Saké should be kept in a cool place out of direct sunlight, best in the cellar or in the fridge, and normally consumed within a year of being bottled unless its Namazake, unpasteurised Saké, or Aged Saké. In case of Namazake, one should drink it up within 1 to 4 months, which depends on the brands so please consult VINOWA for consuming recommendation.
If the Saké is well made, meaning each preparation and brewing process was completed well, Saké can be aged to produce richer & deeper taste profile, often matured to taste like port wine or giving chest nutty flavor.
TIP 1: Saké that is warmed should never be too hot, but rather just above body temperature, about 100-104 degrees Fahrenheit (40 to 45 degrees Celsius). When you warm up Saké, the best way is to place a filled flask (tokkuri) in the sauce pan or pot of hot water, allow it to slowly warm up rather than placing a filled flask in the microwave.
However, if you are too tired or feel lazy to proceed it in steps and want to resort to the modern technology, then cover the flask well down below the neck(normally towards the top of flask, there is a dip called "kubi" meaning neck in Japanese, where you can hold the flask with) with aluminum-foil before placing it in the microwave, this helps the bottom of the flask warms up first creating circulation within to warm up the entire Saké.
TIP 2: Well brewed Saké can be enjoyed at any temperature however one should try the same type of Saké at different temperature and in style (mixed with ice, water, hot water, etc) to find out what works best for a given Saké and also to match your taste. An excellent way to find what's best is to slowly warm up a chilled Saké into room temperature up to 45 degrees, then allow it to cool down to room temperature again*(called *"kan-zamashi"), tasting it all the while.
Pouring Saké for others is a common custom in Japan. Small cups (called ochoko or guinomi) and a larger serving flask (tokkuri) allow for frequent refill opportunities, each of which is a mini-ritual of social bonding. In formal situations, the tokkuri is held with two hands when pouring. Likewise, the person receiving should lift his or her glass off the table, holding it with one hand and supporting it with the other. Among close friends, all these pouring rituals are often abandoned for convenience. Pouring for yourself is known as "tejaku" in Japanese.
Your companions may feel compelling urge to refill your cup when it is empty. Rather than resisting their offer, the best approach is to allow your cup to be filled and then take tiny, tiny sips each time so that it never goes dry.