jazzfood wrote:that really came about after the war to appeal to american occupying forces during the winter.
This is not true. The tradition of warm sake (kanzake) predates American occupation, oh, a thousand years or so. Potted histories put warm sake as a noble beverage in the Heian era (from 800 or so), relatively widespread by Genroku (1688), and a very common national beverage by the Meiji period(1868). The sake was woodier and sweeter. It was brewed in wooden tanks, transported in wooden drums. It probably tasted like a sweet, boozy cedar trunk. You can still get wood aged sake (taru-zake), but it's now the exception rather than the rule. So, warmth was common to cover the roughness until brewing technology improved, stainless steel tanks, and glass bottles were adopted around 40 years ago.
There are also types that are usually served warm. For example, in the winter, a warm cup of a sweet, cloudy unpasteurized (namazake) sake. As you can imagine, people in ancient Japan turned to warm sake during cold winters. If you've been to Japan in the winter (or in the extreme heat of summer) you may have noticed that traditional achitecture doesn't do much with insulation ... hence all the layers or clothes. And warm sake.
As for masking flavors, it needs to be made clear that "warm" (nurukan) sometimes means hot (joukan). Steaming hot. 130 - 140. It's very unlikely you'll be served sake this warm at a restaurant; warm will usually be between 100 and 110. However, if you were, you'd notice that, as with most really hot beverages or foods, the aroma becomes a lot bigger but the flavor is greatly diminished. When we talk about cold (reishu) sake we usually mean cool (jouon). Over ice is a special case (yuk hie). As with white wine, ice cold means it tastes like nothing. Flavor is in the midrange temperatures (the afforementioned temperatures plus hitohadakan, or lukewarm).
Basically, sake has an incredibly wide range of serving temperatures - in common practice, wider than any other alcohol I can think of. Temperature depends upon many factors, from quality, to pairing, to season, to the consumer's preference. And, with that stereotypical flair for precision, every temperature and serving style is given a name, shooting the permutations rapidly into the stratosphere.
The history and process is pretty fascinating. I highly recommend the Sake World web site and newsletter:
http://www.sake-world.com/
rien