I have a master's degree in food engineering. Professionally, I've worked in the cheese, wine, and coffee industries.
Chemistry of Pudding
The science of pudding may never have crossed your mind. But contained within a simple pudding recipe lies several interesting and complex chemical reactions, balanced and honed through centuries of trial and error.
Only in the last two centuries did science evolve to allow us to understand why these complex foods react the way that they do. The following article will take a look at each ingredient as well as each processing step. By understanding the underlying science we can confidently change recipes that use these ingredients and troubleshoot any problems that arise. Gone are the days of fearful cooking!
In This Article
- Basic recipe: chocolate and vanilla pudding
- Science behind each ingredient: milk, sugar, egg yolks, corn starch, salt, butter/cream, vanilla, chocolate
- Science behind each culinary technique: mixing dry ingredients separately, adding milk slowly, premixing egg yolks, cooking, adding the butter/chocolate/vanilla last, straining, refrigerating
Basic Vanilla and Chocolate Pudding Recipe
This pudding recipe is a simple, no-frills recipe that I like to use to make a mix of chocolate and vanilla pudding. I usually make the vanilla pudding first, then use half of it as the basis for my chocolate pudding. It is interesting to watch the integration of the chocolate into the pudding mixture and see what it does to the texture.
I notice that my chocolate pudding is typically smoother, richer, and more consistent. I attribute this to two characteristics of the chocolate: one is the added fat, which is admittedly rather low in the vanilla recipe. The second is that the chocolate itself also contains a good amount of lecithin, which helps to bind all of our other ingredients together.
- 2/3 cup table sugar
- 1/4 cup corn starch
- 1/2 teaspoon salt
- 4 1/2 cups milk
- 6 large egg yolks
- 6 tablespoons unsalted butter (see note below for a no-butter option)
- 2 teaspoons ground vanilla bean
- 3 ounces dark chocolate
If you'd prefer not to use butter, or if you've run out, you can substitute 1 1/2 cups heavy whipping cream. In this case, the recipe will require slightly less milk—use 3 3/4 cups (instead of 4 1/2 cups). If using this substitution, add the cream with the eggs before cooking.
- In a bowl, combine the sugar, corn starch, and salt. Mix thoroughly and mash out any lumps.
- Pour the dry ingredients into a large saucepan.
- Slowly whisk the milk into the saucepan, adding progressively more milk only once you are sure that the dry ingredients have been well incorporated.
- In a separate bowl, whisk the egg yolks until slightly frothy; then whisk into the pudding base.
- Continue whisking the pudding over medium heat. Once a simmer is reached, reduce heat to just high enough to maintain heat, and stir pudding with a spatula, scraping sides.
- Continue cooking at a simmer (not a boil) until it is sufficiently thickened, and pudding drizzled on the top of the cooking mixture retains a distinct memory.
- Remove from heat. Stir in butter and ground vanilla bean until a consistent mixture is achieved.
- Strain half of the mixture through a mesh sieve into the serving containers you will be using. This is your vanilla pudding.
- To the remaining half of the mixture, stir in the chocolate, stirring every 30 seconds until completely incorporated.
- Strain the chocolate pudding through the mesh strainer into serving containers on top of the vanilla pudding.
- Refrigerate until set.
- Serve and enjoy!
Milk is an essential ingredient of every pudding, and it supplies several important characteristics to the finished product.
- It provides five important components: water, sugar (lactose), fat, protein, and minerals. It is packed full of the macronutrients that we need to survive.
- Good milk should be almost flavorless.
- Heating milk generates flavor molecules called lactones. When separated, lactones have aromatic hints of peach, coconut, and other fantastic flavors, but together they give us a nice creamy pleasant cooked milk aroma.
- Depending on the type of pudding you are making, extensive heating of milk can also caramelize the sugars and proteins in a Mailard browning reaction. We know this product as dulce de leche.
- When making pudding, it doesn't make a big difference whether you use whole milk or skim milk, as long as you are adding enough cream, butter, or cocoa fats back into the pudding. Pudding without enough fat will seem flat and boring rather than decadent and indulgent.
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The 6 to 7% lactose present in milk does not provide enough sweetness for the pudding, so we need to add more.
- Typically the sugar used in pudding is simple table sugar comprised of crystalline sucrose.
