Friday, November 4, 2011

What is "Meths?"

In the context of alcohol stoves, you may hear the term "meths" when people talk about fuel.  What is "meths?" (aka "metho") How is that different than Methanol?  How is that different than "Denatured" alcohol?

Generally, there are three types of alcohol:
  • Ethanol (ethyl alcohol)
  • Methanol (methyl alcohol)
  • Isopropanol (isopropyl alcohol)
Ethanol ("grain" alcohol) is what you get if you buy beer, wine, liquor, etc. It's not really in stove-ready concentration in most alcoholic drinks, although if you buy something like 190 proof Everclear, it will work very well as a stove fuel.  Ethanol is the byproduct of the fermentation of sugar.  Ethanol is used for drinking, as a fuel, and as a solvent.

Methanol ("wood" alcohol) is what you get if you buy HEET in the yellow bottle.  Methanol was first created by distillation from wood but is today typically created by chemical processes from methane (natural gas).  Methanol is used as a fuel, an antifreeze, a solvent, a denaturant for ethanol, and as a feedstock from which other compounds are produced.

Isopropanol is what you get if you buy "rubbing alcohol" or HEET in the red bottle.  Isopropanol is used as a solvent, in disinfecting pads, as an aid for swimmer's ear, a "gasoline dryer" (fuel additive to remove water), and as a feedstock from which other compounds are produced.

Alcohols as fuel:  Of the three types of alcohol, ethanol generally makes the best stove fuel. It has good heat content per gram, burns reasonably cleanly, and isn't overly toxic. Methanol isn't a bad fuel, but it has less heat per gram (which means you have to carry more to do the same amount of cooking) and is fairly toxic both in terms of breathing the fumes and skin contact. NEVER drink methanol.  Ingesting methanol may lead to severe nerve damage, permanent blindness, and death.  Isopropanol is a smokey mess when burned and generally makes a poor stove fuel.

Cold weather considerations:  When you're burning alcohol, you're really burning the vapor.  Methanol has a higher vapor pressure than ethanol which makes methanol vaporize more readily -- an asset in cold weather where sometimes it can be difficult to get ethanol to vaporize properly for burning. 

Denaturing:  As I said, unadulterated ethanol is the same stuff as in liquor. Governments typically tax liquor. For ethanol sold for purposes other than drinking, the ethanol is "denatured" (rendered undrinkable) by adding another substance, a denaturing "agent," to the ethanol so that it is not subject to liquor taxes. The generic name for ethanol with something added to render it undrinkable is "denatured alcohol".

Meths:  Outside the United States, methanol used alone is a common denaturing agent. Ethanol denatured by methanol is often called "methylated spirits" which, depending on what country you live in, is called "meths" or "metho" for short. Frequently, a dye, typically purple, is added to make it obvious that the alcohol is not intended for consumption.

In the United States, there isn't any regulation of what can be used to denature ethanol, and a variety of substances are used, typically in combination. In some cases the denatured alcohol is actually more denaturing agent than alcohol. 

Methanol is never suitable for drinking, so there is no need to "denature" methanol.

-Ethanol is a good stove fuel but to avoid liquor taxes it is typically denatured (rendered undrinkable) by adding some other substance or substances before it is sold for fuel or other purposes.
-"Meths" (or "metho") is one form of denatured alcohol.  Methanol is the denaturing agent for meths.
-Methanol is a different type of alcohol than ethanol and is a decent stove fuel but generally not quite as good as ethanol except in cold weather where methanol's higher vapor pressure facilitates combustion.

Hope that's helpful,


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