coffee creme brulee

Science of creme brulee

Creme brulee is definitely one of the more decadent, luxurious desserts out there, while still being widely available. It’s a soft and silky creme on the inside covered with a crispy brown sugar top. Creme brulee can be finicky to make, but, as long as you understand the science of your egg yolks & sugar well, it becomes a lot easier to make.

Three ingredients in creme brulee

The tricky aspect of making a creme brulee sits in the process itself, not the ingredients, since you need only three: cream, egg yolks & sugar. You need more if you want to add some additional flavour (more on that later). Each ingredient plays a crucial role:

  • Cream: provides richness & creaminess
  • Egg yolks: firm up the creme brulee, without them, your mixture will remain liquid
  • Sugar: sweetens the dish and makes that crunchy brown layer on top

Making creme brulee – controlling time & temperature

When you make creme brulee you really try to achieve three things:

  1. Dissolve the sugar in the cream – to make it smooth and without any grittiness
  2. Cook the egg yolks – to firm up the creme brulee
  3. Caramelize the sugar – to make a crispy layer

For all of these steps the main thing you have to pay attention to is how you control your time & temperature. You don’t want to scramble your eggs, nor burn the sugar. Controlling these well is the crux to a good creme.

1. Dissolving sugar

A final creme brulee should be super soft and smooth. You don’t want any clumps or bits in the creme brulee. In order to do so it is important that the sugar fully dissolves in the cream. If it doesn’t dissolve well, it might give you some inconsistency in the texture and some crunchy bits and pieces.

This is why most creme brulee recipes start by slightly heating your cream to dissolve that sugar. You could also use icing sugar here, that dissolves even more easily, thanks to the smaller particle size and larger surface area.

2. Cook the yolks

In order to transform that liquid cool creme brulee mixture into a wobbly slightly firm creme brulee, you need the power of egg yolks. The egg yolks are what make or break your creme brulee: undercook them and the creme brulee will still be liquid, over cook them and they might curdle and split.

The molecules in the egg yolk that are the cause behind all of this are the proteins. Egg yolk is made up of mostly moisture, fat and egg yolk proteins. By heating the proteins in the egg yolk they will unfold themselves slightly. This way they are able to bind water and thicken the creme brulee mixture.

Heat the proteins too much though and they will unfold even further and loose their structure, causing them to push out water of their texture instead of binding it.

lemon custard pies
These lemon custard tarts also use egg yolks to firm up.

Cooling down & heating up

Therefore, never add your egg yolks to the hot mixture of cream and sugar. The high temperatures will cook the yolks before they even have a chance to adjust. Always cool the cream mixture down slightly, or pour it into your egg yolks slowly (while whisking) to even out the temperature. After you’ve mixed them together, they’re good to go into the oven to get those egg yolks setting.

When you bake creme brulee in the oven, you have to consider heat transfer phenomena. The outside of the creme brulee will heat up more quickly than the inside. If the temperature difference is too large, the outside might over cook before the inside has time to cook. To prevent this, you will often see that recipes call for baking the creme brulee in a tray of hot water. This way, the outside of the trays cannot become warmer than 100C, the temperature of boiling water, limiting the temperature differences and giving a more even cook.

Instead of placing the trays in hot water in the oven, you could also use a pressure cooker for similar results, just as you would for a cheesecake.

3. Caramelizing sugar

Once your creme brulee comes out of the oven, set, but not dry, there is one step left to do: caramelize that sugar on top. You do this by sprinkling some additional sugar on top of the creme brulee and using a blow torch or grill in the oven to heat the sugar. The very high temperature (and the fact that the sugar is dry) will cause the sugar to caramelize. This is a complex series of chemical reactions during which the sugar transforms into a brown crispy layer with a more complex, less sweet flavour to it.

Since you’re adding a lot of additional heat, it is important that you don’t overcook the pudding on the bottom. You don’t want to scramble your eggs at this point! This is why it’s best to cool down the creme brulee before trying to caramelize it, it will take longer for the center to get hot becuase of the additional heat.

making eggnog adding the spices
Infusing flavour into liquids is also something you do when making eggnog!

