Why Your Rice Boils Over – Rice grains are coated with a surprising amount of starch for such tiny grains. These starches, when boiled in water, form large, soapy, angry bubbles that the steam pushes out of the pot. Rice requires a lot of liquid to cook thoroughly; you must keep the lid on to prevent liquid from evaporating too rapidly.
What should one do if rice is boiling?
This is how to fix the problem with bubbling – Apisit Hrpp/Shutterstock According to The Whole Portion, rinsing the rice grains thoroughly before cooking them is the most effective and dependable way to eliminate the bubbling problem. Some cooks may choose to let the rice soak for an extended period of time to loosen the starch, but the process can be accelerated. 
Why is my rice cooker’s rice bubbling?
When there is an excessive amount of starch on rice being cooked in a rice cooker, the boiling water begins to form large, soapy, foamy bubbles. These bubbles rise to the surface of the rice cooker, causing it to overflow.