1001 Tips for Making Your Own Wedding or Celebration Cake
Part 2 – The Science of Ingredients
This is Part 2 of my attempt at providing 1001 Tips for Making Your Own Wedding or Celebration Cake.
Part 1 dealt with the Design & Planning stage, and this part deals with… drum roll please….
Have you ever wondered why some recipes call for All Purpose Flour and some want Cake Flour?
Have you ever wondered why you cream together the butter and sugar?
Have you ever wondered why, Why, WHY did the center of my cake collapse!!
If you have those kinds of questions then keep reading. This post tries to explain the chemical reactions that take place between the ingredients, and hopefully my rambling might explain the when, where, and why things can go wrong. So hang onto your hat and start channeling your inner Alton Brown, this post is about to get a little science-y.
The Chemistry of Cakes – it is all about the Gluten
Big Tip #1 - Don’t try and tweak a cake recipe too much
A cake recipe is a precise chemical formula. It is a choreographed dance between flour, sugar, eggs, liquid, and fat. Tweaking or changing an ingredient in a cake recipe can produce a tasty surprise or a stunning flop. If you are going to bake from scratch you should know a little about the dancers that are performing your mixing bowl:
- Structure Builders / Tougheners – Flour (gluten & starch), Eggs, and Cocoa Powder - These are the structure builders in cakes. Think of them as a skeleton. They give a cake both structure and strength, which in turn allows the cake to hold the new, larger shape produced as gases inside the batter expand during baking.
- Too little in the way of structure and the cake will collapse as it cools.
- Too much structure and the cake will be tough and unpleasant to chew.
- In today’s world everyone knows about gluten, but did you know that dry flour doesn’t contain gluten? Flour has two proteins (glutenin & gliadin) that join together to form gluten only when the flour is hydrated (ie exposed to water). Water turns the flour proteins into a flexible web of interlocking gluten fibers. The more water you add, the more structure will form, and consequently the tougher the cake will become.
- Physically stirring the batter accelerates the formation of the gluten web, so the more you mix the batter, the stronger the gluten web becomes which again toughens the cake. This is why that box cake mix tells you to only mix for 2 minutes, and the brownie mix says to stir for 50 strokes. They don't want you to overdevelop the gluten and end up with a tough brownie or cake.
- The starches in flour also form structure when exposed to water, and
- Egg proteins coagulate and form structure when exposed to heat.
- Tenderizers – Sugar, Fats (butter, shortening, lard), Oil, Baking Powder – Tenderizers are ingredients in the cake that interfere with the structure builders (aka gluten, starch, and egg proteins).
- Fats and oil surround the flour proteins which prevent them from absorbing water and turning into gluten. In essence the fats waterproof the flour proteins. If gluten and structure can't form, the cake will be tender. Thus the fat tenderizes the cake by limiting the size of the gluten web that forms.
- Sugar is highly hygroscopic which means it absorbs water like a dry sponge. If the sugar traps some of the water then there isn't as much around to convert flour proteins to gluten. So like the fat, the sugar tenderizes the cake by limiting the amount of water available for gluten formation.
- But like any good thing, tenderizing can be taken too far. If the fat and sugar stops all gluten formation, then the cake will collapse under its own weight. The ratio of structure builders to tenderizers is a delicate balance. You want enough tenderizers so the cake is soft and easy to chew, but not too much or the cake will collapse due to lack of structure.
- Moisteners – Water, Milk (and milk products), Egg, Butter, Oil – All of these ingredients (except the oil) add moisture to the cake through water, and water has an extremely critical role in the cake making process.
- Water dissolves and hydrates many of the other ingredients in the batter.
- Do you know that whole milk is 88% water, eggs are 75% water, and sour cream is 71% water?
- Water sticks to and dissolves the sugar,
- Water activates the baking powder,
- Water hydrates the gluten in flour and allows it to form structures.
- Too much water will encourage excess gluten development which will toughen the cake.
- Too little water will keep the flour from hydrating and also keep the sugar from dissolving. Both of these conditions will cause the cake to sink when removed from the oven.
- Any sugar crystals left undissolved by water will also form a sugary crust and excess browning on a cake. This is fine, and even encouraged, in pound cakes, but not something you want in a white wedding cake.
- Oil is the only moistener that contains no water. Instead oil moistens because the fat is a liquid at room temperature.
- Oil is a superior moistener than water because any water not tightly bound to sugar, gluten and starch is turned into steam and escapes during baking.
