Low power pilaf: energy and rice cooking

Unloading rice - from IRRI Images at flickrAs I was doing research on energy use in rice production and transport, I ran across some interesting academic papers in the food science literature. I hope to be able to summarize some of them in the future, starting today with "Energy conservation in domestic rice cooking", an article in the Journal of Food Engineering by several researchers from India (full citation below).

The researchers cooked white rice using 22 different methods and measured the energy input required for each method. Here’s a quick summary of the results:

  • The electric rice cooker required the lowest energy input–two or three times less than the other methods
  • A pressure cooker will reduce energy consumption by about 50 percent compared to an atmospheric cooker
  • Presoaking the rice for 30 minutes can reduce the energy needed by between 7 and 18 percent

After the jump, I’ll describe the paper’s results in more detail.

The researchers’ created a test matrix of twenty-two different rice cooking tests by combining these independent variables:

  • Three methods: electric rice cooker, a pressure cooker without the pressure cap in place ("open cooking"), and a pressure cooker with the cap in place
  • Two soaking states: unsoaked or presoaked for 30 minutes
  • Three ways of heating the rice: cooking at high power for the whole period, starting at high and switching to low, and using "controlled cooking" (apply heat until the temperature reaches 100 C, turn off the heat until the temperature drops to 90 C, repeat until the rice is cooked) .

I pulled out the most interesting items from the data tables and have presented them in two plots below. The first one shows the relative energy consumption of several methods, and the second shows the effect of presoaking on energy consumption.

The figure below shows the relative energy consumption for different cooking methods using unsoaked rice (in this plot, shorter bars are "better"). The method and energy sources are abbreviated in the figure as follows: ERC for electric rice cooker; O for pressure cooker without the cap ("open cooking"); PC for a pressure cooker with the cap in place; E for electric stove; and G for gas stove. One of the results if from a "high-low" open cooking experiment on a gas stove–denoted as "O-G-HL"–in which the water was brought to a boil over high heat and then the heat was reduced to low for the remainder of the cooking period.

In this experiment, the electric rice cooker was by far the most efficient device, using two to three times less energy than the other methods. Using the pressure cooker gave a significant energy benefit on both the electric and gas stoves. A pressure cooker speeds up cooking by increasing the boiling point of water (typically to about 257 F (120 C). Wikipedia has more details.). The advantage of the rice cooker assumes that the rice will be eaten immediately, not allowed to sit in the "keep warm mode" for hours.

Relative energy in rice cooking


For me, one of the most interesting results in the study was the effect of presoaking on energy consumption. Presoaking rice speeds cooking by equilibrating the moisture content before the heat is turned on. A presoak also helps cooking by causing fissures to form in the grains, thus allowing water to be absorbed more quickly.

But how long should you soak the rice? The authors of the paper found an answer through careful measurement of the moisture levels of rice samples after different soaking durations. "Dry" rice had 12.5 percent moisture. After adding it to cool water, the moisture level rose rapidly, reaching 26 percent in one-half hour, and then leveling off at about 27 percent for the next four and one-half hours. Thirty minutes, they concluded, was good enough.

The plot below shows how presoaking reduced the energy consumption for each cooking mode (longer bars show more influence of presoaking). Presoaking reduced energy use by between 5 and 18 percent for the all methods except the pressure cooker over the gas flame (no explanation was given for the PC-G result).

Energy savings by rice soaking


In the interest of brevity, I left out the researchers’ results for the controlled cooking experiments–the experiments where they adjusted the heat input throughout the cooking process (something that would be relatively easy in an electric rice cooker). They are quite interesting, however, so I’ll try to write about them and some larger issues in the future.

Next time you cook some rice, try presoaking your rice to save a bit of energy. If you eat a lot of rice, look into getting an electric cooker or pressure cooker (which also cooks most beans and grains with less energy input).


Reference: Energy conservation in domestic rice cooking, by Tribeni Das, R. Subramanian, A. Chakkaravarthi, Vasudeva Singh, S.Z. Ali, P.K. Bordoloi, Journal of Food Engineering 75 (2006) 156–166.

Photo from IRRI Images flickr collection, subject to a Creative Commons License.

6 Responsesto “Low power pilaf: energy and rice cooking”

  1. babaco says:

    thanks! this was really interesting.

  2. Sam Fromartz says:

    Was kind of rice was it? Brown has more fiber but takes longer to cook, so you have to weigh your health benefits against your energy conservation goals.

  3. Rice variety: The rice variety was in an earlier draft, but somehow it dropped out in the editing process. The authors used “milled B.T. (Bangara Thigadu) variety rice.” I tried to find more about this “Bangara Thigadu” variety, but neither Google nor Ask nor Dogpile find any webpages containing “Bangara Thigadu” beyond the paper discussed above (a recursive search of sorts).

    Brown vs. white: The question of energy use in brown rice vs. white rice was not addressed in this study. Properly making the comparison also requires examination of the energy required to mill the rice (a figure I think I have seen somewhere, but can’t remember where).

    Brown vs. brown: I have a hunch that the relative energy consumption of different methods will be similar for brown rice, so if you are a brown rice devotee, presoaking or an electric rice cooker will probably allow you to reduce the energy required to cook the grain.

  4. Grains are the easiest things to cook in a solar cooker–a total no brainer. Rice never gets scalded the way it can on the stovetop…
    Every day I cook rice for our dogs using our solar oven. I just put the pan in the oven when I leave for work and it’s done when I get home. ZERO energy, just a little thinking ahead.
    Solar cookers are really amazing… I recommend the Sport Solar Cooker (got mine from the folks at Path to Freedom)

  5. Queen Whackamole –

    Funny you should mention cooking rice in a solar cooker…yesterday I tried to use my solar oven to cook (or to sun?) a pot of rice and a pot of lentils. My cooker is a home-made cardboard box and aluminum foil type, which I will post about here next week. It was my first attempt at “remote solar cooking,” in which I set it out on the back deck before going to work, aimed it to get sun from 2 PM onwards, and let it cook while I worked. However, when I came home in the evening, I found that the cover had fallen, making it a “no-lar” oven.

    I’m trying again today, with an Indian dal recipe that normally requires 5 hours of cooking at the lowest heat possible–but not boiling.

  6. Memo says:

    An excellent way of cooking rice very efficiently is to use a hay-box. Hay-boxes were originally  made from hay, but what I use is a Styrofoam box with blankets inside to insulate the pot. With that, you just need to bring the water to a boil, and then you can turn the stove off and put the pot in the hay-box. After an hour or two (depending on type of rice, soaking, etc.), the rice is ready. With this method, cooking rice does necessitate a little more preparation, but saves a lot of energy.