Adding flavour

When it comes to adding flavour to a creme brulee you want to infuse the flavour as opposed to necessarily adding ingredients with the flavour (e.g. pieces of apple). Since the structure of a creme brulee is quite delicate it can’t handle a lot of additional ingredients.

The simplest way to do this is to let the flavour seep into the cream + sugar mixture for a while. You can add the flavour ingredient (e.g. coffee beans) into the cream at the start. That way, you heat it up with the cream + sugar and it has time to release its flavour while it’s cooling down. This works very well for spices, teas, etc. The reason the flavour seeps out well is that the cream contains both fat & moisture, providing a nice environment for flavour molecules that prefer to sit in either of the two. (It’s a pretty similar process as extraction.)

cofee soaking in creme brulee cream sugar mixture
Coffee seeping into the cream + sugar mixture for the creme brulee. You can do this for pretty much any flavour at this point, vanilla works well, as do spices (e.g. cinnamon sticks).
Yield: 4 portions

Coffee creme brulee

Coffee creme brulee

This creme brulee is enriched with some coffee flavour, without being too overpowering. The recipe is based on one from America's Test Kitchen (The complete America's test kitchen cookbook 2001-2016), with a few tweaks.

Makes 4 regular sized portions. You will need ramekins or leak-proof small oven dishes with low sides as well as a large heat proof tray that will fit all four comfortably.

Prep Time: 1 hour
Cook Time: 30 minutes
Total Time: 1 hour 30 minutes

Ingredients

  • 25g whole, roasted coffee beans (or 1 tbsp ground coffee)*
  • 290g whipping cream (high fat content)
  • 30g sugar
  • 4 egg yolks**
  • 4 tsp of granulated sugar (or a sugar with a rough/large particle size)

Instructions

  1. Using a rolling pin or meat hammer, crush the coffee beans into smaller pieces. You could do this inside of a sturdy plastic bag.
  2. Add the beans, cream and 30g of sugar in a pot. Bring the cream to the boil and stir to ensure the sugar is fully dissolved.
  3. Turn off the heat as soon as the cream is boiling and cover with a lid. Leave to sit for at least 30 minutes, preferably 2 hours to ensure as much flavour as possible seeps out of the beans.
  4. When the cream has cooled down (to room temperature, or a few degrees higher, cool enough to touch), whisk in the egg yolks. Ensure they are mixed in well.
  5. Pre-heat the oven at 160C (325F) and boil enough water to fill the large tray in which you'll be putting the ramekins half way.
  6. Take a heat proof tray large enough to fit your ramekins and able to handle large temperature fluctuations (you'll be pouring in boiling water).
  7. Pouring through a sieve to get rid of the coffee pieces, fill your ramekins or oven dishes with equal amounts of creme brulee mixture.
  8. Place the ramekins into the large tray and place into the pre-heated oven. Pour the boiling water into the large tray, take care not to add water to the creme brulee mixture or it will become too diluted.
  9. Bake in the oven for approx. 25 minutes (the thicker your layer, the longer they will take). The creme should be slightly firm to the touch and wobbly, it shouldn't be liquid anymore (you can use a thermometer as well, they should be about 75C/170F).
  10. Take the ramekins out of the oven and leave to cool down, preferably to fridge temperature, but at least down to room temperature. If it is too warm when going into the next step the center may overcook and become too liquid/soft again.
  11. Sprinkle the 4 tsp of sugar over the ramekins. It should cover the surface, without being a thick layer. Adjust the amount when necessary (it depends on the size of your ramekins).
  12. Turn on the grill of your oven or use a blowtorch to caramelize the sugar on top.
  13. Serve and enjoy!

Notes

* Ground coffee has a larger surface area per gram than whole coffee beans, even if they are broken down. Therefore, a lot more flavour will seep out so you should use less of it. If you use ground coffee, be sure to use a strainer with a fine enough mesh to remove the powder again.

** Use the whites for a Swiss or Italian meringue!

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