The liquid being distilled is a mixture of mainly water and alcohol, along with smaller amounts of other by-products of fermentation (called congeners), such as aldehydes and esters. Alcohol (ethanol) has a normal boiling point of 78.4 °C (173.12 °F), compared with pure water, which boils at 100 °C (212 °F). As alcohol has a lower boiling point, it is more volatile and evaporates at a higher rate than water. Hence the concentration of alcohol in the vapour phase above the liquid is higher than in the liquid itself.