The 63 degree egg is the proverbial “cherry on top” of the smashed avo toast. It’s a culinary delight that many desire, but few dare to attempt. The perceived complexity and the need for precision can be daunting. However, with a dash of physics, a sprinkle of software, and a pinch of patience, you can master the art of cooking a perfect 63 degree egg every time.

If you’ve been following my blog, you’re probably aware that we have two adorable silkies. For those who aren’t familiar, silkies are bantam chickens that lay eggs approximately half the size (and weight) of a standard supermarket egg. For instance, a silkie egg weighs around 34.2 grams, while a typical “large” store-bought egg weighs about 58 grams. The smaller size means less mass to heat, which affects the cooking time. A five-minute boil, perfect for a runny supermarket egg, would result in an overcooked silkie egg - a catastrophe in other words!

As a perfectionist with a penchant for problem-solving, I recognized this as a classic thermodynamics heat diffusion challenge. I was confident that I could find the necessary constants for the properties of an egg online. Once I had the required information, I eagerly set about writing a short code. To my delight, the results were spot on!

The code I developed is rooted in the principles of thermodynamics, specifically heat diffusion. It considers the size and weight of the egg, the initial temperature, and the desired final temperature. The code then calculates the precise time needed to cook the egg to a perfect 63 degrees.

import math

def calculate_cooking_time(egg_mass_g, init_egg_temp, altitude):
    K = 5.4 *1.0e-3 # thermal conductivity of egg
    PI = math.pi
    EGG_DENSITY_G_CM = 1.038
    EGG_HEAT_CAPACITY= 3.7
    yolk_temp_celsius = 63
    water_temp = 100 - 0.0065* altitude

    first_component = (egg_mass_g**(2/3)*EGG_HEAT_CAPACITY*(EGG_DENSITY_G_CM**(1/3))) / (K*(PI**2)*((4*PI/3)**(2/3)))
    second_component = math.log(0.76*((init_egg_temp-water_temp)/(yolk_temp_celsius-water_temp)))

    cooking_time_mins = first_component*second_component / 60
    return cooking_time_mins

# Example usage

print(calculate_cooking_time(58, 4, 683))  # 5.130453449208272
print(calculate_cooking_time(34, 4, 683))  # 3.593544553884791

The embedded calculator below is a simplified version of the code. Simply input the weight of your egg, its initial temperature (usually room temperature), and your desired final temperature (63 degrees for a perfect runny yolk). The calculator will then provide the exact cooking time for your egg.

Default values have been set to most common egg size, average altitude of Canberra and average initial temperature of an egg straight out of the fridge. The calculations are based on placing the egg in boiling water.

You may be wondering, why 63 degrees? At this temperature, both the egg white and yolk achieve a custard-like consistency that’s absolutely heavenly. It strikes the perfect balance between runny and firm, making it the ideal accompaniment for a smashed avo toast.

The next time you’re craving a gourmet breakfast, don’t shy away from the 63 degree egg. With a touch of science, the right tools, and a little practice, you can achieve culinary perfection. Remember, practice makes perfect. So, if your initial attempts don’t yield the desired results, don’t be disheartened. Keep at it, and soon you’ll be whipping up 63 degree eggs like a seasoned chef.

P.S. With thanks to Charles D. H. Williams from University of Exeter for doing the hard work of deriving this eggcelent formula.