Crème Brûlée

Introduction

There are two components to a crème brûlée. First, there is the custard that makes most of the dish. Second, is the dark caramel topping that we all are fascinated to see get made. The chemistry behind this delectable desert deals with the properties of the proteins in eggs and the caramelization of sugar.

Ingredients

  • 1 pint heavy cream
  • 1 vanilla bean
  • 1/2 cup sugar
  • 3 large egg yolks
  • 1 quart hot water

Directions

  1. Preheat oven to 325 degrees F
  2. Put cream, vanilla bean, and its pulp into a saucepan and bring to a boil
  3. Remove the mix from heat and allow to sit for 15 minutes
  4. Strain out vanilla bean
  5. Mix 1/2 cup of sugar and egg yolks until well blended
  6. Add cream in little bit at a time, while stirring continously
  7. Pour the liquid into ramekins
  8. Place the ramekins into a large cake pan
  9. Pour enough hot water to come half-way the sides of the ramekins
  10. Bake until creme brulee has set, which is when it just jiggles in the center (about 40-45 minutes)
  11. Remove and allow to cool
  12. Refrigerate for at least 2 hours and up to 3 days
  13. Remove from refridgerator and top evenly with sugar
  14. Use a torch to melt the sugar and make a crispy top

Eggs

Crème brûlée uses only the egg yolks. Egg whites are not used because they have a higher protein content. This higher content means that the proteins in egg whites will denature and reform stronger bonds (coagulate) more quickly and at a lower temperature than egg yolks. Egg yolks take longer to coagulate because their protein density is lowered by a higher fat concentration than egg whites. Egg whites are about 3% fat while egg yolks are 58% fat. The fat molecules act similarly to the interfering molecules in freezing point depression. They block the formation of new bonds between the denatured proteins, which slows down coagulation. By dragging out the process of coagulation and decreasing the amount of new bonds, we ensure that we get a creamy/silky custard, rather than a firm one like Jell-O.

The Importance of Cream

Egg whites begin to coagulate at 140 Fahrenheit, while egg yolks do so at 150 Fahrenheit. A mixed egg is in the middle at 145 Fahrenheit. Adding cream to our eggs raises the starting coagulation temperature to 170 Fahrenheit! This will further aid in slowing down the coagulation process, which will give a creamier custard. The cream is also important in tempering the eggs before they go into the oven. Tempering eggs is when you heat up the cream and then you add it very slowly into the egg mixture. This part is important because if you put a cold egg mixture into the oven there will be too much heat transfer at the beginning and it would heat up too rapidly, which would make the custard firm. By slowly adding in the cream, we get a warm egg mixture going into the oven. The warm mixture will not have as much of a heat shock and there will not be massive coagulation at the beginning.

Everybody Needs a Bath

Around 190-200 Fahrenheit, we start to get scrambled eggs. However, the recipe calls for the use of a 325 Fahrenheit oven. To make sure we get crème brûlée and not a mushy mess of scrambled eggs, we use a water bath. The water bath serves two purposes. Water cannot get hotter than 212 Fahrenheit in the oven, when it reaches that point it will use the extra heat energy to convert itself to steam. So the water helps bring down the temperature from 325 Fahrenheit to something closer to the coagulation temperature. And by doing so the water also helps the custard cook more evenly as well.

Caramel

The brûlée part in crème brûlée means to burn. This is where we use a torch to burn sugar. Caramelization is a non-enzymatic browning that occurs between carbohydrates. It is an oxidation reaction that occurs at about 320 Fahrenheit for sucrose (which is the sugar we use). The temperature of the butane torch flame is around 2,600 Fahrenheit, which is definitely high enough to make this reaction occur. This reaction creates hundreds of different products that that give the top caramel layer the buttery (diacetyl) and nutty (furans) flavor. A torch is used because we need a concentrated source of heat, if we were to crank up the heat in the oven to where caramelization occurs, the custard would cook into a rubbery blob. Also, torching caramelizes the sugar instantly, so you get a nice thin layer of caramel.

Sources:

  1. http://www.fatsecret.com/calories-nutrition/usda/egg-white%3Fportionid%3D29445%26portionam..%20
  2. http://healthyeating.sfgate.com/fatty-egg-yolk-4906.html
  3. http://thefinchandpea.com/2012/08/31/the-science-of-sexy-creme-brulee/
  4. http://www.foodnetwork.com/recipes/alton-brown/creme-brulee-recipe.html
  5. http://www.scienceofcooking.com/caramelization.htm
  6. http://en.wikipedia.org/wiki/Butane_torch

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