- Driers – Flour, Corn Starch, Sugar, Cocoa Powder – These ingredients absorb moisture and pull it out of the cake. Flour needs to absorb moisture to generate gluten strands and structure, and sugar needs moisture to dissolve. If the recipe has too much in the way of “Driers” and not enough “Moisteners”, the cake will be dry, sunken, with sugary, brown crust.
- Leavening Agents – Baking Powder, Baking Soda, Whipped Egg Whites – These ingredients help the cake to rise. As heat and chemical reactions cause the gasses to expand, they lift and lighten the cake.
- Notice that some ingredients are in two categories. Flour is both a structure builder and a drier. Oil is both a tenderizer and a moistener. Egg White is both a structure builder and a leavening agent. It is this complex relationship of ingredients that makes scratch cake baking and recipe development both troublesome and rewarding.
More About Flour
- Un-sifted flour can destroy your scratch cake – no really, it can!!! Do you get inconsistent results when you bake from scratch? The culprit may be the flour and how you are measuring it.
- Home cooks in the US use volumetric measurement; we use measuring cups and spoons for both liquid and dry ingredients. This is a problem when measuring flour because flour settles; it becomes denser and more compact over time. Think of flour like a balloon. When the balloon is full of air it is plump and round and probably as big as your head, but without the air it is as flat as a pancake. The balloon itself weighs the same regardless of its fullness or size. Same with flour. As the milling air originally trapped between the particles of flour escapes, the volume of flour gets smaller and smaller. If you fill a cup with sifted flour and let it sit for a month, you may find that you only have 7/8; after 3 months you might have 3/4s of a cup!
- If your scratch cake flopped, it may be because you unknowingly added too much flour.
- Ideally you should weigh your flour. Weight is a better way of getting consistent results cake after cake.
- But most recipes don’t give you the weight of the flour, and even if they did it wouldn't be completely accurate because different flours have different densities and weights. For example, for Swans Down Cake Flour one cup of sifted flour weighs 120 grams, but one cup of sifted Martha White Bleached flour weighs 140 grams.
- So what is a home baker to do? Well the only way to insure you are using the appropriate amount of flour is to SIFT THE FLOUR BEFORE YOU MEASURE. When you sift, you reintroduce air into the flour and this will give you a more reproducible measurement.
- If you don’t sift, you don’t know how much the flour has compacted and how much flour you are actually putting in your cake batter.
- One trick I have started using is when I open a new bag of flour I sift and weigh one cup of flour. I then write this number on the packaging. From then on I can just weigh out the amount of flour I need without bothering to sift before I measure. Of course I still need to whisk and sift the flour when I add the baking powder and salt, but this trick eliminates one step!
- The wrong flour can destroy your cake - Okay, that may be an exaggeration, but the wrong flour can really change the taste and texture of your cake. The two main types of flour used in cake baking are Cake Flour and All Purpose Flour.
- What in the heck is Cake Flour?
- Cake Flour is milled from soft red winter wheat or soft white wheat. It uses the absolute heart of the endosperm (essentially free of bran and germ) which give the flour a finer grain, whiter color, lower protein content (6-8%), and slightly higher starch content.
- Protein is used in gluten formation. So the lower protein content in Cake Flour means less gluten development, and less gluten development results in a tender cake with a higher volume.
- Cake Flour is bleached with both chlorine gas and benzoyl peroxide.
- The chlorine treatment does a lot:
- The chlorine treatment weakens the gluten structure, and makes it easier to break under the pressure of expanding leavening gasses.
- The chlorine treatment alters the starch molecules in the flour which allows the starch to absorb more water. With less free water in the batter, the batter thickens and can trap more tiny air bubbles during mixing. The bubbles are important because they defines the "crumb" of the cake. Air bubbles also provides the cavities where all the powerful leavening gases accumulate before they start to lift the cake.
- The chlorine treatment also lowers the pH of the flour which reduces browning of the cake.
- The benzoyl peroxide treatment makes the flour a bright white color.
- The chlorine and benzoyl peroxide treatments alter the taste of the flour too.
- Because of the unique properties of Cake Flour, it is typically used in High-Ratio cakes. A High-Ratio Cake has a high ratio of liquid and sugar to flour (it has more tenderizers than structure builders). Without Cake Flour, a High-Ratio Cake would likely rise and then collapse during baking and cooling.
- Some say you can "make" cake flour by adding corn starch to flour, but that doesn't really work. The added corn starch may dilute the overall protein content and increase the amount of starch, but it doesn't add any of the chlorine gas effects.
- Interesting note: flour bleaching agents are banned in EU and UK so no Cake Flour for them.
- All Purpose Flours - How many brands of All Purpose (AP) flour can you name? 5? 10? 15?