- Most home pudding makers only need to worry about the total sweetness of their pudding when adding a sweetener to pudding. However, in other applications that could see the migration of moisture (layered pudding with cake for example), the type of sugar used in pudding can act to change both the freezing point, boiling point, and the water activity (affinity for water) of the finished product.
- Different sugars have different levels of sweetness; however, each sugar has approximately the same effect per ounce on the water activity, boiling point, and freezing point. This means that the use of a different sugar will allow the addition of more or less total sugar, giving the pudding maker the ability to change the characteristics of their pudding without impacting the sweetness of the product.
Ingredient: Egg Yolks
The egg yolk plays several very important functional roles in the pudding-making process.
- Egg yolks are rich in fats, proteins and phospholipids.
- They help act as a thickener (though we'll need additional thickening help from corn starch).
- They yield a very tender creamy custard, but without additional thickeners (such as the commonly used corn starch, which also appears in our pudding recipe), these same custards are easily overcooked into a lumpy mess.
- Harold McGee, in the seminal food science work On Food and Cooking, defines the minimum number of yolks for a properly thickened custard without additional thickeners as three yolks per cup. This quantity of egg contributes a strong egg flavor, which is not always desirable in puddings.
- The same characteristic of egg yolk that makes it a weak thickener actually makes it an emulsifier, as well.
- It is the presence of lipid-bound proteins and phospholipids such as lecithin that allow butter, cream, and other fats to be effectively mixed into the pudding without separation, much in the same way that egg yolk is essential for emulsifying oil to make mayonnaise.
- From a flavor standpoint, choose eggs that are as fresh as possible. Off flavors increase from the moment an egg is laid.
Ingredient: Corn Starch
Corn starch is an extremely common thickener used in everything from pudding to delicious Thanksgiving gravy.
- Corn starch is a type of thickener called a hydrocolloid thickener.
- The basic molecular building block of corn starch is a sugar called glucose. The glucose molecules are linked together in two forms; amylose and amylopectin. Amylose is a straight chain sugar polymer which does not branch. Amylopectin is a branched-chain sugar polymer. You can think of amylose as a roll of twine, and amylopectin as a spider web.
- Corn starch contains about 20% amylose and 80% amylopectin. Because of the long straight character of amylose, it is a much better thickener, and when using corn starch as a thickener, it is actually this 20% that we are after.
- Table salt, or sodium chloride, is a simple ionic mixture of two elements: sodium, which goes by the abbreviation Na, and chlorine, which goes by Cl.
- When dissolved in water, salt forms the anion chloride (Cl-) and the cation sodium (Na+). These ions play an important role insofar as they interfere with the egg proteins by competing to bind to the active sites. This competition of ions increases the temperature needed to set the egg, which helps to ensure that it stays delicate.
- Salt also functions to enhance flavor.
Ingredient: Butter or Cream
Both butter and cream function very similarly in pudding.
- They are both added for their fat.
- Unsalted butter may also have some additional flavor properties, such as the presence of diacetyl, either from addition during butter manufacturing or fermentation. Diacetyl is the quintessential "butter" flavor that can be found in movie theater popcorn.
- The function of both our egg and corn starch (hydrocolide thickener) acts to emulsify this fat into the body of the pudding. Milk fat naturally occurs in fat globules, coated in a protein-lipid membrane, which allows dairy fats to be easily emulsified into the pudding.
- Vanilla is added strictly for the flavor that it contributes to this dish.
- Using real vanilla bean adds a nice flecked appearance to the finished pudding, as well.
- Vanilla is actually a cured seed pod from an orchid. The growth, harvest, curing, and export of vanilla is a thing of incredible complexity.
- The flavor characteristics of vanilla stem from a combination of the raw seed pod and the treatment and curing process which it undergoes.
- Depending on where the vanilla pods are harvested and how they are processed, very different flavor profiles can emerge.
Chocolate is really an optional ingredient in this pudding recipe, but if you do choose to add it, it will act to change the texture and flavor of the finished pudding. This is because of two different characteristics of chocolate:
- Chocolate contains a very high amount of cocoa fat, labeled as cocoa butter on its ingredient list.
- Chocolate also contains lecithin (a general term for phospholipids), which is a great emulsifier. The additional lecithin in the chocolate, much like the lecithin in the egg yolk, helps to pull together the different proteins, water, and fats in our pudding. Note: Not all chocolate contains lecithin, so be sure to check the ingredient list of the chocolate you use.)
