Should you drink Japanese Sake hot or cold?
After a hard days' work, what tastes better than a cold can of beer? Or, after an intensive afternoon on the skating rink, how sweet does a glass of warm glühwein taste?
The temperature of a drink (as with food) is very important for the overall flavour. Japanese sake is no exception. The only thing that is exceptional is that you can enjoy different types at different temperatures, ranging from fridge-cold (5oC) to tongue-scorching (50oC) temperatures.
Heat it up, or keep it cold?
That depends on 3 factors: your own preference, the food you're having it with, and most importantly, the sake itself. Some (or rather: most) sakes are brewed to be served at a particular temperature, and if you abide by that, you can ruin the flavor.
Traditionally, cold sake was known as good quality sake in Japan. Heating it up was a way of masking unwanted flavors. However, that is no longer the case (like it is no longer necessary for hygiene purposes to eat lemon and salt with your tequila shot, but that's a story for another time). Nowadays, sake that is served very cold (5oC) are usually pure sake (ginjō) of the fruitier, dryer kind. Warming up the sake in your mouth, the bouquet of flavors unfolds. Sake that is served cold (10oC) is likewise pure, but sweeter and rounder.
Room Temperature Sake
Not all sake has to be chilled or heated. There are some varieties (although a bit exceptional) that are best served at room temperature (15-20oC). Complex flavors have a chance to develop, so well-balanced sakes (including bottles of a few years old) are often served at this temperature. Note: if you don't finish the bottle, keep it in the fridge to preserve the flavor better.
Hot sake is probably the most well-known way to enjoy Japanese sake in the West. Basically, it depends on your own preference, but a large part of sakes can be enjoyed hot. The simpler varieties (called 'futsūshu' in Japan, or 'normal sake', sake with additives such as distilled alcohol) are best enjoyed hot (30-55oC). Heating up sake, especially up to 55oC is a tricky business, and you should be careful not to ruin the flavor, but it's best to just try out per variety how the flavor develops when heated up, and which flavor you prefer. Note that a variation of just 5oC can make quite a difference in flavor! Also, after a few cups of sake, be careful with the hot sake as you don't want to burn your tongue...