- Food and Cooking
Science of Pudding
The science of pudding may have never crossed your mind. But contained within a simple pudding recipe lie 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, and each processing step. By understanding the science behind these recipes we can confidently change recipes that use these ingredients and diagnose any problems that arise. Gone are the days of fearful cooking!
Basic Vanilla and Chocolate Pudding Recipe
This pudding recipe is a simple, no frills attached recipe that I like to use to make a mix of chocolate and vanilla pudding. I usually make the vanilla pudding, pour off half of it, then add the chocolate directly to the pot, stir it to melt the chocolate, then pour off the second half. It is interesting to see the integration of chocolate, and what it does with the texture. I notice that my chocolate pudding is typically smoother, richer, and more consistent. I attribute this to two characteristics in 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.
- 4 & 1/2C milk
- 2/3C table sugar
- 1/4C corn starch
- 6 large egg yolks
- 1/2t salt
- 6T unsalted butter*
- 2t ground vanilla bean
- 3OZ dark chocolate
*Optionally substitute unsalted butter and 3/4C of milk for 1.5C of heavy whipping cream - total milk with substitution is equal to 3 & 3/4C. If using this substitution, add the cream with the eggs before cooking.
Making the Pudding:
- Measure the sugar, corn starch, and salt into a large saucepan
- Slowly whisk the milk into the dry ingredients, adding progressively more milk only once you are sure that the dry ingredients have been well incorporated.
- Whisk the egg yolks until slightly frothy in a bowl, then whisk into the pudding base
- Continue whisking the pudding while heating on the stove 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 the pudding at boiling temperature (but not boiling) until it is sufficiently thickened, and pudding drizzled on the top of the cooking mixture retains a distinct memory.
- Remove from heat and stir in butter and 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
- Stir chocolate into remaining half of mixture, stirring every 30 seconds until completely incorporated
- Strain chocolate pudding through mesh strainer into serving containers on top of vanilla pudding
- Refrigerate until set
this is an essential part of every pudding, and supplies several important characteristics to the finished product. We want it for five components; Water, Sugar (Lactose), Fat, Protein, and Minerals. Good milk should be almost flavorless, but it still excites ones survival instinct by being packed full of the macronutrients that we need to survive. Heating milk generates flavor molecules called lactones. When separated lactones remind us of the aromas 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.
It doesn't make a big difference to purchase whole milk or skim milk, as long as you are adding enough cream, butter, or cocoa fats back to the pudding. Pudding without enough fat will seem flat and boring to eat instead of decadent and indulgent.
Typically the sugar used in pudding is simple table sugar comprised of crystalline sucrose. This is added to the pudding in addition to the 6 to 7% lactose already present in the milk. 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 which 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 sweetness, however each sugar has approximately the same effect per ounce on the water activity, boiling point, and freezing point. This means that use of a different sugar will allow 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.
Egg yolk is commonly added to pudding for several reasons. The first and most obvious impact is the change in color. Egg yolk also contains a good amount of fats, proteins and phospholipids. The egg yolk plays several very important functional roles in the pudding making process. First and foremost, the egg yolk helps to act as a thickener. Egg yolk can yield a very desirable tender creamy custard, but without additional thickeners, such as the commonly used corn starch, 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 amount of yolks for a properly thickened custard without additional thickeners as 3 yolks per cup. This quantity of egg contributes a strong egg flavor, which is not always desirable in puddings. The same characteristics of an egg yolk which make it a weak thickener actually act as emulsifiers as well. It is the presence of lipid bound proteins and phospholipids such as Lecithin which 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
Starch, a type of hydrocolloid thickener, is an extremely common thickener used in everything from pudding to delicious thanksgiving gravy. We all know the terrible results of an attempt to mix it directly into warm gravy, yielding lumpy gelatinous pea sized contaminants, and ruining your thanksgiving feast. Where did all of these "starch rules" come from? Why does there exist such a fear of this simple thickener? An explanation of the mechanism of action of starch will help.
The basic molecular building block of 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 a cation Sodium (Na+). These ions play an important role in so far 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 egg, and helps to ensure that it stays delicate. The obvious function of salt as a flavoring also applies.
Ingredient: Butter Or Cream
Both Butter and Cream are very similar functionally in pudding. They are both added for their fat, which our human bodies identify as delicious, in spite of its lack of flavor contribution. 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 which can be found in movie theater popcorn. The function of both our egg and 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. If using real vanilla bean, a nice flecked appearance is also a result. Vanilla is actually a cured seed pod from an orchid. The growth, harvest, curing, and export of vanilla is a thing of incredible complexity which many people do not consider due to the prevalence of the flavor. The flavor characteristics of vanilla stem from a combination of the raw seed pod and the treatment and curing process which it undergoes. Drastically different flavor profiles can be achieved with different supplies of vanilla.
Chocolate is really an optional ingredient in this pudding recipe. As mentioned in the recipe however, it does act to change the texture and flavor of the finished pudding. I attribute this change to two different characteristics that chocolate has. The first is fat. Chocolate contains a very high amount of cocoa fat, labeled as cocoa butter on the ingredient statement. This is, as I have mentioned before, interpreted as Yummy by our brain. The second important ingredient in my chocolate is lecithin. Lecithin, a general term for phospholipids, is a great emulsifier. I expect that 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. Not all chocolate contains lecithin, so be sure to check the ingredient label if you need it.
Process: Mixing dry ingredients
Mixing the dry ingredients is a good way to break up the sometimes clumpy corn starch. This can help these mix evenly into the milk.
Process: Mixing in milk - slowly
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 which may not otherwise dissolve in the solution.
This is a likely step to cause problems. 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, you mixed in the milk too fast.
Process: pre-mixing the eggs
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.
The "cooking" step of making pudding acts to hydrate the starch and change the proteins in from the egg yolk. 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 140F 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, a result of the generation of
The cooking step is the most likely cause of problems with pudding. If the pudding isn't continuously stirred through this step, you can "scorch" the pudding mixture onto the bottom of the pan. While "scorching" pudding does not lead to burning anything, 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: Melt in Butter, Chocolate, and Vanilla
There are two reasons that this occurs at the end of the cooking process.
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 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 Pudding into final containers
This process is just as it seems, a safety net to capture any mistakenly thickened lumps 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 more firm pudding. This occurs for a couple reasons.
The first reason that the pudding sets with refrigeration comes down to 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 pudding sets harder after it's 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 degrees F. When we cook our pudding they all melt, and as we cool the pudding, they will slowly solidify again.