Chiffon cake, a quintessential American cake, yet so hard to perfect! One mistake and the whole thing easily caves into itself. How can we keep our cakes airy and elevated? Well, there are several different factors, but it all comes down to one key ingredient - cream of tartar. Let's learn the science of how cream of tartar works in chiffon cake to create the perfect fluffy cake!
Background
Chiffon cake is a light cake defined by two characteristics. First, it uses vegetable oil instead of butter, the fat usually used in traditional cake recipes, so it's light but still retains moisture. This trait also makes it better-suited for fillings or frostings with ingredients that need to be refrigerated or frozen. Second, a chiffon cake is a cross between a high ratio cake and a sponge cake. It combines the richness of high ratio cake from the batter and the lightness of sponge cake from the meringue, or whipped egg whites and sugar. Chiffon cake, along with angel food cakes and sponge cakes, is considered a foam cake because it is leavened naturally from the meringue, and not from chemical leaveners such as baking soda and baking powder. Chiffon cake pairs really well with fruit or a light cream, but also flavors like chocolate or matcha.
When I made chiffon cake for the first time, it completely deflated! Although it still tasted pretty good (thankfully), it was only half its original height and a bit denser in texture. I was sure I followed the recipe to a tee each time, yet I continued to have failures. I wanted to get to the root of the problem and find out how I could create the perfect fluffy cake. After showing the procedure on how to bake the most basic chiffon cake, let's look at the science to see break down how chiffon cake is leavened and see what I could do next time!
Procedure
Chiffon cake is a bit harder than other cakes because the egg whites and egg yolk need to be prepared separately. However, it's definitely worth the time and effort if you're going for a lighter and healthier cake! For my specific recipe with servings and measurements click here.
I started by preheating my oven and setting aside my 8-inch chiffon cake pan. I did NOT grease the insides of the pan because the cake needs to cling on the sides for support when it rises (important to get that height!). I prepared 2 bowls without any water or grease, separating the egg yolks into one bowl and the egg whites into the other, and making sure there were no egg yolks at all in the egg white bowl (also very important). In another bowl, I sifted flour into vegetable oil and mixed well until there were no extra flour lumps. I added the egg yolks, vanilla extract, and milk and gently mixed until they were all well-incorporated.
In the large bowl with the egg whites, I added 1/3 of the sugar and cream of tartar. I beat the egg whites with an electric whisk and continued to add sugar at intervals. I beat the egg whites until stiff peaks formed. I combined the two mixtures by transferring the egg white mixture into the egg yolk mixture in 3 parts and folding the mixture in gently. I poured the combined cake batter into the chiffon cake pan and shook the pan to remove any big bubbles. I baked it for approximately 35 minutes and flipped the pan to cool upside down once out of the oven.
As I flipped the cake pan back over after cooling for about 30 minutes, it seemed to have deflated immensely from when I first took it out of the oven. It still tasted relatively light with a hint of sweetness and eggs (and paired very well with some whipped cream frosting), but it was now a much smaller cake. I wondered how I could fix these problems with science!
Science!
Chiffon cakes are usually made from vegetable oil, eggs, sugar, cake flour, cream of tartar, and flavorings. Let's first look at the role of the important ingredients to see how they might affect the final fluffiness and elevation of the cake!
Vegetable Oil:
Chiffon cake uses vegetable oil, which is difficult to incorporate air into. Thus, rather than creaming the fat and sugar together (like most recipes with butter), chiffon cake creams the eggs and sugar together instead. A batter containing flour, egg yolk, oil, and flavorings is made to be later folded into the egg white foam. Additionally, since the vegetable oil is still liquid (it has a low melting point) - rather than a solid like butter - at cooler temperatures, chiffon cake does not tend to harden or dry out as traditional butter cake. The vegetable oil works by coating the starch and protein of the flour with an oily film, reducing the formation of tough gluten (important for soft cakes!). It seems that vegetable oil has more to do with the texture of the cake, rather than immediate fluffiness, but it's great at making our cake moist and tender!
Cake Flour:
Some cake recipes call for cake or pastry flour. This is a flour that is grown especially to have a low-protein content of around 9%, which is also what leads to low gluten content, as well as a more fluffy and tender cake. This is important, as compared to bread, we don't want chewy cakes! Pastry flour actually has an even lower protein content than cake flour, around 8%, and is mostly used to make pie crusts, biscuits, or anything where you want a tender, crumbly, or flaky texture.
Flour also provides the main structure within the cake. The starch in the flour stiffens and helps strengthen the egg foam. Additionally, some of the proteins in the flour join together to create an extensive network of proteins called gluten, which holds the cake together. Although (as previously mentioned) we don't want too much of a gluten network to form to prevent a thick/chewy cake, this network is still important so the cake doesn't collapse completely. The gentle folding used to incorporate the flour mixture into the egg white mixture also reduces gluten formation, so it's important not to over-beat our cakes! The gluten network's elastic properties allows the batter to expand during baking by incorporating gases and later solidify to support the heavier sugar and other ingredients. Thus, the specific type of flour used in chiffon cake is important to keep that light, fluffy texture rather than heavy or chewy, but gluten network formation is still needed to keep that structure elevated. One possible ingredient to strengthen the gluten network is salt!
