The key to cooking Japanese rice nice and fluffy is
to circulate it in hot water when boiling in a pot.
In case of using a rice cooker of 20 cups,
you are recommended to put 12-13 cups of rice
instead of 20 cups to the maximum.
The room may prevent uneven cooking because rice
has enough space to circulate. On the other hand,
if you cook only 3-4 cups of rice with the rice cooker of 20 cups,
it may cook too quickly and leave a hard core at the center of the rice grain.
Choosing a rice cooker properly depending on the restaurant’s menu items
or the capacity is quite important.