Liquid smoke is a water-soluble yellow to red liquid used as a flavoring to substitute for cooking with wood smoke. It can be used to flavor any meat or vegetable. It is available as pure condensed smoke from various types of wood, and as derivative formulas containing additives.
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. For centuries, water-based condensates of wood smoke were popularly called "wood vinegar", presumably due to its use as food vinegar. In 1658, Johann Rudolf Glauber outlined 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 term "pyroligneous acid" for wood vinegar emerged by 1788. In the United States, in 1895, E. H. Wright inaugurated the era of commercial distribution of pyroligneous acid under a new name, liquid smoke. Among Wright's innovations were the standardization of the product, marketing and distribution. Wright's Liquid Smoke, since 1997 owned by B&G Foods, and its modern-day successors have always been the subject of controversy about their contents and production, but in 1913, Wright prevailed in a federal misbranding case. Case judge Van Valkenburg wrote:
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. With the advent of lower cost fossil fuel sources, today these and other wood-derived chemicals retain only small niches. 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 as liquid smoke products, and instead as smoke flavorings, smoke flavors, and natural condensed smoke.
Production The condensed products from the destructive distillation of wood are called "liquid smoke" or "pyroligneous acid". There are no standards of identity, prescribed production methods, or tests which distinguish between liquid smoke and pyroligneous acid; they can be considered to be the same. However, the numerous variables that are manipulated during pyrolysis do lead to a wide range of compositions of the condensates. In addition, implementation of many further processing steps by concentration, dilution, distillation, extraction, and use of food additives has led to the many hundreds of different 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, heated screws, batch charcoal kilns, to fast pyrolysis reactors. 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. 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. 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 the 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, 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, and 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. Liquid smoke condensates are made commercially for the global meat industry in the U.S. and Europe and are regulated by governments. Liquid smoke is still referred to as wood vinegar, and is made and used indigenously in places including Japan, China, Indonesia, Malaysia, Brazil, and Southeast Asia.
Use
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