Cook rice in rice cooker takes about 30 minutes to 1 hour for most electric rice cookers to complete cooking. Some advanced models can back-calculate the cooking start time from given finish time. The time required for cooking rice depends on the amount of rice, the power of the heating elements, and atmospheric pressure, thus it is not constant. Pressure-cooker models are not influenced by atmospheric pressure. The special features distinguish high-end models from lower-cost, simpler models.
Rice is cooked by heating in boiling water or steam, or a combination (boiling until water evaporates, then continuing in steam generated by continued heating). It absorbs a great deal of water in the process, expanding its volume and using up the cooking water. The moisture and heat gelatinize and soften the starch granules in the rice. The cooking time for raw rice (not parboiled beforehand) ranges from about 15 minutes and up, depending upon the type and freshness of rice, method, and desired result (from separate grains to disintegrated porridge).
Commercial models can cook 20 or more cups. As a possible source of confusion, model specifications and names may list either cooked or uncooked capacity. Rice roughly doubles in size during cooking; therefore, a 10 cup (uncooked) rice cooker can produce up to 20 cups of cooked rice. The prices vary greatly, depending on the capacity, features, materials used, and the country of origin.
These inventions include, e.g., microprocessor-controlled cooking cycles, employing pressure cooking, utilizing induction heating (IH) that can generate heat directly within the inner cooking bowl itself (all the IH-type models are microprocessor-controlled), employing a varying pressure control mechanism (named the "dual-pressure" method) that creates repeated pressure/release cycles during the cooking, using various materials (e.g., copper, pure carbon, ceramic, diamond powder coating) for the inner cooking bowl because of their higher heat conductivity, utilizing more than one induction heating element, or employing a mechanism to collect and return the boiled over liquid to the inner rice bowl. The rice cookers which are very large to store tons of rice are used in places like Guruvayur.[clarification needed]
The pressure-cooking models can raise the water's boiling point higher, e.g., from 100 °C at 1.0 atm up to about 110 °C at 1.4 atm, which speeds cooking. They are also suitable for cooking brown rice (which contains oils and bran fiber that cook differently from pure white rice starch). The pressure-cooking models can also be used in high altitude areas.