No need to heat the Sake
Sake can be a bit mysterious. Although the label lists the quality of the drink, it is in Japanese, so much of the description is cryptic for most of us. Sake's categories can be a bit confusing, but with a little bit of clarification understanding the different styles can make purchasing sake much easier. This comprehension will also help you appreciate what you are drinking.
      There are three different processes that factor into the sake classification system. These processes can overlap, but understanding each one allows you to grasp the naming system.
      The first thing that distinguishes each sake style is the amount of germ and bran milled away from the rice using a rice huller. This is called polishing. When rice is harvested it is milled to remove the chaff or hull, leaving behind brown rice. Further polishing removes the germ and bran. Polishing removes some of the proteins and fats that can impart off flavors in the sake. Proteins and fats can also inhibit fermentation. The more the rice is polished, the smoother the sake brewed from it will taste. Of course the more the rice is polished the smaller the grain becomes, which cuts into the profits.
      The second characteristic is whether or not brewers alcohol has been added to the sake. Inexpensive sakes add a significant amount of alcohol to the final product to cover imperfections. Adding alcohol can make the drink smooth. Better quality sakes will sometimes add a small amount of additional alcohol.
      The third characteristic is whether or not the sake has been pasteurized. Sake can be pasteurized to enhance shelf life. Non-pasteurized sakes are also unfiltered and must be kept refrigerated and drank soon. There are five quality designations for sake. Some of these styles can overlap.

1. Junmai-shu means there was no alcohol added to the sake.
2. Honjozo-shu has at least 30% of the rice's outer layer polished away. Honjozo-shu has some distilled alcohol added to the sake.
3. Ginjo-shu has at least 40% of the rice's outer layer polished away. If the sake is labeled Junmai-Ginjo it does not contain extra alcohol. If it is labeled Ginjo it has some distilled alcohol added to it.
4. Daiginjo-shu has at least 50% of the rice's outer layer polished away. If the sake is labeled Junmai-Daiginjo it does not have added alcohol. If it is labeled Daiginjo, it has some distilled alcohol added to it.
5. Nama-zake, which means 'cloudy sake' has not been pasteurized. Unfiltered sake is called nigori, but may be pasteurized. Nama-zake should be stored cold. All four of the above types of sake can be nama-zake.