The term “cake” encompasses a wide variety of products, differing in formulation and preparation, but all based on the creation of a batter with incorporated air, followed by baking. During baking, the batter expands either due to the increased volume of trapped air as the temperature rises or through the action of a leavening agent, and in some cases, yeast. To better understand the final quality of cakes and optimize production methods, we can categorize them into two main groups.

The first group consists of fat-based sponge cakes, whose structure derives from the creation of a good fat-water emulsion during mixing. The second group comprises foam sponge cakes that depend on the properties of certain egg proteins to trap air. Cakes in the first group often result in denser batters and include pound cakes or muffins. The second group includes fluffier sponge cakes with a higher percentage of air and, therefore, less density, often used for filling with creams or jams.

Key considerations for achieving quality cakes include the type of cake desired, the suitability of the ingredients used, their formulation, the method of mixing and beating the ingredients, and the baking process. In this initial entry on cakes, we will discuss some general concepts that will help us better understand the basics of cake making. We will also delve into the functionality of the main ingredients, although most of them have been previously discussed in the blog. In this entry, we will focus on their role in cake making. Subsequent entries will explore proper formulation, beating methods, and baking of cakes.

Basic Principles

Before delving into the various factors influencing the quality of cakes, it is essential to grasp the phenomena occurring during their preparation. Firstly, it’s crucial to acknowledge that the batter, which eventually transforms into the cake, is a liquid-like product with incorporated air. This air remains trapped in the mixing operation in the form of small bubbles, defined by their radius (r), surface tension (γ), and internal pressure (p). When the bubble size stabilizes, the following relationship holds:

p = 2 * γ/r

Therefore, ingredients that reduce surface tension, such as emulsifiers and some soluble proteins, aid in bubble formation during mixing. As we’ll see later, they contribute to producing cakes with a finer and more homogeneous structure. Hence, the inclusion of an emulsifying substance is advisable in certain formulations. This is also why small-sized components can enhance cake quality by stabilizing bubbles through a phenomenon called Pickering. For a deeper understanding of cakes, studying emulsions and foams is recommended.

In contrast to bread, the quality of flour proteins is not crucial in these preparations. As a liquid batter baked rapidly, there is no significant friction or mechanical work to develop gluten networks. This allows for the production of high-quality gluten-free sponge cakes. Only in special formulations, where the batter is thicker, might some gluten network development occur. However, wheat proteins, while not critical for volume expansion, play a role in the final texture by coagulating during baking, contributing to crumb cohesion. Therefore, in gluten-free sponge cakes, the quantity of egg or egg protein is often increased to fulfill a similar role.

Moving back to foams, smaller bubble radii correspond to higher internal pressures. In extreme cases, with a radius approaching zero (no bubble exists), the internal pressure becomes infinite. As a result, in subsequent processes after mixing, no new bubbles form, and any generated gas, either from a leavening agent or less commonly from yeast, incorporates into the existing bubbles formed during mixing. This underscores the importance of establishing a good structure from the beginning. A structure with fewer bubbles will concentrate all the gas in them, resulting in open and less stable textures. Conversely, a higher number of bubbles ensures a more even distribution of the generated gas, producing cakes with finer and more uniform textures.

It’s crucial to note that between two bubbles of different sizes, the smaller one will have higher internal pressure. Therefore, if these bubbles are close, gas tends to slowly move from the smaller to the larger bubble, eventually forming a single bubble. This phenomenon is known as coalescence. The speed of bubble movement will depend on the radius of the bubble and the viscosity of the medium and is governed by the following equation:

v = 2 * g * r² * (ro – ro₁) / (9 * m)

where g is the gravitational constant, r is the bubble radius, ro is the density of the whipped medium, ro1 is the density of the occluded air and m is the viscosity of the batter.

Consequently, less viscous batters are less stable over time, and larger bubble sizes can lead to similar outcomes. This aligns with the fact that if the batter is not baked within a reasonable time, the resulting cakes are defective, with some bubbles merging, creating a more open and irregular crumb, while others escape to the surface, resulting in a loss of volume in the final cake. Bubbles distant from the surface can even create tunnels inside the cake. As seen, these phenomena are minimized in batters with higher viscosity and smaller bubble sizes. Thus, more critical than batter density, and hence enclosed air volume, is the distribution of these bubbles and their size.

A critical size (θ), depending on the medium’s viscosity, exists above which the bubble can rise to the surface and escape from the batter. It’s important to consider that this phenomenon can occur during batter resting or in the early stages of baking. Therefore, understanding how batter viscosity evolves with temperature, typically decreasing as temperature rises, becomes valuable. As mentioned, no new bubbles are created during baking, and both CO₂ and water vapor formed incorporate into the existing bubbles. In the initial baking stages, the bubbles may enlarge, reaching the critical size and starting to escape from the batter. This underscores the need to achieve good air dispersion during mixing, creating numerous small bubbles to reduce their mobility and yield a finer and more voluminous cake. In an ideal situation, the volume of bubbles in the final sponge cake will be between 3 and 5 times the enclosed volume in the batter, although some gas loss during processing is inevitable.

Reducing surface tension explains why the addition of emulsifiers enhances cake quality, resulting in products with greater volume and a finer crumb. This is particularly important in formulations that create high surface tension. In some cases, adding an emulsifier or emulsified fat is necessary to carry out one-phase mixing. The presence of polyvalent cations, such as Ca²⁺ or Al³⁺, in leavening agents, particularly in their acidic component, can also enhance cake quality by stabilizing protein films at the air/water interface and improving bubble stability.

Low batter temperature, especially in delicate or unstable formulations, can also help increase volume by raising batter viscosity. Similarly, fast baking, preventing coalescence phenomena, is crucial. These coalescence phenomena are also responsible for the shelf life of frozen batter. Depending on the storage temperature, coalescence phenomena occur at different rates in frozen batters. Although the phenomenon is slow in frozen batter, considering the long shelf life of frozen products for months, it can impact bubble distribution and batter development during baking.

In the next post we will talk about the role of the different ingredients in cake making.