By cooking rice in a specific way, starches and sugars in the rice react differently which gives the rice an extra tasty or 'umami' taste.
Yumami or ‘extra tasty’ rice function on Bamboo enhances the flavour of any type of white rice by using a specially designed cooking cycle, It does this by using a sequence of soaking and steaming to release the sugars contained in the rice that are then reabsorbed back into the rice as a different chemical structure that can activate Umami receptors of the tongue which results in extremely flavourful rice with improved texture/taste.
The full cooking time, including the special soaking and steaming, for the Yumami function on Bamboo is 1 hour, 6 minutes.
Zojirushi models NS-YSQ10/18 also has a ‘premium’ taste function which is similar to Yumami and the full cooking time, including the special soaking and steaming, takes around 1 hour and 15 mintues.
Umami, the 5th dimension of flavour
Umami is know as the 5th dimension of flavour, is also referred to as savouriness and is said to be the fifth taste after sweetness, sourness, saltiness, and bitterness. The ‘Yumami’ or ‘Premium Taste’ menu setting soaks and steams the rice longer for enhanced depth of flavour.
The following chart explains the process in more detail