The energy efficiency of the appliance will only be a small dent in the energy consumption of cooking the rice. Most methods rely on boiling the water. Heating water up doesn’t take very much energy - about 4 kJ/kg/K. This means that heating 1 liter of water from 20 C to 100 C takes about 320,000 Joules (1 kWh = 3,600,000 Joules).

Once water is heated up to 100 C, the next step is boiling where you phase change from liquid to vapor. The specific enthalpy of vaporization for water at atmospheric pressure is about 2000 kJ/kg, so the one Liter of water would take 2,000,000 Joules to completely vaporize. You could weigh your pot before and after cooking to see how much water you vaporized.

Let’s assume you have 1 kg (about 1 liter) of water and 1/10 of it vaporizes. The minimum energy for this is about 500,000 Joules assuming 100% efficiency. Divide by efficiency, so if the appliance is 90% efficient it would be around 550,000 Joules, while 80% would be about 625,000 Joules.

So, to answer your question, the most energy efficient method will minimize vaporization. Soaking the raw rice for a few hours will help reduce boiling time. Then use a standard issue rice cooker, which should stop the boiling process as soon as the rice is finished.

My guess is pressure-cooking, specifically with an instant pot (which is near BIFL).

Depending on how organised you are, and how much soup/boiled root veg you eat, soaking your rice over night and steaming it over soup/veg you’re boiling the next day, is going to be much more energy efficient than probably all other methods.

I think brown rice only takes about ten minutes to steam once it’s been soaked overnight, but I have never actually tried this method myself as I don’t eat that much soup or boiled root veg, and I have a bad habit of forgetting things if they’re not in my direct line of sight.

I cook all the rice I eat in an enamelled cast iron pot, on an induction stove hotplate.

(I am hella poor these days and have metered electricity, this has been the cheapest way I’ve found so far that works for me.)

• Add 1 part washed brown rice into the pot

• Add 1.5 parts cold water into the pot

• Add salt or stock cube/seasoning if desired

• Bring to a rolling boil for 2 to 3 minutes

• Cover pot with foil and lid to trap heat and steam

• Reduce heat to the lowest it can go while simmering continously

• Simmer for 15 minutes

• Turn off heat but do not touch or move the pot.

• Wait 15 to 20 minutes for the rice to steam cook the rest of the way.

This method works great, unless it is the dead of winter and cold enough in my kitchen that the pot cools too quickly to finish steaming the rice through. In which case I add a little more water and bring it to a boil again, and cover, lower the heat and steam it again for ten minutes, while hovering over the pot shivering and debating whether or not to just eat it as is, or wait for it to be both mushy and crunchy.

I don’t know about energy efficiency, but I’d imagine it’s pretty good, but a Japanese rice cooker is cheap and reliable with perfectly cooked rice every time.

I have a Philips but I know there are lots of Japanese brand rice cookers that are more reliable. It can also be used for steaming.

For lower budgets, stainless steel aroma rice cookers last a really long time. My parents have had the same aroma rice cooker for the past decade and use it everyday (more than once a day on avg). I would find it difficult to tell the difference between it and one that’s only a month old.

For higher budgets and higher efficiency (because they trap the steam and use the pressure), you can go for a premium japanesee brand like zojurishi or tiger.-

Yum Asia (Chinese brand) rice cookers are somewhere in between the premium Japanese ones and the low budget aromas.

While the rice cooker itself is fairly bifl for all these options, the inner pot is not.

Aroma has stainless steel inner pots which are truly bifl. The east asian brands mostly have Teflon nonstick inner pots which aren’t bifl as the nonstick will start peeling after a few years and you will need to get a replacement inner pot. Tiger and Yum Asia also offer a ceramic inner pot which will last longer than the Teflon, but not as long as the stainless steel.

With aromas, you need to physically remove the pot once the rice cooker is done or the bottom of your rice will get a bit burnt if you leave it in keep warm mode for too long. The mid and premium end brands won’t burn your rice even if its on keep warm mode for hours.

Keep warm mode is what rice cookers go into once they finish cooking the rice and give you the rice cooking finished signal.

I’ve always understood rice cookers to be most energy efficient. If I had to guess why, it’s probably a factor of insulation and their precision of temperature control. Less heat is lost versus the stove top.

Admittedly, that’s mostly a hunch. But even if my opinion here is misinformed, the convenience factor of the rice cooker can’t really be overstated.

I don’t know if I have a BIFL recommendation. I got a mid-tier one to see if I liked it and would use it, and usually when buying my first appliance of a new kind longevity isn’t my biggest concern. But now I know I won’t go back to making rice on the stove top, so for my next one I’d hope to buy it for life.

Mine is an Arrow Professional Plus. I’ve had it close to five years now and it still looks and behaves as new. I might have already stumbled into buy-it-for-life, I don’t know

I guess you want unattended cooking. But if that’s not the case, and you’re doing other stuff in the kitchen, an induction cooktop is the most versatile option. Some even let you set a temperature so you’re not wasting energy.

Probably this https://www.amazon.com/Zojirushi-NP-HCC10XH-Induction-Heating-Stainless/dp/B00VAG84O2

If you’re cooking by electricity, it’s all roughly the same. It’s all running close to as efficient as it possibly can be. In theory, some kind of heat pump could do better, but that’s not really viable for this use case. It’s hard to make them both compact and provide enough heat for cooking.

If you’re cooking in a pot on a stove, an induction stove top will do better. As far as dedicated rice cookers go, though, they’re all the same. Might be more efficient than any stove top because they lose less heat to the surrounding area during use.

I have no idea, I usually use a slow cooker.