Science explains why it's so hard to cook the perfect cup of rice

Cooking a cup of rice can often be a daunting task.

From worrying about whether it will stick to the bottom of the pan to making sure you get the right water-to-rice ratio, it's easy to opt out and go for instant rice or just give up and steer clear of the grain overall.

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We chatted with Dan Souza, the executive editor of Cook's Science at America's Test Kitchen and one of the authors of "The Science of Good Cooking." He told us that one of the biggest myths he's debunked in the kitchen is about the correct ratio of water to rice. 

Anyone who's tried to cook rice on a stove top knows that you typically put in two cups of water for every single cup of rice. A few minutes later, you ideally have a pot of perfectly cooked rice. But that's not always the case. So why is it that even when you put in the same ingredients, your rice seems to come out either perfectly or completely ruined?

The experiment

To see if he and his team could find a better way, Souza said they put sealed bags filled with a cup of water and a cup of rice into boiling water. He found that regardless of what kind of rice was being tested — long grain, brown, white, etc. — it always took just a single cup of water to perfectly cook a cup of rice.

Which means that the single biggest thing separating you from that perfect cup of cooked rice is chemistry. Evaporation, to be precise! And evaporation can be a tricky thing to predict. 

"Evaporation isn't a consistent thing, cook to cook, kitchen to kitchen," he explained. "If you have a pot with not a very good lid, you're going to get more evaporation. If it's really tight, you're going to get less evaporation."

Things get even more complicated if you try to double your recipe. Say you want to make two cups of rice, so you decide to use four cups of water. Souza said that's not necessarily the best approach if you're using the same size pot as you would with just the one cup of rice.

"If you have a ration of 1:2 and you double that to 2:4, you're saying you're going to get double evaporating because you doubled it and that's not true," he said. "If you're using the same pot with the same diameter lid and the same heat you're going to have the same amount of evaporation as you did the first time. so you end up with an extra cup of water in there."

How to succeed at cooking rice

Ideally, if there was a device that could limit evaporation entirely (rice cookers still let off steam, so they require more water), that would be the best way to get a cup of perfectly cooked rice.

But in the meantime, Souza said, the best way to optimize your ratio is through trial and error, based on pot size, humidity, and of course how many times you peel the lid off too early.