I Mustered Up a Custard

Custard  2/9/2014

My French Meringue cookies were delicious. The trouble with making meringue is that only egg whites are used. Since I’m currently a student on a budget, I do not want to let half of the cost of the eggs go to waste. There are ways to be frugal and flavorful, so in this blog I’ll show you how to make the most out of your ingredients.

What do you do with the leftover yolks from the meringue recipe?

You make custard.

A custard is a mixture of egg yolks with milk or cream. The custard ranges in consistency based on the amount of eggs used in the recipe. Custards can be eaten on their own or as a sauce. They are commonly included as fillings in pies, donuts, tarts, and éclairs. Custards were created in Europe during the Middle Ages, and were introduced to the Americas in the 1800s. You can thank the Europeans for America’s current versions of pudding, as custard-like recipes were incorporated into American desserts in the 1840s (1).

Remember protein denaturation that we discussed in The Meringue Breakdown? The same concept is applied to custard.

There’s one catch- Egg whites contain most of the protein in an egg. Egg yolks contain almost all of an egg’s fat.

The small amount of protein in egg yolks will unravel when heated, but it does so more slowly since the fat will restrict the final protein structure. Custards are formed using low heat, because high heat will denature proteins at a quicker rate. When the protein bonds reform in the presence of high heat, a scrambled egg consistency will occur. You will never form custard using high heat.

Milk is added to custards to make the coagulation process even more sluggish. Coagulation of egg proteins begins between 140°F and 150°F. Milk will raise this temperature by about 10 degrees because of the incorporation of extra fat (don’t even try to use skim milk). Using cream instead of milk will add more fat to the egg yolks, making an even richer custard (2).

Milk has a slightly higher boiling point than water because of the milk sugar, or lactose, present in its make-up. However, since milk is mostly made of water, the lactose will only raise the boiling point by a fraction of a degree. This is why sugar is usually added to custard recipes. Sugar adds sweetness to the custard, and raises the boiling point of the mixture (3). You’ll get a prolonged cooking process, which will make for an exceptionally smooth dessert.

Also, have you ever noticed that milk gets frothy at higher temperatures? Try making oatmeal with milk one time, and you’ll see what I mean. That’s because the main protein in milk, or casein, can withstand its structure under high temperatures. The addition of milk will help to stabilize the formation of the custard.

For the custard: 4 egg yolks, 1/2 cup granulated sugar, 1 tbsp all-purpose flour, 2 cups whole milk, 1 tsp vanilla extract, 1/4 grated lemon rind (optional), 1 cinnamon stick (or 1 tsp ground cinnamon)

For those of you who have just made meringue, use the four egg yolks that you have in the refrigerator from the meringue recipe. Otherwise, separate four egg yolks from four egg whites. Save the egg whites at your leisure.

Egg yolks and sugar.

Egg yolks, sugar, and flour.

Whisk the egg yolks and granulated sugar in a medium saucepan.This will help embed the granulated sugar into the egg yolks. Use a wooden spoon to mix the flour into the egg yolk and sugar mixture. Set this saucepan aside for now.


Milk, vanilla extract, grated lemon, cinnamon stick.

In another sauce pan, add the whole milk, vanilla extract, grated lemon rind (optional), and cinnamon stick (or ground cinnamon). Bring the contents of the pan to a boil and immediately remove it from the heat.

You will need a strainer and patience for this next step. GRADUALLY pour the hot milk mixture through a strainer into the saucepan with the egg yolks, sugar, and flour. Do this slowly because adding a lot of heat to the egg yolk mixture at one time will cause the egg yolks to cook, instead of simply raising their temperature. Gently warming the eggs will prevent the yolks from clumping.

We are tempering our egg yolk mixture by using the hot components of the pan with the milk.

The strained mixture. No clumps to be found!

The strained mixture. No clumps to be found!

Stir the egg yolk saucepan and its contents with a wooden spoon as you pour in the hot mixture to distribute the heat evenly.

The milk is frothy from simmering the mixture at low heat.

The milk is frothy from simmering.

Simmer the final mixture on the stove top at very low heat.  DO NOT let the contents boil. This will prevent the egg yolk structure from solidifying properly.

While the contents are simmering, stir it constantly for about 5 minutes. In this five minute range, you will see your custard becoming thicker and smoother.

If you start to see a grainy texture, then you have overheated your custard. I left my custard on the heat for slightly too long, but this works out in your favor so you will get to see the differences!

Don’t worry, the flavor of the custard will still be awesome, but you won’t have a hefty, pudding-like dessert.

Immediately remove the pan from the stove once the custard texture is obtained, and allow it to cool for a few minutes. You can also stick the saucepan into an ice bath if you feel inclined. Stir it occasionally as it cools to prevent a skin from forming on the top. Once the custard is cool, chill it in the refrigerator until you are ready to eat it!



You’ve probably noticed that I didn’t bake anything during this blog post. I not only wanted to show you how to use your leftovers wisely, but I also wanted to demonstrate how to create a proper custard. Now we can explore the baking world of pies, tarts, and quiches!

Rough estimate of the custard's nutrition facts, using the USDA nutrient database.

Rough estimate of the custard’s nutrition facts, using the USDA nutrient database.


1. “History Notes–puddings.” The Food Timeline. Accessed 09 Feb. 2014. <http://www.foodtimeline.org/foodpuddings.html#custard&gt;.

2. “Creme Brulee: The Science Of Sexy.” The Finch and Pea. Accessed 09 Feb. 2014. <http://thefinchandpea.com/2012/08/31/the-science-of-sexy-creme-brulee/&gt;.

3. “Q & A: Boiling Point of Milk.” Physics Van. Accessed 09 Feb. 2014. <http://van.physics.illinois.edu/qa/listing.php?id=1451&gt;.

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