Different drinks tend to use difference sources for their starch - whisky uses barley, wheat or rye and these can impart a characteristic taste to the drink. Other sources of starch can be used e.g. potato, sweet potato and other vegetables though not often commercially - the brewer tends to use starch sources readily available in the part of the world they are working.
|Moromi, the main mash|
|Grain of rice on which|
koji is propagating
One effect of this 'co-culture' technique is that the yeast continues to work for longer, producing more alcohol and a stronger drunk compared with western brews (beers 5-7%, wines 11-14%, sake 14 - 20% alcohol). Another is that the use of a 'pure' source of starch gives a distinctive flavour, and that flavour is contributed to by the particular strain of koji in use in each factory.
The use of Aspergillus to brew the beverage is more efficient, allows more starch to be turned into alcohol and gives the drink a distinctive taste!
An introduction to Sake (Esquire)