Process: Mix the Dry Ingredients Separately
Mixing the dry ingredients separately is a good way to break up the sometimes clumpy corn starch. A smooth mixture of dry ingredients helps ensure even incorporation with the milk.
Process: Slowly Mix in the Milk
By mixing the milk into the dry ingredients slowly, the initial viscosity of the solution is very high. This highly viscous mixture allows us to generate a force known as sheer, which helps to break up any small pieces of corn starch that may not otherwise dissolve in the solution.
Problems can easily arise in this stage. if the dry ingredients are not completely incorporated at this stage, they will never be completely incorporated. Once you begin to heat the pudding with unincorporated starch, the outside of the starch granules will absorb water and turn the starch into very firm lumps in the pudding. These have always reminded me of tapioca, which is actually made by a similar process.
If you experience this problem, it means that you mixed in the milk too quickly.
Process: Premix the Egg Yolks
By premixing the egg yolks, we are able to break down the natural connections that exist within each yolk. This makes them much easier to mix into the solution later. Again, the more mixing we can accomplish at a high viscosity, with high sheer, the less likely we are to have problems with integration.
Process: Cook the Pudding
The cooking step has two functions: it thickens the pudding and changes the flavor.
The "cooking" step of making pudding acts to hydrate the starch and change the proteins in the egg yolks. When hydrated, the long starch molecules (from amylose) stretch out into a helical shape, forming a loose net-like structure through the pudding. It is the interaction of these molecules that is primarily responsible for thickening our pudding.
The heating effect on the egg yolks denatures the proteins, also elongating these molecules. Due to the presence of amylose and salt in our mixture, the denaturation and thickening of the egg proteins, which would typically occur around 140°F, happens at a much higher temperature, allowing us to heat the mixture to boiling without the egg curdling and separating. The weakening of bonds between the egg protein results in a nice soft texture in our finished protein, which wouldn't be possible without the salt, milk minerals, and protective characteristics of corn starch.
Flavor is also impacted by the cooking process. The milk components contribute a cooked milk flavor to the finished product.
The cooking step is the stage that is most likely to cause problems with pudding. If the pudding isn't continuously stirred during this step, you can scorch the pudding mixture onto the bottom of the pan. While scorched pudding does actually mean it has burned, it can lead to lumpy pudding. This occurs because as a layer sticks to the bottom of the pan, and gets heated faster than the surrounding pudding, it begins to set faster than the rest of the pudding. Once this occurs, it is impossible to mix it back in with the rest of the pudding, causing lumps.
If you experience this problem, turn down the heat or stir faster.
Process: Add the Butter, Chocolate, and Vanilla Last
There are two reasons that we wait until the end of the cooking process to add in the butter, chocolate, and vanilla.
The first is to help keep as many aromatics in the finished pudding as possible. Aromatics, by nature, must be volatile for us to smell them. This means that a cooking process will liberate many of these compounds into our homes and noses prematurely. Adding the aromatics as the last step ensures that you get the most of their wonderful aromas in the finished pudding.
The second reason for adding high-fat items at the end of the cooking is that it helps to slightly disrupt the thickening caused by our hydrocolloids and egg. This means that the pudding will still set properly but become more tender and less rubbery.
Process: Strain the Pudding
Straining allows us to trap any stray lumps that might be left over from the egg, corn starch, or poor stirring during the thickening. If you are anything like me, there will be a few.
Process: Refrigerate Until Set
As we all know, cooling the pudding creates a much firmer pudding. This occurs for a couple of reasons.
The first reason that the pudding sets with refrigeration has to do with the internal energy of the pudding. Simply put, hot molecules move a lot more than cold molecules. As amylose molecules slow down, they begin to spend enough time touching other amylose molecules to form strong bonds with them. These bonds result in a firmer pudding.
The other reason why puddings set after they are cooled is due to a phase change. The fats in our pudding are all melted during the cooking process. These fats, whether dairy or chocolate, are liquid above about 100°F. When we cook our pudding the fats melt—and as we cool the pudding, they will slowly resolidify.
I hope you've enjoyed learning a bit about the science behind making pudding. Cheers, and remember, there's always room for pudding!