It’s a common debate and there are indeed some basic distinctions. Beer is any alcoholic beverage primarily made from grain, hops, water and yeast. Grain is heated in water to release sugar then hops are added to lend a complex flavour and bitterness to contrast with the sugar. Yeast is then introduced to ferment the sugar, producing alcohol and CO2. Lager and ale are both types of beer, but they undergo differing fermentation.
Ale is fermented using yeast that rises and works best at warmer temperatures (15-24 degrees Celsius/59-75 degrees Fahrenheit). Lager uses yeast that sinks and prefers cooler temperatures (5-12 degrees Celsius/41-53 degrees Fahrenheit). As a result, lager takes longer to ferment than ale, plus the colder fermentation inhibits the production of esters – the compounds responsible for fruity aromas and flavours often found in ale.
Answered by Rik Sargent