Sloppily-produced moonshine can be contaminated with toxins, mainly from materials used in construction of the still. Despite the well-known hazards, it is claimed that stills constructed using car radiators for a condenser are still used. The lead used in soldering these radiators ends up in the moonshine, and in some cases, glycol products from antifreeze used in the radiator can appear as well. Both are poisonous.
Occasionally moonshine is deliberately mixed with industrial alcohol-containing products, including methanol and denatured alcohol. Results are toxic, with methanol easily capable of causing blindness and death. This resulted in moonshine being known as white lightning, since anyone drinking this mixture would literally be 'struck blind'.
In the past moonshine has been mixed with soap, to fool people into believing that it is of a higher proof.
Methanol and other toxic alcohols can occur naturally in distilled spirits and are called fusel oils. The methanol is concentrated in the first few percent of condensate produced in a batch. The fusel oils are mostly found at the end of a batch or run. Ordinarily these portions are discarded, though if ingested alone or included with the rest of the distilled product it may cause toxic effects. Like commercial beer, wine, and liquor, properly produced moonshine contains small amounts of methanol at levels that are not toxic. A common way to determine the "quality control" of a batch of moonshine was to see if the moonshiner would dare to drink it.
A common quality test for moonshine was to pour a small quantity of it into a metal spoon and set it alight. Safe distillate burns with a blue flame, but tainted distillate burns with a yellow flame. If a radiator coil had been used as a condenser there would be lead in the alcohol, which would give a reddish flame. This lead to the phrase: "Lead burns red and makes you dead." Of course, these tests should not be solely relied upon to test the purity of moonshine or any distilled alcohol.
In addition, moonshine that is over 100 proof (i.e. 50%) is very flammable and easily ignitable. This is especially true during the distilling process in which oxidized vaporized alcohol can accumulate in the air if there is not enough ventilation.
Iron poisoning can sometimes result from uncoated iron tubs in which the mash has been boiled.