The Chemistry of Cooking a Perfect Egg

May 17, 2011 | By | COMMENTS

The Chemistry of Cooking a Perfect Egg 1
Cooking the perfect egg may sound like such a simple order, yet this task harbors a wealth of culinary import. Cooking the perfect egg, be it hard-cooked or coddled, is a bit of a culinary feather in one’s cap. However anyone who has taken advanced cooking classes or even gotten an online PhD in one of the sciences knows that the reasons for this are myriad and relate primarily to the egg’s chemistry.


There are a number of variables that affect cooking times for eggs. Among them are altitude, the protein bonding temperature, the bonding temperature of the yolk, the age of the eggs and even the size of the pot in which they are being cooked. Below is a detailed discussion of each of these variables, as described by and the executive editor of Serious Eats, J. Kenji Lopez-Alt, whose Food Lab blog uses science to dispel the myths and get to the heart of what works in food preparation.
– Age of the Eggs: Farm fresh eggs are for frying but not for cooking. The inner membrane of the egg sticks to the white, making them difficult to boil. However, this bond breaks down after a few days on the shelf, meaning that any eggs you buy at the supermarket are perfectly acceptable for cooking.
– Protein Bonding Temperature: This is particularly important for understanding the transformation of an egg white and avoiding the rubbery texture that often plagues hard-cooked eggs. Basically, between 30 and 140 degrees the white’s proteins unfurl. Above 140 degrees, these proteins begin to bond. At 155 degrees, these proteins are solidified though still moist, and at 180 degrees, the proteins are bonded firmly, giving the white an opaque, firm texture. Above 180 degrees, hydrogen sulfide is released, leading to that disgusting “rotten eggs” smell.
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– Egg Yolk Temperature: The egg yolk contains some protein but is primarily composed of fatty acids and cholesterol. As such, it responds differently to heat. Below 145 degrees, nothing happens. Therefore, an egg simmered at 140 degrees for 45 minutes will have a completely liquid center but a shape-retaining white. At 158 degrees they are totally firm but still bright orange. At 170 degrees, they turn pale yellow and start to crumble, and above this temperature, they turn chalky and release ferrous sulfide, which also produces that “rotten eggs” smell.
– Altitude: According to the scientists at the U.S. Department of Agriculture (USDA) , at above 2,000 feet, water boils at a lower temperature (208°F instead of 212°F). This means that it simmers at a lower temperature too. In order to properly cook eggs, expect to add a bit of additional time when cooking them to ensure they reach the desired internal consistency.
While cooking eggs is in many ways more of a science than an art, there is room for experimentation. Once you have mastered the basics of egg cookery, whether you prefer them coddled of hard-cooked, you can begin to experiment with water temperature, pan size and cooking times to create your variation of the perfect egg.

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