Equipment Science: How rice cookers cook dinner rice with out burning

One of many nice issues about know-how is the way it frees folks from mundane duties. Cooking rice is one among these. In case you have ever cooked rice manually, you will know what a trouble it may be. You must preserve a detailed eye on it: get distracted and it’ll boil dry, burning the rice on the backside and ruining the remainder. Fortuitously, you do not have to fret about this in most trendy kitchens, as a result of an affordable gadget referred to as an automated rice cooker handles this for us, turning down the warmth when the rice is completed to maintain it heat with out burning. How does it do that?

The brief reply is by taking note of the temperature. The lengthy reply is by taking note of the temperature in a fuzzy, informal type of manner. I will have a look at the brief reply on this column, and the lengthy reply within the subsequent one.

The earliest automated house rice cookers got here out within the late 1950s from firms like Toshiba. Business fashions had been round for some time earlier than this, utilizing a wide range of methods to measure the doneness of the rice, however the first house fashions relied on the truth that water conducts warmth higher than rice does, and that it boils at 100℃ (212℉) at sea degree.

The Oster 20, a easy, low-cost rice cooker


Oster

While you use a rice cooker, you set water and rice (often in a 2:1 proportion) right into a steel bowl, which has a heating component and a temperature sensor beneath it. These are often on springs to press them towards the underside of the cooking bowl to verify they will conduct the warmth nicely. The bowl is skinny and manufactured from a steel like aluminum that conducts electrical energy nicely.

When the automated rice cooker is turned on, the heater begins heating the bowl, which conducts the warmth into the water and the rice. As a result of this combine is principally water at this level, it heats up till it begins to boil. As soon as it begins boiling, the warmth is carried off within the steam that rises from the bowl. So, the temperature of the dish on the backside of the bowl will not go a lot larger than 100℃ (212℉), as a result of the water on the backside of the bowl will boil, flip to steam and carry off the warmth.

In the meantime, the rice is cooking, absorbing the water into its construction, which is principally composed of starch. Starch is usually composed of lengthy strings of sugar molecules tied collectively, with just a few different chemical compounds thrown in. When they’re heated, these lengthy sugar strings seize onto passing water molecules in a course of referred to as hydrogen bonding: the hydrogen within the water weakly bonds to the oxygen atoms which can be poking out of the perimeters of this chain.  Due to this, the rice grains soak up the water, and change into much less nicely related to one another, a course of referred to as gelatinization. In case you saved including water, this may finally flip right into a gooey paste. Nonetheless, you do not need that to occur (until you make rice pudding or porridge) which is why you solely add a certain quantity of water: sufficient for the rice to soak up and swell, however not sufficient to interrupt the construction down utterly.

When the rice has absorbed all of the water, the heater continues to be pumping warmth into the bowl together with the rice, but it surely would not have any free water left to take away it by boiling, so the temperature of the bowl shortly rises.

That sudden temperature bump triggers the mechanism contained in the rice cooker to show the warmth down or off, as a result of the rice is completed. The primary rice cookers (and lots of low-cost fashions in the present day) used a bimetallic swap, the place two metals increase at totally different charges when heated, triggering at simply over 100℃ and releasing a latch, producing the acquainted “clunk” that permits you to know the rice is completed.

That is the brief model. The lengthy model has to contemplate a pair extra points: water boils at decrease temperatures at altitude, and the easy swap solely permits you to have one set off for doneness: you’ll be able to’t modify it for various kinds of rice that will soak up totally different portions of water, or for various makes use of comparable to making porridge. Automated rice cookers that may deal with these use a dfferent strategy, referred to as fuzzy logic. We’ll talk about this in my subsequent column. 

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