Sake and yeast
Sake has a very complicated relationship with yeast, You could say it is the determiner to a large degree of the flavour. Here is a great article about the different types of yeasts, mostly described by their number, and what effect they have.
One of the most famous sakes determined by yeast is Masumi and their use of yeast number 7.
Enjoy the article. And remember if you want to buy sake in Australia here is the place!