Despite this, distillers will usually collect the foreshots until the temperature of the still reaches 80 degrees Celsius (176 Fahrenheit). 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. The incidence of impure moonshine has been documented to significantly increase the risk of renal disease among those who regularly consume it, primarily from increased lead content. Outbreaks of methanol poisoning have occurred when methanol is used to adulterate moonshine (bootleg liquor). 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." Moonshine historically referred to "clear, unaged whiskey", once made with barley in Scotland and Ireland or corn mash in the United States, though sugar became just as common in illicit liquor during the last century. The word originated in the British Isles as a result of excise laws, but only became meaningful in the United States after a tax passed during the Civil War outlawing non-registered stills. Illegal distilling accelerated during the Prohibition era (1920-1933) which mandated a total ban on alcohol production under the Eighteenth Amendment of the Constitution.