Chemistry meets Cuisine: Molten Chocolate Cake and Heat Transfer

This past week in Science and Cooking has been about studying heat transfer. Why is it so difficult to cook a steak to the correct temperature? Why do you preheat the oven to 180C when the centre of the roast is only supposed to get to 65C?

We visited (as I found out afterwards) Newton’s Law of Cooling and used the concept of the random walk learnt in the Diffusion topic to describe how heat energy moves through food.

But the best part is that the lab for this week was to make molten chocolate cake! Now, of course we were *supposed* to be scientific about it, taking temperature and ‘done ness’ measurements and so on. Except, it’s late and I feel like dessert and oh well, I guess I better get onto the lab! So, onto the process.

The recipe is as follows.


120g dark chocolate chips
~8 Tbsp oil or butter (107g) (NB – this is the US tbsp measurement, not the Aus one! Go by mass)
120g sugar
5 large eggs (275g)
60g flour
0.5g salt (pinch)

1 pot + metal bowl or 1 microwave safe bowl
1 medium bowl (wet ingredients)
1 small bowl (dry ingredients)
1 scale
1 fork or whisk

Method – Batter

Melt chocolate chips and oil/butter.
Microwave method: measure out chocolate chips and oil/butter into microwave safe bowl. Microwave on high 1min, mix the chocolate and oil until uniform, and then set aside to cool a bit.

20131126-215201.jpgStove method #1: place chocolate and oil/butter in a small pot and heat on low, while stirring, until it melts.
Stove method #2: fill another pot with some water and bring to a boil, then place chocolate and oil/butter in a metal bowl over the pot. Stir chocolate as it melts.
Mix sugar and eggs together well in medium bowl, then slowly add in chocolate mixture.

Weigh out flour and salt into small bowl, then mix it into the wet ingredients.


20131126-215845.jpgCooking the cakes

1 baking dish
6 mugs OR aluminum foil & bottle ~2” (5cm) across
1 cutting board
1 ruler
1 knife
1 oven mitt or tongs
1 thermometer

If using foil cups: Make 6 foil cups for cakes by taking 2 layers of aluminum foil and molding it around the bottom of a bottle with straight sides. Coat the cups or mugs with some oil to prevent sticking.
Preheat oven to 350F (177C).
Place 6 foil cups or mugs in a baking dish and pour batter about 1” high in each cup. If it’s hard to pour from the large bowl, pour into a thin-lipped cup (measuring cup, drinking cup, etc) first, then transfer to foil ones.
Prepare the water bath by pouring boiling water around the cups until about 1/2″ deep, being careful not to splash any into the cups.

20131126-220530.jpgCook for 18-21 mins (NB – as part of the lab, we were to take one out at particular time intervals and cut them open to check them and carry out measurements. This is the ideal timing for a nice molten centre)

Here was the first sample/puddle/delicious first try:

20131126-220716.jpgHere it is still in the ramekin:

20131126-220934.jpgAnd here’s the glorious final result. Yum!


One response to “Chemistry meets Cuisine: Molten Chocolate Cake and Heat Transfer

  1. Thanks for the recipe Chris! Looks deeeeeeeeeeeeee-lish!

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