames and burns, in the others there must not be a concern about the production of PAHs higher than that of other commonly accepted cooking.

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Let’s try now to make the most of this information, drawing conclusions from which to derive some rules to smoke at best:

  1. Most of the reactions described above occur as a result of the distillation of the lignin components by the heat of our device. Each one does so at a different temperature, naturally lower than a significant production of Benzopyrene and Dimethylantracene. In general, however, we could say that the effectiveness of smoking is growing as the temperature increases. This explains why cold smoking requires so many hours to produce its effects. The other elements to be taken into consideration, however, are that the effects of the smoking are only on the first superficial millimeters, a little like the marinade and the brine and that the most important aromatic component, that given by the phenols will be fixed with the coagulation of proteins, which will happen as quickly as the temperature will be high. Ultimately, the best smoking will be a Trade Off between temperatures high enough to activate as many reactions as possible but low enough to allow enough time for meat to be adequately influenced. This is why a high temperature smoke (ex 180° C) is absolutely less evident than one in Low & Slow and here is what the Hot&Fast school of thought is based on, which aims to raise temperatures to a level where the “roasted” contribution of PAHs (summed to a higher level of Maillard Reaction) is maximized while remaining on timing appropriate to exploit the advantages of medium-low temperature cooking.Post Affumicazione Brisket 2
  2. When we start to smoke the cooking chamber is filled with a thick blanket of smoke. Around any object wrapped in a stagnant blanket, a layer of air thick one or two millimeters is formed, called a “boundary layer”. The corpuscular element moved in the smoke thus “slides” on the boundary layer, depositing very little along its passage. The presence of a rub on the surface helps to make it more irregular and consequently, more “gripping”. The rub so not only contributes to create the bark but also to improve the effects of smoking and the more rub is coarse and more this will be clinging to the corpuscular element of smoke.
  3. The smoke condenses on the surfaces the more there is difference in temperature between the two elements. And the more condensation the greater the deposited corpuscular element will be. It is so intuitive that the colder food will enjoy more intense smoke. The same can be said for wet food (see water smoker and mopping): the water will never exceed 100° C by definition and until it is present, it will ooze by lowering the surface temperature of the food and increasing the effects of ‘smoke flavoring.
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  4. Regardless of the temperature reached by the cooking chamber, the parameter to measure the quality of the smoke will be the level of combustion of the power supply. Sorbed embers will not allow the wood to reach the temperature sufficient to trigger the distillation of its components. When you start to smoke then, to make the most of the smoke, add wood only with the perfectly stabilized smoker and with the embers still perfectly alive, without ashes.

Now you’re ready to better understand what happens when you add a handful of chips or a chunk to your smoker and get the most out of your smoking. You’re ready for your 2.0 smoking?

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