The Perfect Egg
Imagine this, you sit down for breakfast and order some sort of ubiquitous poached egg on toast variation. You anxiously slice the soft egg with your fork expecting a flow of warm golden goodness, but nothing happens… The yolk has been overcooked, the white is rubbery, and there is a slight sulfur smell emanating from your general area. Everyone looks around to see where that awful smell is coming from. You would probably be a little upset, but achieving the perfect runny egg yolk is actually more difficult than it seems.
I’m sure you know by now that the egg is packed with protein. Good for building your muscles and stuff, man. But, did you know that not all egg proteins are the same, and therefore don’t behave equally with respect to heat and time. There are 119 different proteins in the yolk alone. And besides, eggs are weird; they are liquid at room temperature and become solid when heated, isn’t that like backwards? This happens when the proteins break down, or denature, when heated. Imagine water molecules in the egg are a bunch of ping-pong balls and the proteins are bundles of yarn dispersed in the balls, as the temperature rises and the proteins denature, they become unraveled and tangle up the balls. Eventually the water is forced from the egg as the proteins become more and more dense, a la dry gritty egg yolks. Egg proteins start to denature, coagulate, and form structure at temperatures as low as 56°C, all the way to the last protein that coagulates at 80°C.
So, why do you even care? Well controlling what proteins we allow to coagulate controls how the egg tastes, feels, and smells. That last protein to denature is responsible for the rubbery unwanted texture of the hard-boiled egg whites and dehydrated gritty yolks. Ergo, boiling water is way too hot to cook a tasty egg. A well-cooked egg is heated only to the temperature corresponding to the coagulation of proteins that our tongue desires; in other words, somewhere around the 60°C -75°C range.
Creating the perfect egg
Maintaining a constant temperature on your kitchen stove is actually pretty hard, and besides, the difference between a flowing yolk and solid yolk is just 1 degree. So how can you hold an egg at say 62°C until the yolk reaches thermal equilibrium? The Japanese would cook eggs in their local “Onsen” hot spring where temperatures would stay pretty constant.
Unfortunately, I don’t live in Japan. But in recent years with the new generation of chefs who strive for perfection, lab equipment is being incorporated more in professional and home kitchens. This means that there is weird and intimidating equipment that can circulate water at a precise temperature. These “immersion circulators” are now commonly used to cook food sous-vide, or in a constant temperature water bath. Chances are you’ve eaten something cooked from one of these machines.
Using an immersion circulator, I’ve set up a simple experiment with 6 eggs all cooked for 1 hour at different temperatures; as you can see, the texture of the yolk and white change noticeably from a difference of just 1°C per egg.
Some things to note: the 60°C and 61°C are drastically different, this is because the 60°C egg was cooked after pulling the eggs from the refrigerator (started at a lower temperature) where the 61°C (and all eggs after) was cooked from room temperature. The yolk is liquid until the 65°C egg where the texture is like soft play-doh, the 65°C egg white is also noticeably more watery looking, this is because a certain protein in the white starts to coagulate at 65°C which happened to cling to the thicker white section (in the other eggs I was able to separate this protein from the white).
But wait, 1 hour for your breakfast egg? Actually as long as you avoid the temperatures relating to the off-putting proteins you can cook an egg much faster and just as good. In fact I usually cook at 75°C for 13 min, which makes the white slightly more firm.
Try this amazing egg calculator to see the t/T ratio for your preferred egg texture, and give it a try. I don’t expect anyone to have an immersion circulator but as it turns out a small esky is actually pretty good at holding water at temperature for a few hours, just start about 2°C above your final goal.