Moonshine was originally a slang term for high-proof distilled spirits that were usually produced illicitly, without government authorization.  In recent years, however, moonshine has been legalized in various countries and has become a commercial product.
Legal in the United States since 2010, moonshine is defined as "clear, unaged whiskey",  typically made with corn mash as its main ingredient.  Liquor control laws in the United States always applied to moonshine, with efforts accelerated during the total ban on alcohol production mandated under the Eighteenth Amendment of the Constitution. Since the amendment's repeal and moonshine's recent legalization, the laws focus on evasion of taxation on spirits or intoxicating liquors. Applicable laws are enforced by the Bureau of Alcohol, Tobacco, Firearms and Explosives of the US Department of Justice. Enforcement agents were once known colloquially as "revenooers".
Moonshine is known by many nicknames in English, including white liquor, white lightning, mountain dew, choop, hooch, homebrew, shiney, white whiskey, and mash liquor. Other languages and countries have their own terms for moonshine (see Moonshine by country).
When it was illegal in the United States, moonshine distillation was done at night to avoid discovery.  It was especially prominent in the Appalachian area. White whiskey most likely entered the Appalachian region in the late 18th century to early 1800s. Scots-Irish immigrants from the province of Ulster in the north of Ireland brought their recipe for uisce beatha, Gaelic for "water of life". The settlers made their whiskey without aging it, and that is the recipe that became traditional in the Appalachian area. 
By the early 20th century, moonshine became a key source of income for many Appalachian residents because the limited road network made it difficult and expensive to transport corn crops. As a study of farmers in Cocke County, Tennessee, observes: "One could transport much more value in corn if it was first converted to whiskey. One horse could haul ten times more value on its back in whiskey than in corn."  Moonshiners in Harlan County, Kentucky, like Maggie Bailey, made the whiskey to sell in order to provide for their families.  Others, like Amos Owens, from Rutherford County, North Carolina, and Marvin "Popcorn" Sutton from Maggie Valley, North Carolina, sold moonshine to nearby areas. Sutton's life was covered in a documentary on the Discovery Channel called "Moonshiners". The bootlegger once said that the malt (a combination of corn, barley, rye) is what makes the basic moonshine recipe work.  In modern usage, the term "moonshine" still implies the liquor is produced illegally, and the term is sometimes used on the labels of legal products to market them as providing a forbidden drinking experience.
Poorly produced moonshine can be contaminated, mainly from materials used in the construction of the still. Stills employing automotive radiators as condensers are particularly dangerous; in some cases, glycol produced from antifreeze can be a problem. Radiators used as condensers could also contain lead at the connections to the plumbing. Using these methods often resulted in blindness or lead poisoning  in those who consumed tainted liquor.  This was an issue during Prohibition when many died from ingesting unhealthy substances. Consumption of lead-tainted moonshine is a serious risk factor for saturnine gout, a very painful but treatable medical condition that damages the kidneys and joints. 
Although methanol is not produced in toxic amounts by fermentation of sugars from grain starches,  contamination is still possible by unscrupulous distillers using cheap methanol to increase the apparent strength of the product. Moonshine can be made both more palatable and perhaps less dangerous by discarding the "foreshot" – the first few ounces of alcohol that drip from the condenser. Because methanol vaporizes at a lower temperature than ethanol it is commonly believed that the foreshot contains most of the methanol, if any, from the mash. However, research shows this is not the case, and methanol is present until the very end of the distillation run. Despite this, distillers will usually collect the foreshots until the temperature of the still reaches 80 degrees celsius.  Additionally, the head that comes immediately after the foreshot typically contains small amounts of other undesirable compounds, such as acetone and various aldehydes. 
Alcohol concentrations at higher strengths (the GHS identifies concentrations above 24% ABV as dangerous ) are flammable and therefore dangerous to handle. This is especially true during the distilling process when vaporized alcohol may accumulate in the air to dangerous concentrations if adequate ventilation is not provided.
A quick estimate of the alcoholic strength, or proof, of the distillate (the ratio of alcohol to water) is often achieved by shaking a clear container of the distillate. Large bubbles with a short duration indicate a higher alcohol content, while smaller bubbles that disappear more slowly indicate lower alcohol content. 
A more reliable method is to use an alcoholmeter or hydrometer. A hydrometer is used during and after the fermentation process to determine the potential alcohol percent of the moonshine, whereas an alcoholmeter is used after the product has been distilled to determine the volume percent or proof. 
A common folk test for the quality of moonshine was to pour a small quantity of it into a spoon and set it on fire. The theory was that a safe distillate burns with a blue flame, but a tainted distillate burns with a yellow flame. Practitioners of this simple test also held that if a radiator coil had been used as a condenser, then there would be lead in the distillate, which would give a reddish flame. This led to the mnemonic, "Lead burns red and makes you dead." or "Red means dead." 
Varieties of moonshine are produced throughout the world.
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