Sometimes, the consumption of local made alcoholic beverages may cause

Sometimes, the consumption of local made alcoholic beverages may cause blindness or even death. This may be because of contamination of the beverages with :

Vinegar
Carbolic acid
Methyl alcohol
Formic acid
This question was previously asked in
UPSC CAPF – 2009
Blindness or death from consuming local made alcoholic beverages may be because of contamination with Methyl alcohol.
Ethanol (ethyl alcohol) is the alcohol intended for consumption in alcoholic beverages. Methanol (methyl alcohol) is a highly toxic substance that can be produced as a byproduct during improper fermentation or distillation, or sometimes illegally added to beverages. When ingested, methanol is metabolized by the body into formaldehyde and formic acid, which are potent toxins that damage the optic nerve (leading to blindness) and other organs, often resulting in death.
Vinegar is primarily acetic acid, which is relatively harmless in small quantities. Carbolic acid is phenol, a highly corrosive and toxic chemical. Formic acid is one of the toxic metabolites of methanol, but the primary contamination is usually with methanol itself.