What role does the rice pot lid having no steam vent hole play?

When facing the rice pot, the first spot that catches the eye is the smooth top surface of the lid. There is no hole. The steam vent commonly found on typical pot lids is not provided at all on Oigen Foundry's rice pot^[1]. This rice pot, including the lid, is made entirely of cast iron^[2], and its total weight reaches 2.8kg^[3]. When the heavy cast iron lid presses down on the pot from above, steam cannot leak outside and is sealed inside. As pressure and moisture are trapped inside the pot, high temperatures are maintained evenly, transferring heat deep into the core of each rice grain.

However, the lack of a hole for steam to escape requires special attention to flame control. Because boiling steam cannot escape through a vent, the rice water can easily boil over through the gap of the lid even if the heat is only slightly strong^[4]. Generally, when using a cast iron rice pot, one must lower the heat immediately upon noticing signs of the rice water boiling up and let it steam gently under mild pressure.

hmmm, rather than having a safety hole that prevents boiling over, it is a method that guides you to stay by the flame and concentrate entirely on the cooking process.