Eggs:
First, it is important to beat the egg white foam very stiff because it also helps provide structure for the cake. Our beaten egg whites can increase in volume 6-8 times! They supply the majority of those air bubbles from beating the egg whites and sugar together, and these air bubbles later expand while baking. The egg proteins coagulate to form a rigid wall around the air bubbles, preventing them from bursting and causing the cake to deflate. The gentle folding mentioned earlier in the cake flour section is important here as well, as it prevents breaking the bubbles formed during whisking.
More specifically, egg whites are able to foam due to two egg white proteins, albumin and ovalbumin. The beaten albumin proteins are what bond together to form a fragile network that holds all the tiny air bubbles in place. first, egg whites are 90 percent water and 10 percent protein. The proteins denature (the coiled amino-acid chains unfurl) when beaten, and they align themselves between the air bubbles and the water molecules, reinforcing the air bubbles’ walls. The longer the egg whites are whipped, the more tightly the albumen proteins cluster together to form the structure. If whipped too long, however, they eventually force water out of the foam structure, which destabilizes and separates into a dry lather and a layer of liquid, and causing the foam to deflate as air escapes. This can happen in the oven as the cake loses moisture, resulting in a sunken cake. Ovalbumin does not play an important role when the egg whites are beaten, but it does coagulate when heated, forming its own network and making it resistant to collapse as the water from the egg whites evaporate in the oven.
As mentioned in the procedure, it's VERY important that the bowl and all utensils which come in contact with egg whites are clean and free of grease. Any fats in the grease will destroy the egg white foam by interfering with the protein bonds of the egg whites. The egg whites also cannot come in contact with the egg yolks, as the yolks contain a fatty substance that destroys the egg white's ability to foam. The oven temperature should not be too low, otherwise then the batter will set too slowly, and expanding gas bubbles will coagulate to produce a heavy texture, making the upper surface sink. Thus, egg whites are essential to elevate a chiffon cake - it's important to beat the egg white foam stiff, but fold it gently into the egg yolk batter so the foam air bubbles aren't destroyed.
Cream of Tartar:
How can we help keep that fragile egg white foam network from falling apart? That's where cream of tartar comes in! This ingredient makes the mixture more acidic, which is also favorable for protein bonds. It's chemical name is potassium bitartrate or potassium hydrogen tartrate, and it is a by-product from making wine as a crystallized precipitate in wine barrels after the grape juice has fermented. It is often used as a leavener with baking soda or as a baking powder substitute, or to stabilize whipped cream!
In the case of chiffon cake, cream of tartar is added to egg whites during the whisking to boost the volume by enhancing the formation of air bubbles and stabilizing them, allowing them to retain water and air. It also increases the eggs’ tolerance to high temperatures, making sure the cake keeps its height even after baking in the oven. How does it work? The acidic nature of cream of tartar lowers the pH of the albumin, which changes the electrical charge of the proteins (free H+ ions can bond with negatively charged groups, disrupting ionic bonding between charged side chains of amino acids) and makes them more sensitive to denaturation. This causes the egg whites to foam much sooner. Cream of tartar also prevents the newly coagulated proteins from packing too tightly, reducing the likelihood of overbeating the egg whites, so the structure keeps the water and air bubbles in place and is more secure. Preventing the proteins from clustering too much also means the egg white foam is elastic in nature. The protein structure stretches to its thinnest during baking, and the abundant, evenly-distributed air bubbles within this structure results in tall yet tender-crumbed cakes.
Because the main idea is that cream of tartar adds acidity, substitutes such as lemon juice or vinegar can be added. However, the appearance and taste may vary with these ingredients. For example, lemon juice might be better for a fruit-flavored cake. These other options are also effective than cream of tartar, as they are liquids that dilute the egg white and interfere with the stabilizing action of the acid. Also, while cream of tartar is 100 percent acid, lemon juice is only 3 percent acid, so it’s less potent.
Conclusion
It seems like there's a lot to keep track of when making chiffon cake! I have learned that using cake flour and cream of tartar are essential ingredients for an elevated cake, but whipping egg whites to perfect stiff peaks is also a crucial part. Vegetable oil ties it all together by keeping our cake moist and tender for a long time. It would be interesting to try out the cream of tartar substituents as future experiments, and see how they affect the final cake as well. Hopefully, breaking it down to the important ingredients helps you better understand how chiffon cakes are made through science, so that you can make perfect fluffy-as-air cakes too!
Link to my chiffon cake recipe.
Link to my post on the history & culture of chiffon cake.
Want to Learn More? (always cite your sources, kids)
https://www.thespruceeats.com/cake-ingredient-science-481230
https://www.mygreatrecipes.com/blog/incredible-cream-tartar-use-substitute/
https://slate.com/culture/2013/11/what-is-cream-of-tartar-the-food-explainer-explains.html
https://www.theguardian.com/science/blog/2010/jun/09/science-cake-baking-andy-connelly
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