EGGS-CAPTIONAL: the scientific formula where M stands for mass, T for temperature
and t for cooking time.

A British Scientist says he has cracked the mystery that has stumped us all - the recipe for the perfect soft-boiled egg.

But the formula above is not exactly what you would expect to find in a cookbook, and by the time you work it out your egg will be well and truly boiled hard.

New Scientist magazine invited Dr Charles Williams, of Exeter University, to "eggs-trapalate".

The physicist based his calculations on the "heat-diffusion equation for spherical objects".

'M' stands for mass, 'T' for temperature and 't' for cooking time, and the constant for proportionality depends on the specific heat capacity and thermal conductivity of the egg. Get it!

If the egg is placed straight into a pan of boiling water it will be ready when the temperature of the yolk has risen to 'T-yolk' or about 45 degreesa.

According to Dr Williams' formula, a medium egg (50g) taken straight from a 4 degree refrigerator needs 4 mins 30 seconds in boiling water to give it a perfect centre.

A smaller egg of 47g from the fridge takes 4 mins 15 seconds to cook and a larger 67g takes 5 min 30 seconds while a medium egg stored at room temperature of 21 degrees takes a few seconds under 4 minutes.

But Melbourne restauranteur Andrew Blake says you don't have to be a rocket scientist to boil the perfect egg.

"The way we were taught at school has had hundreds of years of practice supporting it," he said.

Simply, he said, room temperature eggs should be put into simmering water - little bubbles as opposed to big ones when the water is boiling.

A soft white and yolk will take 3 mins a set white and partially set yolk takes 5 mins, and for a hard white and yolk set the timer to 8min, he said.

Food writer Beverley Sutherland-Smith has her own special method. She believes an egg has to be started in cold water that is brought to the boil. Then you count to 10, take the water off the heat and wait for a minute.

"You can only be scientific if everybody cooks their egg using the same variables," she said.

The Hilton Hotel in Melbourne serves more than 80 soft-boiled eggs daily but chef Stefano Verrillo said he thought the whole thing was a scientific beat-up.