Blissfully Boiled Eggs
Boiling eggs may sound like the simplest thing you could possibly cook, but if you’ve ever boiled an egg you’ve probably run into problems at one time or another. The challenges with boiling an egg generally fall into two categories: cooking the egg, and peeling the egg. Despite following a set of directions precisely you might have found your eggs under/over cooked, or perhaps when you tried to peel the egg it ended up looking like the surface of the moon.
The good news, is that both of these problems are easily resolved with a little understanding behind the science of eggs. Read on and you’ll be boiling perfect oval eggs whether you prefer them hard-boiled or soft in the center.
The first thing you have to understand is that the egg yolk sets at a much lower temperature than the egg white (70 degrees C vs 80 degrees C). Since the heat source (boiling water) is outside the egg, the egg cooks from the outside in. In theory this means that by the time yolk is set, the white has also reached it’s higher setting temperature.
The problem is that since the boiling water is significantly hotter than the setting temperature of the egg, it’s very easy to zoom past the desired temperature. Because the temperature is rising so fast, it’s difficult to pinpoint exactly when to stop the cooking to get the egg exactly how you like it. The problem with most boiled egg instructions is that they create a formula (put eggs in cold water, bring to boil, boil for X minutes) assuming you put the exact same size and temperature of egg into the same amount of water in a the same pan on the same stove… Well you get the idea.
But you can get a much better control over the cooking just by adopting a different approach.
Put refrigerated eggs in a heavy bottomed pot and cover with cold tap water so they’re covered by about 1″ (2.5cm) of water. Bring the water to a full boil (100 degrees C) over high heat, and then remove the pot from the heat. Let the eggs cook the rest of the way using the residual heat in the water. As the temperature of the egg rises, the temperature of the water will fall, which will give you a much wider window when your egg is perfectly cooked.
For how long though? Well, there a number of factors that need to be taken into consideration, but let’s assume large eggs, out of the fridge, being cooked at sea level (or at least, not at the top of a mountain), 4 eggs to a suitable pot.
2 minutes – The white isn’t fully set and the yolk is totally raw
4 minutes – The white is fully set, but the yolk is thick and runny
6 minutes – The white is fully set, and the yolk is mostly set, but still a little runny in the middle
8 minutes – The white is fully set, and the yolk is set, but tender
10 minutes – The white is fully set, and the yolk is fully set
Remember to transfer your eggs to cold water as soon as you take them out of the pot to stop the cooking immediately. Otherwise, your eggs will continue cooking even after you’ve taken them out of the water.
Blissfully Boiled Eggs
- Place the eggs in a small to medium size pot, and add enough water to submerge the eggs about 1" under
- Bring the water to a boil then remove the pot from the heat (If you have a little time, this is the best way to get perfect boiled eggs. As the water will keep cooking the eggs, but slower, once you take it off the heat, you have more of a window to get the timing right.)
- Start the timer - 4 minutes for runny yolks, 6 minutes for yolks just stating to set
How to peel an egg
The good news is, after some experimentation, I’ve come up with a method that works every time, no matter how fresh the egg is. The secret is to put a small crack in the bottom of the egg BEFORE you boil it. The crack needs to extend all the way through the hard shell, but it must not rupture the membrane (otherwise you’ll end up with egg white spewing out of the crack as it boils). I use a small curved object (the end of a wooden pestle) to crack the egg on, because it creates a more predictable circular crack rather than a linear crack that could spread and rupture the membrane.
So why does this work? To understand this, it would help to understand why older eggs are easier to peel than fresh eggs. Unfortunately there is no scientific consensus on why an aged egg is easier to peel than a fresh egg. One thing we do know is that the albumen in a fresh egg contains more carbon dioxide, which means it has a lower pH (more acidic). This leads to one popular theory: that the acidity somehow makes the albumen adhere to the membrane more than an older egg with a higher pH.
As an egg ages, the moisture in the albumen seeps through the membrane and evaporates through small pores in the shell. This is what makes the air pocket inside an egg, and why it grows larger as the egg ages. Here’s where another theory comes into play: that the larger air pocket somehow makes the albumen adhere less to the membrane.
Personally I don’t buy either one of these theories because they don’t fit with my observations. While I don’t have any evidence to prove this (beyond my personal observations), my theory is that the higher moisture content in the membrane of an older egg prevents albumen from sticking to the membrane, making it easier to peel.
Peeling an egg
By putting a small crack in the shell, it allows water to enter the egg and saturate the membrane, mimicking the membrane of an older egg. If any scientists out there want to compare some cross sections of the albumen-membrane interface under a scanning electron microscope it would be awesome to finally put this mystery to rest.
Update: For very fresh eggs, you might find that the bottom of the egg (where the crack is) is easy to peel but the top is still problematic. For these eggs, just crack them all over using a blunt object such as the back of a spoon after they are boiled, and then soak them in cold water for 30 minutes. This should make the shell practically fall off.