Eggnog science – On steeping spices and whipping egg whites

There are plenty foods you will only come across in a certain time of year and eggnog is definitely one of those. If you’ve never heard of eggnog you’re probably not the only one. Eggnog is a typical Christmas drink, made with whipped eggs and lots of spices. It’s rich and warm and smells great, so you’ll cuddle up inside and how the warm mug in your hands while smelling it.

The spices have literally seeped into the drink and thanks to the egg proteins it’s soft and fluffy. The molecules have arranged themselves in such a way that it’s become soft and flavorful, a great warm snack. So together with that warmth and great smell sits some science that we’ll be exploring here.

Making eggnog

There are a lot of different ways to make eggnog. The most basic recipe consists of mixing sugar & milk with egg yolks and then adding some whipped egg whites. The version at the bottom of this recipe is a little more complex though, to add some extra flavour and spiciness to make it even more seasonal. This rich flavourful version is a three step basic process. At the end of this post you can find a complete recipe, but let’s look at those three steps first:

  1. Steep your lovely smelling spices in a liquid, cream and milk for instance.
  2. Thicken up your spicy smelling liquid using egg yolks
  3. Make it just a bit more fancy by adding in some whipped egg whites

Steeping spices vs. an extract

In other posts you can read about the extraction of vanilla and cinnamon. These whole spices contain a lot of flavour and aromas, but they have to be extracted from the spice themselves. Most of these flavour components don’t dissolve well in pure water though. Instead, they are fat soluble. A way to overcome this is to use alcohol to extract the flavour. This does take some time though. Another method is to steep them in warm liquid for some time, preferably one with some fat in it. This is similar to what you would do with a bay leaf when making soup for instance.

The high temperature of a liquid will increase the movement of the flavour molecules in your cinnamon stick or vanilla bean. As a result, these molecules leave the spice more quickly and easily. Since most of the molecules dissolve best in a fat or oil, you will often see cream or whole milk being used. The fat molecules in these two liquids will help extract and hold on to the flavour from your spices.

When making eggnog you’d want to use either of the two methods: make an extract in advance, and use the extract to add flavour, or seep the spices in a warm liquid to take out the flavour on the spot. In the recipe below we’ve seeped the spices. If you do so, keep in mind that this takes some time. It’s good to heat up the mixture and leave it to sit for a while. However, when you’re using the extracts, no need to heat up the liquid to seep them. Instead, since all the flavour has already been extracted before, you actually want to keep it somewhat cooler since the heat might actually cause a loss of flavour. When using the extracts, best to add them at the end, after adding the egg yolks.

The role of the egg yolk

In eggnog a raw egg yolk can be added. However, not everyone likes to eat raw eggs or feels safe eating raw eggs. This recipe therefore contains a slight cooking step of the egg yolks which has another advantage: it thickens the eggnog.

There are quite a lot of examples of foods where egg yolks are used for thickening. A Hollandaise sauce or a custard for an ice cream both require egg yolks to thicken the mixture. Egg yolks can thicken a sauce when they’re heated. The heat will cause the proteins in the eggs to unfold, coagulate and form a protein network. An egg yolk thickened sauce is generally smoother and more flavourful than a flour thickened sauce (the flour leads to a slight loss in flavour).

In this eggnog the egg yolk has exactly that function. By heating the egg yolk gently (you don’t want to heat egg yolks too vigorously or the proteins will curdle instead of set gently!), they will thicken the eggnog just slightly, making it a bit more creamy. Also, the gentle, but prolonged heat can kill off micro organisms. However, if you use it for that purpose, you might want to check the temperature a bit more closely, whereas if you’re only thickening the mixture you can use visual clues to see whether it’s done.

The role of alcohol

Eggnog often contains a decent amount of alcohol, which is added at about this point in the recipe. Partly this is added for taste of course, but it can also serve well to preserve the eggnog. If enough alcohol is added it will prevent further growth of micro organisms. If you’re using raw eggs in your eggnog you wouldn’t be able to keep it for too long (max. 1 day) without any alcohol. However, by adding enough alcohol it can be kept for days or even weeks.

Topping it off, with some foam

Last but not least, eggnog is topped of with some foam. Just before you decide to drink this eggnog, re-heat it slightly (don’t forget about the curdling of the egg yolks!), whip up some egg whites and mix those through.

Those egg whites are raw, so if you’re not comfortable using raw eggs or if you’re at risk for becoming sick, use pasteurized ones, or leave it out (although that would make the drink pretty dense to drink). No need to dive into the science of egg white foams here since you can find plenty of information on foams in other articles on this website: chocolate mousseItalian meringue and meringues (Dutch schuimpjes).

 

Eggnog recipe

With that new knowledge in mind, it’s time to make the eggnog, smell the spices, experience the thickening and enjoying the foam. The recipe below is a combination from those of Jamie Oliver and the method used by Macheesmo. Enjoy and please feel free to adjust to your preferred tastes.

Eggnog
 
Prep time
Cook time
Total time
 
Author:
Recipe type: Drinks
Serves: 8 large mugs
Ingredients
  • 700ml milk (I used full fat, but since it's pretty heavy by itself, I might use skimmed next time to make it a little less filling)
  • 250ml cream
  • 3 cinnamon sticks
  • 1 vanilla bean pod (or 2 tbsp of homemade vanilla extract! which is what I did)
  • 1tsp nutmeg
  • 5 eggs
  • 130g sugar
  • 150ml bourbon
Instructions
  1. Add the milk, cream, cinnamon, vanilla and nutmeg to a pot and bring to the boil. I left it simmering on a low heat for another 10 minutes before taking it from the fire. It's best to leave it for at least another 30 minutes for all the flavours and aromas to leave the spices and sit in the milk/cream, but if you don't have the time, you can go ahead immediately.
  2. Split the eggs into yolks and eggwhites.
  3. Whisk the sugar and egg yolks together.
  4. Remove the sticks and pod from the milk/cream mixture and bring the milk/cream back to the boil and slowly pour about half the mixture with the yolks and sugar while continuously whisking.
  5. Pour everything back in the pot and heat slowly while continuously whisking. I don't like the idea of using raw egg yolks so bring it back to approximately 60-65C. This not only pasteurizes the egg yolks, it will also thicken up the mix slightly. Do not heat too fast or without stirring, the yolks can start to curdle up.
  6. Take from the heat and add the bourbon (optional). In our case we split the mixture in half at this point, adding half the bourbon to the one half and keeping the other alcohol-free. Leaving out the alcohol will make a very sweet, but flavourful mix whereas the alcoholic version tastes noticeably different and allows less to taste the individual spices.
  7. You can now store the mix in the fridge for 1-2 days.
  8. Shortly before serving, take the egg whites (store those in the fridge as well) and whisk them up to stiff peaks. Fold them through the milk/cream mixture and serve immediately. If you want, you can decorate with some cinnamon or cocoa powder on top!
  9. Enjoy!

 

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