Denatured alcohol or methylated spirits is ethanol that has additives to make it poisonous, extremely bad tasting, foul smelling or nauseating, to discourage recreational consumption. In some cases it is also dyed.
Denatured alcohol is used as a solvent and as fuel for spirit burners and camping stoves. Because of the diversity of industrial uses for denatured alcohol, hundreds of additives and denaturing methods have been used. The main additive has traditionally been 10% methanol, giving rise to the term "methylated spirits". Other typical additives include isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and denatonium.
In the United States, the Alcohol and Tobacco Tax and Trade Bureau (TTB), formerly known as the Bureau of Alcohol, Tobacco and Firearms (ATF), regulates sales of alcohol, more specifically ethanol. Spirits (liquor, wine, beer, etc.) are heavily taxed. In order to avoid paying spirits taxes on alcohol that is not meant to be consumed, the alcohol must be denatured per specific formulations given by the TTB. There are approximately 50 formulations provided by the TTB, most of which are indeed toxic to humans, but not all.
Denatured alcohol is not, in itself, a preferred product — that is, it is not something that would be normally demanded if given the alternative of normal ethanol. Denatured alcohol and its manufacture are a public policy compromise. The supply and demand for denatured alcohol arises from the fact that normal alcohol (which in everyday language refers specifically to ethanol, suitable for human ingestion as a recreational drink or extractive medium for medicinal tinctures) is usually very expensive in comparison with similar chemicals, being highly taxed for revenue and public health policy purposes (see sin tax). If pure ethanol were made cheaply available for fuel, solvents, or medicinal purposes, some people might drink it.
Denatured alcohol provides a solution to permit legitimate use and manufacture of ethanol, whereby cheap ethanol can be made available for non-consumption use without the risk of its being converted for consumption. The process creates an ethanol-containing solution that is not suitable for drinking, but is otherwise similar to ethanol for most purposes. As a result, there is no duty on denatured alcohol in most countries, making it considerably cheaper than pure ethanol. As a consequence, its composition is tightly defined by government regulations that vary between countries.
Different additives are used to make it difficult to use distillation or other simple processes to reverse the denaturation. Methanol is commonly used both because its boiling point is close to that of ethanol and because it is toxic. Another typical denaturant is pyridine. Often the denatured alcohol is dyed with methyl violet.
There are several grades of denatured alcohol, but in general the denaturants used are similar. As an example, the formulation for completely denatured alcohol, according to 2005 British regulations was as follows: 
Completely denatured alcohol must be made in accordance with the following formulation: with every 90 parts by volume of alcohol mix 9.5 parts by volume of wood naphtha or a substitute and 0.5 parts by volume of crude pyridine, and to the resulting mixture add mineral naphtha (petroleum oil) in the proportion of 3.75 litres to every 1000 litres of the mixture and synthetic organic dyestuff (methyl violet) in the proportion of 1.5 grams to every 1000 litres of the mixture.
- Per hectolitre (100 L) of absolute ethanol: 3 litres of isopropyl alcohol, 3 litres of methyl ethyl ketone and 1 gram denatonium benzoate.
Denatured alcohol is used identically to ethanol itself except for applications that involve ingestion. Un-denatured ethanol is required for food and beverage applications and certain chemical reactions where the denaturant would interfere.
Consumption and toxicity
Despite its poisonous content, denatured alcohol is sometimes consumed as a surrogate alcohol, which can result in blindness or death if (as was typical) it contains methanol. For instance, during American prohibition, Federal law required methanol in domestically manufactured industrial alcohols, and on Christmas and the two following days, roughly at the midpoint of that "Great Experiment", 31 people in New York City died of methanol poisoning. To help prevent this, denatonium is often added to give the substance an extremely bitter flavor. Substances such as pyridine help to give the mixture an unpleasant odor, and emetic (vomiting) agents such as syrup of ipecac may also be included.
- "Ethanol Denaturants". The Online Distillery Network. 22 November 1993.
- Naim Kosaric, Zdravko Duvnjak, Adalbert Farkas, Hermann Sahm, Stephanie Bringer-Meyer, Otto Goebel and Dieter Mayer in "Ethanol" Ullmann's Encyclopedia of Industrial Chemistry, 2011, Wiley-VCH, Weinheim. doi:10.1002/14356007.a09_587.pub2
- "The Denatured Alcohol Regulations 2005". Office of Public Sector Information. 2005.
- "Commission Implementing Regulation (EU) No 162/2013 of 21 February 2013". Official Journal of the European Union. 2013.
- Blum, Deborah, "The Chemist's War", Slate, 19 Feb. 2010
- Gates, Charlie, "Meths drinking on the increase", Stuff ..., 14 April 2010
- 27 CFR 20, regulations relating to denatured alcohol in the United States
- Specifications and licensing of methylated spirits in the United Kingdom
- European Community COMMISSION REGULATION (EC) No 162/2013 on the mutual recognition of procedures for the complete denaturing of alcohol for the purposes of exemption from excise duty
- HM Revenue and Customs: Production, distribution and use of denatured alcohol