- Do you know that each brand of flour has a different protein content (usually in the range of 9-12%)?
- Some brands are a mixture of soft and hard wheat, some are just soft wheat, and some are just hard. Generally the harder the wheat, the higher the protein content.
- The brand of flour you select will alter the taste, texture and crumb of the cake depending on how much protein that particular flour contains. For example, White Lily AP is made from soft winter wheat and has a protein content of 9%. Martha White also has approximately 9%. Gold Medal and Pillsbury have 9-10%. King Arthur Unbleached AP has 11.7%.
- So if your cake recipe calls for All Purpose flour, try to use a flour with the lowest protein content you can find. The flour you use WILL impact the texture of the final cake.
Sugar, Sugar, Sugar
The main purpose of sugar in cakes is for sweetness, but sugar also has other important functions:
- Sugar is highly hygroscopic meaning that it attracts and binds to water. If the water binds to the sugar there is less water available to convert the flour proteins to gluten.
- Sugar is considered a tenderizer because it inhibits the formation of structure building gluten. The more sugar added, the more tender the cake. But too much sugar will stop all gluten development which will ultimately cause the cake to collapse.
- Sugar contributes to browning through the process of caramelization and Maillard browning. Caramelization is the simple browning of sugar, but the Maillard browning reaction requires the presence of both sugar and milk proteins.
- Because of Maillard browning, cakes with milk (vs water) are more prone to browning. A nice sugary brown crust is treasured in pound cakes, but not good for a white wedding cakes.
- To reduce browning an acid can be added to lower the pH of the batter. Common cake acids include Cream of Tarter, vinegar, buttermilk, lemon juice, etc.
- To increase browning (for pound cakes) raise the pH by adding an alkali like baking soda.
- Sugar acts as a leavening agent because air gets trapped around the irregularly shaped sugar crystals. The process of creaming fats with sugar also introduces air into the mixture. (see more on leavening below)
- Sugar stabilizes whipped egg whites. The sugar keeps the egg whites from collapsing and losing the air that was carefully whipped into the whites. Sugar also stabilizes beaten whole egg that are used in chiffon cakes, and egg yolks that are used in custards.
- Sugar increases the temperature at which eggs whites coagulate or set which allows more time for the cake to rise. Once the eggs whites coagulate, the cake can no longer rise.
- When used in small amounts, sugar promotes microbial growth, but when used in high enough quantities it inhibits microbial growth. This is why high sugar frostings and icings that contain dairy products (milk, cream, cream cheese) don't require refrigeration. (Note: different States have different rules on refrigeration requirements of cream cheese frosting. Check with your State to be sure.)
Types of Sweeteners:
- Granulated sugar is the most common sugar used in baking. It is made from either sugar cane or sugar beet.
- Powdered sugar is pulverized granulated sugar with about 3% added cornstarch that keeps it from clumping. (Remember that sugar is hygroscopic and will even absorb moisture from the air. The corn starch stops this absorption.) Powdered sugar is about 10 times as fine as granulated sugar. It is commonly called 10X sugar. Powdered sugar is typically used in frosting rather than cake batters.
- Fondant sugar is an extremely fine powdered sugar. Fondant sugar is 100 times finer than powdered sugar and contains no corn starch. As the name implies it is used to make fondant.
- Brown sugar is granulated sugar with about 10% added molasses.
- Simple Syrups are made by mixing equal parts liquid and granulated sugar and then heating till the sugar is dissolved and the liquid is reduced.
- Glucose Corn Syrup is a clear syrup produced from the breakdown of starch molecules. Corn Syrup isn't as sweet as granulated sugar, but it does act like sugar (tenderizes, moistens, browns). Corn Syrup is used to thicken products and prevent the recrystallization of granulated sugar. Corn Syrup can also be added to cake batters to tenderize (inhibit gluten production) without making the cake as sweet as granulated sugar. Corn Syrup is added to glazes and icings to make them flow better, add a glossy sheen, and add bulk without making them overly sweet.
If a recipe calls for whole milk, can you substitute 2%, skim, or even water? If a recipe calls for water, can you substitute milk? Well, the answer is yes and no. Whole milk is 88% water so the substitution probably won’t drastically impact the overall structure of the cake, but it might affect the look and taste. In addition to water, whole milk contains about 5.0% Lactose, 3.5% Milk Fat, and 3.5% Protein. The 12% of milk that is not water is know as the Dry Milk Solids (DMS).
