The Art and Science of Foams

During the COVID-19 pandemic and its eventual lockdown enforced on the world, Dalgona coffee due to social media trends, made its way to every house. The rarely heard name in the Indian households was very casually used. Three simple ingredients instant coffee, water and sugar when whisked together becomes a nice and dense foam. People usually imagine foams being the frothy bubbles, but it is much more than that.

So, what are edible foams, and how do they form?

In simpler words, foams are gas bubbles suspended in either a liquid or solid phase. Gases such as carbon dioxide or air, are incorporated throughout a liquid or solid phase through whipping or blending. As the gas is trapped within the liquid, a foam with a light and airy structure is formed. The amount of gas incorporated into the foam will determine how light it turns out. Foams can have a large volume while remaining extremely light. The liquid phase can be as simple as egg white or complex, with solid matter, ice crystals, and/or emulsified fat droplets. Baked goods are examples of heat-set foams that have a solidified structure (1,3).

Foaming agents are added to stabilize the bubbles and prevent them from collapsing by creating a film around gas bubbles. They have hydrophobic and hydrophilic ends and position themselves between the gas and liquid phases, with the hydrophilic end remaining in the liquid and the hydrophobic end facing the air (or gas bubble). This makes it easier to create foam. The energy applied during whipping is also important, more energy creates smaller bubbles and increases foam volume, as long as enough foaming agent is available to coat and stabilize the bubbles. In food systems, proteins are commonly used. A few examples of foaming agents and stabilizers include gelatin, lecithin, agar-agar, calcium alginate, calcium stearoyl lactylate and xanthan gum, often used in various products (1,5).

Egg Foams

Some of the most common egg foams include meringues, soufflés, and mousses. Egg white consists primarily of about 90% water into which about 10% proteins (including albumins, mucoproteins, and globulins) are dissolved and almost no fat. When eggs are beaten, air is added, and the proteins are denatured. The proteins can bond to one another side-to-side as crosslinks which add to the stability of a foam.

There are many ways to stabilize egg foams. The use of copper bowls creates a tight bond with reactive sulphur in egg white, preventing clumping and forming stable foam. It creates conalbumin-copper complexes further stabilizing the foam. Cream of Tartar – (potassium bitartrate) is an acidic salt, lemon juice or sugar can be added during foam preparation to create a smooth, stable foam that will not collapse and drain quickly. It is important to make sure that the egg whites do not have traces of any fats as they can be competitive with proteins and will interfere with foam formation (2,4).

Milk and Cream Foams

Milk foams are more fragile than egg foams and are often used as a topping for coffee drinks. They are stabilized by their proteins. Milk foams are more fragile and short-lived than egg foams due to their sparse proteins and resistance to unfolding and coagulation. Milk foams are created using a steam nozzle. Steam introduces bubbles into milk and heats them to coagulate whey proteins. It can be controlled to create microfoam or macrofoam. Microfoam has microscopic and uniform bubbles and is used in espresso-based coffee drinks which involve latte art as they give a definition and stability to the patterns. Macrofoam has large bubbles and is traditionally used for cappuccinos which requires a layer of foam to be on top of the liquid (2,4).

Ice cream is one the popular example of milk foam. A smooth base of milk, cream, sugar, and flavourings is cooled, aged for a few hours and then churned while freezing, which incorporates air to create a foam. Finally, the ice cream is hardened in the freezer for desired firmness, making it ready to enjoy. The term “overrun” refers to the amount of air in the ice. For example, if the volume of ice cream is doubled by adding air, the overrun is 100%. A higher overrun results in ice cream that is lighter and less creamy, while a lower overrun creates a denser and heavier texture. In contrast to this, the Indian kulfi is typically denser because it traditionally does not contain air. Kulfi is made by slow cooking and reducing milk to a thickened base, which is then frozen without churning. As a result, kulfi has a more compact and creamy texture compared to the lighter, aerated texture of ice cream. Some commercial kulfis, however, may incorporate a small amount of air for a smoother mouthfeel.

Whipped cream, a common type of cream foam, is aerated by whisking the cream until it becomes fluffy and can hold its shape. For best results, cream with a butterfat content of 30% to 36% is ideal, as the fat globules help create stable air bubbles. Unlike the protein foams of egg white, and milk, the cream foam is stabilized by fat. The whipping process forms a stable network that holds air bubbles in place. It’s best to use cold cream, as warmth can soften the fat and eventually the foam will collapse (6).

Foams are a key element in molecular gastronomy as well. They are made by incorporating natural flavours like fruit juices, vegetable purees, soups, and stocks with stabilizing agents such as lecithin, gelatin, or natural fats from cream and dairy products. Air is introduced by whipping the mixture with an immersion blender or using a cream whipper with N₂O cartridges. This technique used to create innovative textures and incorporate flavours without altering the dish was pioneered by Chef Ferran Adrià.

In conclusion, foams in food play a crucial role in enhancing the texture, appearance, and sensory experience of various foods. They create light, airy structures that can add volume. Foams contribute to the creaminess in mousses, and the frothiness in cappuccinos. They also serve as carriers for flavours, enhancing the overall eating experience. They can add visual appeal and elevate the presentation of culinary creations, making them an essential element in molecular gastronomy as well as food science.

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