See how to apply physics in the kitchen to make eggs with barely-set egg whites and still-runny yolks. The perfect upgrade for rice bowls, noodles and salads.

Time: 1/5
Well, I mean, technically it takes time to boil water

Effort: 1/5
Not much more than putting eggs in a pot and taking them back out

Thinking about heat

Legend has it that the Japanese would cook their eggs by leaving them in hot springs. The result is an egg that has been poached in its own shell, in water that never boils. With barely-solid egg whites and a still runny yolk, onsen tamago (quite literally, hot spring eggs) straddle the line between side dish, garnish and sauce.

Onsen tamago is a very useful addition to your skill repertoire. It’s surprisingly easy to make, and you can always make a big batch and keep it in the fridge for whenever you want to upgrade rice bowls (like Gyudon or Pork Bulgolgi bowls), noodles or salads with its silky, rich texture. Use it as a dip for breadsticks or a topping for toast. Or, it can be served on its own with a dash of soy sauce and a sprinkle of scallions as a snack. Think of it as a readily available, instant upgrade for any savoury meal.

In order to master the process, however, we must understand some theory. Like my middle school science teacher would say, there’s loads of good physics in this!

Egg whites coagulate at a lower temperature (60C / 140F) than egg yolks (65C / 145F) for complicated science reasons. If the temperature of the egg exceeds 65C/145F for too long, the yolk would set and stop being runny. On the other hand, if it does not stay above 60C / 140F the whites will remain a liquid. Our mission, should we choose to accept it, is therefore to keep the egg between those two temperatures for long enough to set the whites without setting the yolk.

This means we can’t just chuck the eggs in when the water is boiling, because that’s way above the yolk coagulation temp. It’s also very difficult (and time consuming) to fiddle with the heat on the stove to keep the water in the target temperature zone. Fortunately, there is a work-around.

Temperature wizardry

You know for sure that, barring extremes of altitude, water boils at 100C/212F. You also know that the total heat energy in the whole set-up will remain constant, and distribute itself more or less evenly. Therefore, if you mix two volumes of water together, you can pretty reasonably guess the resulting temperature since there isn’t any energy lost in phase changes.

So, if you were to mix 3 parts of boiling water with 1 part of room temperature water, you’d end up with water around the 80C/175F range. That’s still a bit above the yolk coagulation temperature, but it’s close enough. Some of the heat will go into heating the shells, and the heat has to go through the egg whites to reach the yolks anyway. The set-up will also be losing heat to the environment as time goes by as well, so the temperature will come down gradually. If the heat loss is slow enough, the eggs will stay in the goldilocks zone for long enough for the whites to coagulate.

Which is where this method comes from. Mix 3 parts boiling water with 1 part room temperature water in a pot, put the eggs in and cover. Let the eggs sit in the gradually cooling water, and it should experience the right amount of heat for the right amount of time as long as you use a sufficiently generous amount of water.

Of course, you could cook the eggs sous vide at a temperature somewhere in the goldilocks zone (say, 45 minutes at 63C/145F) and get foolproof results without expending any brain juice. I did not have a sous vide machine at the time of writing, but I picked one up second-hand later. It’s seen a ton of use, from good old chicken breasts, to fancy bone-in date night pork chops, to the most tender salmon you’ll ever taste!

So here I am, playing mad kitchen scientist. Thank you for nerding out with me today. Let’s make some eggs!

Dramatis Personae

Eggs – Yes

Here is where I’m supposed to tell you it’s better to use fresh eggs, or fancy brand-name eggs. To be honest, I’ve never really tasted a difference between basic and fancy eggs. (To be truly, truly honest, I’ve always been too cheap to get the fancy eggs so I wouldn’t know the difference)

Water – is it even an ingredient?

Good old H2 and O. Available from a tap near you!

Executive summary

1. Boil 3 parts water. Mix in 1 part room temperature water and switch off the heat.
2. Put eggs in and cover. Take them out after 15 minutes.
3. Wow, are we done already? Keep in the fridge, take them out and crack over whatever you’re serving them with, whenever you’re ready.

Play by Play

Of course, you will be needing some eggs. I gave them a rinse, just in case there’s anything nasty on the shell.

Here is the trick that is essential to the process. You want water that is hot enough to partially cook the yolk, but not so hot that it is set firm. I filled the pan with 3 bowls’ worth of water, and had another bowl of water ready at hand. Switch off the heat once the water in the pan reaches a boil, and pour in the rest.

Leave your eggs in for about 15 minutes. Cover the pan to minimise heat loss, and let it steep. You may want to take them out earlier or leave them in later, to fine tune the texture or adjust for the size and number of your eggs. And the temperature of your room, I guess.

Once they’ve spent long enough in the hot water, fish them out and place them in cold water to cool down. You may use them as soon as they are cool enough to handle, or keep them in the fridge for later.

Ideas for application. Here an onsen tamago is cracked over Gyudon, a classic combination. Check out how that yolk is faintly visible under the barely-set white, glistening and quivering in anticipation of being busted. It will become one with the sauce once mixed into the rice, and give everything a rich, smooth texture.

Yet another idea. Crack an Onsen Tamago over a Bolognese rice bowl for some contrasting colours and textures. Yeah you heard me right: pasta sauce on rice is a super meal-prep friendly recipe!

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