The primary purpose of the milk (and milk products like sour cream, buttermilk, etc) is to add moisture (water) and moistness (a liquid sensation in the mouth) to the cake. Remember that moisture (water) is necessary for the formation of gluten and for the hydration of starch and sugar. But the milk solids in milk products serve other purposes as well:
- The solids in milk causes browning of a cake. The combination of milk protein and sugar are the basis for the Maillard reaction which gives baked items their golden brown crust. To reduce the amount of browning on a cake you can lower the baking temperature or add an acid like Cream of Tarter, vinegar, or lemon juice.
- Milk products delays staling in baked goods.
- Milk gives a richness of flavor and helps blend flavors.
- Milk firms up the cake crumb making it more resilient and easier to handle.
- Milk products also strengthens the cell structure of egg whites keeping them from stretching and breaking during baking.
- Powdered whole milk added during the creaming of fats and sugar will helps trap more air into the mixture. Trapping more air will produce a finer cake crumb.
- Milk solids also stabilize the creamed mixture of fat and sugar. The milk solids include emulsifiers that keep the fats and water bound together. Without the emulsifiers the fats and water may "break" or separate.
What’s your favorite FAT?
Cakes can be made with different fats including butter, margarine, lard, shortening, and oil. Each will give their own unique texture and flavor to the cake, but all are used to tenderize a cake.
So is one fat better than the other? Some people think that cakes made with butter are the best, but does the science backup that thinking?
- Butter is by far is the best tasting of the fats. Nothing is better for flavor and mouthfeel, but butter is expensive.
- Butter is not very healthy because it is high in saturated fat (more than lard) and cholesterol,
- And because of its low melting point, butter it is not the best option for getting fluffy cakes with a lot of volume and a fine crumb.
- Butter is more suited for dense cakes rather than light, fluffy cake.
- If a recipe doesn't indicate which type, then always use unsalted butter. Different brands of butter will have different amounts of salt, so if you use salted butter you are never sure how much salt you are actually putting in the cake.
- Don't use salted butter in buttercream, it is just too much salt for frosting.
- In the US butter has a minimum of 80% butterfat. The rest is typically water (16%) and milk solids (4%).
- To make a moist cake you need a lot of liquid. You also need this liquid to stay in the cake during baking and not turn to steam and escape. Shortening does a better job of trapping moisture and air than butter, so a cake made with butter will be drier than the same cake made with shortening.
- Lard is another fat, but because of its crystalline structure it is not suited for fine-crumbed cakes. Lard is used mostly for pie crusts.
- Margarine is imitation butter. It has a similar composition of butter (80% fat and 16% water), and is healthier and cheaper. But margarine doesn’t have the same pleasant mouthfeel as butter and tends to leave an oily or greasy feel to the mouth.
- Shortening is the same as margarine minus the water.
- Because shortening can trap and retain more air and liquid, a cake made with shortening will be moister than the same cake made with butter.
- Common grocery store brands are considered "All Purpose Shortening". They can be used in everything from cakes to a deep fryer.
- You can also buy High-Ratio shortening that has added emulsifiers which helps the shortening trap and holds more air and liquid. This makes it well suited for both cakes and frostings. The High-Ratio shortening makes frostings creamier and fluffier, and makes cakes that are moister and more tender. Opt for the High-Ratio shortening if you can find it.
Eggs, like flour, are structure builders. Eggs are actually just as important as gluten for building a well structured cake.
- Heat from baking interacts with the protein in eggs and cause them to coagulate and form a network of interconnected strands of protein.
- Without eggs, most cakes would collapse.
- Use fresh eggs - Fresh eggs will whip up lighter and fuller than older eggs. Fresh eggs are also slightly acidic which helps stabilize the egg proteins which part of the cake's structure builders. As an egg ages it slowly becomes more alkaline which make the protein strands less stable.
- Whipped egg whites are excellent at trapping air because egg whites can expand up to 8 times their volume during whipping. Air bubbles in the batter are essential part of leavening. (see section on leavening below.)
- But make sure you don’t over whip your egg whites. Over whipping will stretch and thin the cell wall of the proteins, and during baking these thin cell walls will break and collapse.
- Sugar helps to stabilize whipped egg whites and keeps them from collapsing or weeping.
- Egg yolks contain a natural emulsifier that helps keep fat and water from separating. Because of this emulsifier, eggs are often added to creamed butter or shortening to keep the mixture stable. The emulsifiers in egg yolks help bind together ingredients (water and fat) that would normally repel each other.
- But make sure you follow the recipe directions and only add one egg at a time!!! And make sure you fully incorporate each individual egg into the fat before adding the next egg!!! And don't use cold eggs. Adding cold eggs or adding the eggs too fast will cause the emulsion to “break”. When the emulsion breaks, the water in the egg will separate from the fats and they can never be rejoined.
