Liquid smoke

A bottle of hickory liquid smoke sauce

Liquid smoke is a water soluble yellow to red liquid used for flavoring.^[1]

History

Pyrolysis or thermal decomposition of wood in a low oxygen manner originated prehistorically to produce Charcoal. Condensates of the vapors eventually were made and found useful as preservatives. The term wood vinegar for centuries was the popular term used to describe the water based condensates of wood smoke. Presumably, this is due to its utilization as food Vinegar. Pliny the Elder recorded in one of his ten volumes of Natural History (Pliny) the use of wood vinegar as an embalming agent, declaring it superior to other treatments he used. Widely recognized as the father of chemical engineering, another naturalist documentarian Johann Rudolf Glauber outlined in Furni Novi Philosophici ^[2] the methods to produce wood vinegar during charcoal making. Further, he described the use of the water insoluble tar fraction as a wood preservative and documented the freezing of the wood vinegar to concentrate it. Use of the French derivation, pyroligneous acid as a widely used term for wood vinegar emerged by 1788.^[3]

In the United States, the commercial distribution era of pyroligneous acid under a new term, liquid smoke that subsumed it began with E.H.Wright in 1895.^[4] Among Wright’s innovations were the standardization of the product, marketing and distribution. Wright’s liquid smoke and its modern day successors have always been the subject of controversy about what they are and how they are made. But in 1913 Wright, prevailed in a federal misbranding case. Case judge Van Valkenburg wrote:^[5]

The Government, in trying to show that this is not smoke produced by combustion, has shown that it is produced in exactly the same kind of way that is stated on that label. The fact is that they have produced something here which they say has something of the flavor and properties similar to the curative properties of smoke; they get it out of wood and they get it by distillation and it turns out to be a substance like, if not exactly identical with pyroligneous acid. Well, nobody could be deceived into thinking it was specifically what the indictment charges they are being deceived with. It is a thing which is produced in such a manner from the art and methods employed in it, that the application of the term “smoke” to it seems to me to be apt or applicable instead of deceptive, and it does not deceive in the sense this statute implies.

Historically, all pyroligneous acid products, Wright’s product and many other condensates have been made as byproducts of charcoal manufacturing which was of greater value. Chemicals such as Methanol, Acetic acid and Acetone have been isolated from these condensates and sold. But with the advent of lower cost Fossil fuel sources, today these and other wood derived chemicals retain only small niches. It was in 1959 that the era of modern condensed smoke based products began with the establishment of Red Arrow Products Company in Manitowoc Wisconsin.^[6] The important distinction marking this era from the past is the production of modern condensates to be used industrially as a replacement for smoking food directly with non-condensed smoke. Today there are many manufacturing locations around the world, most of which pyrolyze wood primarily to generate condensates which are further processed to make hundreds of derivative products. These are now referred to less so as liquid smoke products rather as smoke flavourings, smoke flavors, and condensed natural smokes.

Production

Liquid smoke and pyroligneous acid are terms used to describe the condensed products from the destructive distillation of wood. There are no standards of identity, prescribed production methods and no tests which distinguish between liquid smoke and pyroligneous acid; they can be considered to be the same. However, the numerous variables that are practiced during pyrolysis do lead to a wide range of compositions of the condensates.^[7] In addition many further processing steps by concentration, dilution, distillation, extraction, and use of food additives has led to the many hundreds of unique products on the market worldwide.

Wood, particularly hardwood, is by far the most widely used biomass pyrolyzed to make liquid smoke. Commercial products are made using both batch and continuous methods. Commercial products are made using a range of reactors from rotary calciners,^[8] heated screws,^[9] batch charcoal kilns,^[10] to fast pyrolysis reactors.^[11] The process type and conditions of processing lead to greater variances between the condensates than the differences between the common wood types that are in use. Variables such as feed rate, vapor residence time, particle size, oxygen infiltration, and temperature can have substantial effects on yield and composition of the condensates.^[12] Wide ranges of chemical composition are reported throughout the literature and unless the process and conditions are cited, there is limited utility of such results. Commercial manufacturers strive to control their manufacturing variables in order to standardize product compositions.

Water is added either during condensation or after to cause separation of three fractions.^[13] Once water is added, the aqueous phase becomes the largest and most useful fraction. It contains wood derived chemical compounds of higher chemical polarity such as those found in carboxylic acid, aldehyde, and phenol chemical classes. Many compounds together are responsible for flavor, browning, antioxidant and antimicrobial effects of smoke and liquid smoke. The smallest condensed fraction is the lowest polarity upper phase which a mix of phytosterols and other oily, waxy substances. The lower phase is commonly referred to as tar. It is an intermediate polarity mixture of phenolic polymers, secondary and tertiary reaction products,^[14] some of the water soluble polar compounds partitioned in the amount of which is governed by individual partition coefficients, water and the bulk of the polycyclic aromatic hydrocarbons. Wood tar has been used as a preservative, water repellent, antiseptic. Tar from birch was produced as a commodity product on large scale in northern europe. Today commercial liquid smoke products are still prepared from this phase.^[15]

Liquid smoke condensates are made commercially for the global meat industry in the U.S.and Europe and are regulated by those governments. Liquid smoke is still referenced as wood vinegar and is being made and used indigenously in many other locations such as Japan, China, Indonesia, Malaysia, Brazil, and Southeast Asia.^[16] The food regulatory regimes in these locations are either non-existent or not known outside of their jurisdictions.

Use

Liquid smoke is used as a seasoning to add a smokey flavor to various foods.

Aqueous and gaseous smoke can enhance seedling germination and emergence.^[17]

Safety

The European Food Safety Authority has found that some liquid smoke products contain In Vitro (in "petri dish" conditions) but not In Vivo (in a living organism) carcinogenic genotoxic compounds.^[18]

Regulation

The European Food Safety Authority (EFSA) is investigating the safety of liquid smoke as a food flavoring.^[19] One of the smoke flavorings being assessed, named Primary Product FF-B, raised concern. The EFSA Panel on food additives, flavorings, processing aids, and materials in contact with food (AFC) concluded that Primary Product FF-B can be regarded as weakly genotoxic in vivo (i.e. animal testing has shown it can damage DNA, the genetic material in cells). The Panel, therefore, could not establish its safety in use when added to food. However, no comparison was made against traditional smoked goods on the market.^[20] Primary Product AM 1 was described as potentially toxic to humans by the EFSA on 8 January 2010.^[21]

In a study by Guillén, Sopelana, and Partearroyo, it was discovered that different concentrations of polycyclic aromatic hydrocarbons (PAHs) were present in different liquid smoke flavourings depending on the type of tree used to produce the liquid smoke. The types of trees listed from those generally producing the highest concentration of PAHs to those producing the lowest concentration is: poplar, vine shoot, oak, cherry tree and beech woods. Liquid smoke produced with poplar wood produced the greatest amount of carcinogenic PAHs at 0.78 µg/kg); however, this is a small amount. The only PAH with an acceptable limit of 10 µg/kg, fixed by FAO/WHO, is benzo[a]pyrene, because it is highly carcinogenic. This was also found to be present in poplar and beech liquid smoke; however, the concentrations are well below the acceptable limit. The researchers also discovered that, independent of wood type, the concentrations of carcinogenic PAHs were the lowest when the temperature used during the production of the liquid smoke was 530-559 °C. This temperature range did not compromise the quality of the liquid smoke produced and is comparable to a previous research study that suggested 400-600 °C to be the optimal temperature range for wood pyrolysis.^[22]

References

External links

• Leffingwell & Associates, Smoke Flavor I. Includes chemical and chromatography information.