according to sushifaq.com:
Hot Sake vs. Cold Sake
Historically, sake was served warm. The reasons were twofold. Firstly, this ancient drink was created before refrigeration and was therefore habitually served that way after methods to chill food and drink were developed. Secondly, sake was also historically a much more coarse beverage, and often took up flavors from the wooden casks in which it was stored. Many off flavors were also a side effect of the fermentation process, which were masked by serving the sake at a higher temperature. More recently, better brewing techniques, more refined strains of yeast and koji, and modern storage practices have created a very different product than in the past. A more refined product does not mean that all sake is the same, however. Just as western wines have subtle differences, so do sakes from different regions and different manufacturers. In general, high quality sake is meant to be consumed cold, while lower quality sake is drunk warm, which can hide off flavors that are created during the fermentation process of the cheaper brands. That said, the peak flavor higher quality sakes can be achieved at subtly different temperatures, different for each brand. To most people, this difference will not be noticeable (similar to the many different kinds of tea, each of which has an 'optimal' brewing temperature). But a general rule is that good sake should be served slightly chilled, but never too cold as many of the subtleties of the beverage may be muted when the drink is too cold. There are a few decent sakes, however, that are meant to be served slightly warmed, and will be labeled as such, and can make a nice treat on a cold winter day, but as a general rule, higher quality sake should be served slightly chilled.
generally speaking, premium sakes (junmai daiginjo/ daiginjo shu, junmai ginjo/ ginjo shu, junmai/ honjozo shu) should always be served at room temperature or slightly chilled (a la chardonnay).
