In Japan the word sake is actually a generic term meaning alcohol and you’re better off sticking to the word nihonshu if you’re ordering the rice based tipple in the land of the rising sun. Outside of Japan you can use whatever you want and the term sake is not going anywhere anytime soon so I will stick to this usage.
Sake is a fermented alcoholic beverage like beer and wine with an average alcohol content of 15% to 17% with some reaching as high as 20% or 21%. Not to be confused with the other Japanese alcoholic beverage, Shochu, a distilled beverage like whiskey, gin and vodka. Steeped in history, the brewing process of sake has remained largely unchanged for centuries and is made from steamed rice, koji-kin (koji mould, scientifically known as Aspergillus orzae and regularly used in asian cuisine), water and yeast (a micro-organism that metabolizes starch-derived sugars into ethanol (alcohol) heat and carbon dioxide).
You’ll often hear the word ‘rice wine’ being thrown around since it has a similar alcohol level but sake is in fact made in breweries not wineries and closer to beer in its process. With wine, fermentable sugars are already present in the grape so it is simply a one step process of converting sugar to alcohol with the aid of yeast. Rice on the other hand has sugars present but in a different form, starch, which is actually just glucose bound tightly together. This is where Koji mould comes to the rescue and converts the starch to sugar for the first step and then yeast converts the sugar to alcohol. There is a slight difference when comparing beer and sake. With beer the conversion of starch to sugar and sugar to alcohol occurs in two separate steps whereas with sake the conversions occurs simultaneously, something known as multiple parallel fermentation.
Sake is most often clear and colourless but it is naturally yellow before the optional charcoal fining which removes the colour and arguably the goodness. Ones that are not charcoal filtered are referred to as Muroka 無濾過 and tend to have a little more character. Sake can develop even much darker colours (gold, amber and brown) with time and if stored at room temperature. It has a subtle aroma ranging from fruity and floral to savoury with lactic and cereal notes. Sake has around one third the acidity of wine with more lactic than tart acidity present. It’s delicate in flavour with minimal astringency but regularly abundant in the elusive fifth flavour, umami, making it easy to pair food with. Fish and shellfish such as oysters is a perfect match where it mutes the fishiness.