Engineers understand how to cook!
Today is Presidents’ Day. In our house that means that all students (our kids) and teachers (my husband) are sleeping in and I have to go to work. My family’s business votes on 10 holidays to observe each year and the consensus is always for the summer holidays and very long weekends. I don’t mind getting up when everyone is sleeping because these days mean that I have the house to myself as my loved ones blissfully slumber the morning away. To take advantage of this morning I tried to make soft-boiled eggs. I’m 45 years old and I don’t know how to soft boil an egg. Sure, I probably had a cookbook somewhere telling me how to properly soft-boil eggs, but I wouldn’t admit such defeat (there’s a life theme in this sentence). Besides, how hard could it be?
After three tries and four eggs, I ended up with one egg that was pretty close and one perfectly soft-boiled egg. After enjoying the eggs, I decided to check out my favorite cooking site, Cooking for Engineers. I couldn’t find a recipe for soft-boiled eggs - I’m looking for some kind of chart with times and yolk consistencies - but I found a delicious looking recipe for Orzo Risotto with Buttery Shrimp.
A further search for a chart led me to the University of Exeter School of Physics and The Science of Boiling an Egg by Charles D.H. Williams:
A Formula for Soft-Boiling Eggs
The Derivation
To obtain a simple formula the problem must be idealised somewhat, so the egg will be treated as a spherical homogeneous object of mass M and initial temperature Tegg. If the egg is placed straight into a pan of boiling water at Twater, it will be ready when the temperature at the boundary of the yolk has risen to Tyolk~63°C. With these assumptions, the cooking time t can be deduced by solving a heat diffusion equation.
The Result
The full derivation (PDF, 19kB), which can be viewed with the free Adobe Acrobat Reader, is quite complicated but the final result is relatively simple:
resource.
where ρ is density, c the specific heat capacity, and K thermal conductivity of ‘egg’. According to this formula, a medium egg (M~57 g) straight from the fridge (Tegg=4°C) takes four and a half minutes to cook, but the same egg would take three and a half minutes if it had been stored at room temperature (Tegg=21°C). If all the eggs are stored in the fridge, then a small (size 6, 47 g) egg will require four minutes to cook, and a large egg (size 2, 67 g) will take five minutes.
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