Allegedly a glass of hot water will freeze faster than a glass of cold water. I say allegedly because it’s something that is often claimed but quite hard to prove or disprove. Anecdotal evidence suggests it is so, but as we all know, that ain’t proof.
Having said that, some years ago New Scientist sparked off many investigations into this phenomenon and it really does seem to be the case. The general consensus is that the cold water freezes from the outside fairly promptly but the water held within cannot lose heat very rapidly, insulated as it now is in an ice shell. Hot water, on the other hand loses heat uniformly throughout its volume as the internal currents that exist as a result molecules with lots of energy jiggling about cause the water to continually mix. This continual mixing allows more heat to be lost from more of the water. These convection currents can be seen if you put a drop of food colouring into each of a glass of cold and hot water. The hot water will become more uniformly coloured quicker than the cold.
Convection happens within all fluids at all temperatures above absolute zero but the speed increases with temperature – more energy means faster jiggling molecules. Solid materials do not experience convection currents as there’s nowhere for the molecules to jiggle to.
This then brings us to the legendary chocolate fondant, that unctuous, delightful, chocolatey bit of heaven that is cakey on the outside and all gooey and rich in the centre.
The secret is to cook them just enough that they remain uncooked in the centre. Simple as that. Overcook them and they turn into a fairly uninspiring cake.
Well, that’s the theory at least. The problem that I have found in cooking fondants is that you’ve got to really know your oven to get them spot on. Is it ten minutes at 200 or twelve at 190? It’s one of those things that one has to practice to be sure. Two minutes either way can make the difference between too much raw cake mix and a chocolate scone.
I always get a “fingers-crossed” moment when a contestant attempts a chocolate fondant on Masterchef because having mastered them in my own kitchen I can only imagine the trickiness of cooking them in a completely unfamiliar environment, under intense scrutiny. But it isn’t just the oven, oh no.
I have no empirical proof that this is the case but my supposition is that the internal temperature of fondant mixes as they hit the ovens in the Masterchef studio is higher than in the contestants’ homes. A fondant is usually a mix of butter, chocolate, sugar, flour and eggs which are variously melted and folded together. As the mixture is distributed to ramekins it begins to cool and if allowed to cool sufficiently the fat will begin to thicken and eventually solidify.
What this means is that a fondant that is left standing for even just half an hour will be thicker and have slower moving internal convection. But if one has limited time and is in a rush it is a good bet that the mixture will go in the oven warmer and runnier than if one has more time.
My experiments suggest that not only does a warmer fondant cook in a shorter time, but critically the window within which one has to work is much, much smaller.
That is not to say that one cannot make chocolate fondants quickly, knock up the batter and straight into the oven, but that is where knowing your oven and being well practiced is vital. By starting from a cooler mixture you can reduce the internal heat-driven mixing, or convection currents, which would otherwise result in the cake cooking through more evenly.
Specifically, the outside of the fondant will go through a melting, runny phase and then cook as the starch in the flour absorbs water and the wheat and egg proteins cross-link to form a resistant matrix. If the mix is cool then all this will happen before the core has begun to melt, if the mix is too warm the runny warm outside will flow into a mix with the slightly cooler but still running centre and we have same situation as with the hot and cold water (only with the thermodynamics working in the other direction!)
So there it is. My suggestion is that the reason most chocolate fondants on Masterchef don’t go well is because the convection currents in the mixture are more rapid – and this is because time pressure does not permit a cooling of the mixture that might otherwise happen at home. The latitude one has to get a fondant right is massively reduced at higher internal temperatures.
I make this supposition because clearly everyone who has attempted a fondant on the TV has practiced and practiced at home but the failure frequency is too high to be mere chance. There must be another contributing factor. Unfamiliar ovens are one thing but ultimately it’s the time pressure that leads to a too warm mixture that results in such a tiny window between under and overcooked that is to blame.
If you want to get a chocolate fondant right, and have never tried one before, you will hugely maximise your chances of success by cooling them first. It is relatively straightforward and the physics of fluids allows us to see why. An expert who knows their oven and knows their mix well can get them spot-on without breaking sweat. But I think it’s a good idea to start by giving yourself the best chance of success. But then I would say that because my business is teaching people how to cook!
