This delicious Spanish dessert exemplifies the last 2 posts: the liquid to gel transition and the Bain Marie. The quantities here are for about 6 people.

Ingredients

6 eggs
1/2 litre of milk
sugar

Very hot sugar can crack a ceramic pot.

Very hot sugar can crack a ceramic pot.

Cover generously the bottom of a metallic oven mold with sugar and then caramelize it directly on the gas fire. If you don’t have gas, you can also melt the sugar in the microwave (do not use a metallic recipient in that case!). Be careful because sugar gets very hot (needs to reach at least 160ºC/320F to be caramelized) and also it burns fast giving a bitter taste (just a bit over caramelizing temperature: 177ºC/350F) so, especially if you do it in the microwave, be sure to open and stir every 10-15 seconds. As  you can see in the picture, the high temperature of the sugar in the microwave even managed to crack my ceramic pot. Once the sugar has a light brown colour, turn the fire off and let it rest for a moment.

Meanwhile, mix the milk, eggs and 6 table spoons of sugar in a jar. Then just pour the mix onto the oven tray with the caramelized sugar and put it in the oven in a water bath. Let it bake for about 30-40 minutes at 180ºC (356F). To check that it is properly cooked inside, insert a needle in the flan. If it s done, it will come out clean. Let it cool down and then put it in the fridge to cool even further. After a couple of hours it will be ready to eat. Use a knife to separate the flan from the mold, flip it upside down onto a plate and enjoy!

As you can see the flan has now a gel consistency; the egg proteins have denaturalized and formed a permanent network trapping the milk with sugar inside it: the mix has undergone a liquid to gel phase transition. I did an individual portion this time:

Cooking Flan is a liquid to gel phase transition.

Cooking Flan is a liquid to gel phase transition.

Why do we need the Bain Marie? For two reasons. The first is that, if we are not careful, the sugar in the bottom will reach 177ºC(350F )and burn. The second is that the liquid mixture will start to boil when heated above water’s boiling point creating bubbles that will get trapped into our gel and ruin the pudding texture.

To see this, I cooked two individual flans: one in a water bath and the other just directly in the oven. After a few minutes, I could see how the volume of the latter was augmenting due to the bubbles under the surface. Compare the flan that was cooked in a water bath (left) with the other one (right):

Flan cooked in a water bath (left) and without it (right).

Flan cooked in a water bath (left) and without it (right).

These bubles resulted in the gel structure being ruined inside and the caramelized sugar being burnt:

Flan cooked directly in the oven (left) and in a water bath (right).

Flan cooked directly in the oven (left) and in a water bath (right).

As you can see, the one cooked in the water bath looks much tastier (and indeed it was :)!).

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