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Nowadays, premium sake is usually served chilled instead of warm. However, if you have a less expensive type or homemade sake, or simply want to draw out a different dimension of flavor, you can try heating it before serving it. This can be an especially good option for a cold winter day.  Heat causes the alcohol to vaporize. Aroma-producing ingredients with low boiling points also vaporize, making these flavors stand out more. This has very little effect on bitter acidic tastes, but sweet tastes get pronounced more effectively. As such, sake with a high level of acidity is often heated since the process can balance the acidic flavor with the sweet undertones more evenly.  Warm sake also tends to have a "dry" taste when compared to chilled sake. The effect of the alcohol is increased as the vapors begin coming off. There is a full range of temperatures you can heat sake to, from lukewarm to hot. The right temperature to use depends partially on personal preference, but there are a few standard approaches to take that you might want to consider.  The average temperature of kan sake, or "warm sake," is between 107.6 and 113 degrees Fahrenheit (42 and 45 degrees Celsius). The full range of possible warmth varies slightly beyond this, though, and each range of warmth has its own traditional term associated with it. At 86 degrees Fahrenheit (30 degrees Celsius), sake is referred to hinata-kan, or "warmed in the sunshine." At 95 degrees Fahrenheit (35 degrees Celsius), sake is referred to as hitohada-kan, or "heated to body temperature." At 104 degrees Fahrenheit (40 degrees Celsius), sake is referred to as nuru-kan, or "heated to tepid temperature." At 113 degrees Fahrenheit (45 degrees Celsius), sake is referred to as jo-kan, or "heated fairly warm." At 122 degrees Fahrenheit (50 degrees Celsius), sake is referred to as atsu-kan, or "heated hot."   As a general rule, warm sake is ideal as an accompaniment for cold or plain dishes, like sushi, as well as dishes that have soy sauce in them. Hot sake, on the other hand, is ideal to serve alongside warmer dishes, like hot pot, or foods made with a large amount of oil or fat.  Two types of sake that are often heated include junmai and honjozo. Junmai sake is often served fairly warm to hot.Honjozo sake is typically served warm at room to body temperature.

Summary:
Know when to heat sake. Determine the right temperature.