- When the emulsion "breaks", the mixture will look curdled.
- Once the emulsion “breaks”, it is broken for good. Adding additional ingredients like flour may make it look like the water and fats are once again bound, but they are not. A poorly emulsified cake will not rise properly and will have a coarse, hole-ridden crumb.
- Despite the fact that eggs are 75% water, too many eggs will make a cake dry. Remember that the protein in eggs builds structure, and the additional structure will dry out the cake. The water in the eggs will convert to steam and escape during baking. This steam will lift the cake and cause it to rise, but it will also dry out the cake. This is why adding an extra egg to a brownie mix will change them from dense, moist and fudgy to lighter, cake-like, and drier.
- Over whipping egg whites will also dry out a cake. If the recipe calls for egg whites whipped to soft peaks, stop at soft peaks and don’t over whip to stiff peaks.
How to get your cake HIGH...
Cakes are light and porous because gases trapped inside the batter expand (due to heat and chemical reaction) and stretch the flexible cell walls of the gluten, starches, and egg proteins. This process of gas expansion is called leavening. Leavening is what gets your cake high.
There are three types of leavening gases in cakes: steam, air, and carbon dioxide.
- Steam is created when the water in the batter is heated beyond the boiling point. Water expands to over 1600 times its volume when it goes from a liquid to a solid state, so water and the resulting steam is a major leavening gas in cakes.
- Carbon dioxide is created when Baking Soda comes in contact with an acid like vinegar, lemon juice, buttermilk, etc.
- Baking Powder is a mixture of Baking Soda and a dried acid like Cream of Tarter. When the baking powder comes in contact with water the water hydrates the dried acid which in turn reacts with the baking soda in the baking powder mix to produce carbon dioxide.
- Most baking powders are Double Acting, so carbon dioxide is first activated when the baking powder come in contact with water and then again when it is heated.
- Check the date on your baking powder – make sure it isn’t expired or close to it.
- Once a container is open, high humidity can also weaken the baking power.
- To test the effectiveness of the baking powder, place 1/2 teaspoon of baking powder in bowl and pour 1/4 cup of boiling water over it. If it starts to bubble violently then it is still good. If it just bubble little, get a new can.
- You don’t want to ruin your cake because of an old baking powder.
- Air is the third leavening agent.
- Air is introduced into the cake batter through physical processes.
- When flour is sifted, air is trapped between the particles and the flour fluffs up. This is another reason to SIFT your flour!
- When sugar is creamed with fat, air gets trapped between the grains of sugar and smears of fat forming tiny air bubbles or pockets.
- When egg whites are mixed, huge amounts of air is introduced which expanding the egg whites 3,4 or 5 times their original volume.
- Even the act of stirring the batter or folding other ingredients into the batter traps air inside the mix.
- Air bubbles / air pockets are very important to the final density, height, and crumb of the cake. The more air pockets trapped in the batter, the finer the texture or crumb of the cake.
- Air pockets are ONLY formed during the mixing process. Once mixing stops, no more air pockets are created.
- Once in the oven, heat causes the air sitting inside the pockets to expands a tiny bit, but the trapped air is not the real magic of the air pockets.
- Instead the real purpose of these air pockets is to give the other gasses a place to collect. As the steam and carbon dioxide form, the gases will collect in all available air pockets. Once inside the air pockets, the steam and carbon dioxide gases start expanding, and expanding, and expanding.
- The expanding gas pushing on the walls of the air pockets, enlarging the size of the bubble and forcing the cake to rise.
- The number and size of the air pockets is very important because they determine the "crumb" of the cake. A large number of small air bubbles will give you a fine crumb, a smaller number of large air bubbles will give you a coarse crumb.
- Without air pockets the gasses have no place to collect. Eventually the gasses will form massive bubbles and tunnel their way to the surface of the cake. Once at the surface they explode like lava erupting from a volcano. If you find worm-like tunnels in your cake it means you didn't mix the batter enough, and not enough air bubbles were formed.
Whoa my fingers are tired, if you made it this far I guess your eyes are tired too. Who knew there was so much chemistry and physics involved in combining Flour, Fat, Sugar, Liquid, and Eggs.
But don't take your Alton Brown hat off just yet -- you will need it for the equally scientific process of Mixing the Batter.
Next up is Part 3 - Oven, Pans, and Pan Prep
PS: If you want to read more about the science of cooking and baking. Try How Baking Works, The Science of Good Cooking, The Baking Bible, or any of the Alton Brown Good Eats books.