Marshmallow is a soft, chewy confectionery that has been enjoyed for centuries. It is known for its fluffy texture and sweetness. Marshmallow is essentially a foam stabilized by gelatin. They are part of the aerated confections category, and they could be either grained and ungrained, depending mainly on the sucrose/corn syrup ratio. 

The main characteristics of this candy is its low density, which can go from 0.25 to 0.7,  achieved by aeration during the whipping stage. 

As air is incorporated into the gelatin-sugar mixture, it creates a network of tiny bubbles throughout the marshmallow, relying on the expansion of trapped air to achieve the desired density. This results in a molecular structure primarily consisting of a matrix formed by the interconnection of long chains of gelatin molecules. The sugar and corn syrup serve as the amorphous matrix that holds the gelatin in place, while gelatin acts as the stabilizer, securing the air bubbles within the confection. Other stabilizers are used instead or in combination with gelatin.

Texture of the marshmallow will be influenced by various factors such as: amount of air incorporated, ratio of sucrose/corn syrup (grained/ungrained), type of stabilizer used and amount, and the final water content. 

Marshmallows are typically extruded and covered with starch or powdered sugar or deposited in starch molds to be dried to lower solid content and get distinctive shapes that could be enrobed afterward.

The process of making marshmallows involves several key steps and the base of the marshmallow main properties are in the aeration step:

Mixing, Cooking, and Heating Systems: Sugar, corn syrup, fat, and water are cooked in large kettles until the desired temperature is reached. If starch is used, it is added during this step. This process is employed in both batch systems (using steam jacket kettles with mixers) and continuous systems. Achieving the correct temperature is crucial to ensure the desired moisture content. For deposited marshmallows, some moisture can be lost later. Typical cooking temperatures fall within the range of 107-110°C (225-230°F).

Stabilizer Hydration: Proper hydration of stabilizers is essential. Gelatins and albumens should be mixed with water at a ratio of 2:1 to 4:1 for an adequate duration to eliminate lumps.

Stabilizer Addition: Hydrated gelatin (or other stabilizers) can be incorporated either before or after the cooking process. While the preferred method is to add gelatin after the cooked syrup has cooled, in batch cooking scenarios, it is not uncommon to introduce hydrated gelatin directly into the batch towards the end of the cooking phase, along with other heat-sensitive ingredients like flavors. In continuous production systems, the hydrated gelatin is typically introduced into the cooked slurry through a flow in the static mixer.

Minor Ingredients Addition: Flavor and color are added after cooking or through continuous injection systems into the candy stream.

Aeration: This step should occur at warm temperatures when the candy is still liquid, just above the stabilizer gelatinization point, allowing air bubbles to rapidly stabilize as it cools down. Various methods, such as whipping the fluid candy mixture to expose it to air or injecting air directly into a confined container with the liquid mixture, can be used for aeration. For improved bubble distribution and controlled final density, a continuous pressure beater can be employed. Here, a flow of candy meets a flow of air under pressure, and a mixing head with a rotor breaks large bubbles into smaller ones. It's important to note that the characteristics of the resulting air cells can vary significantly depending on the chosen aeration method. The average bubble size in a typical marshmallow is between 20-25µm.

Shaping and Forming Equipment: Marshmallows are typically deposited into starch molds or onto a moving conveyor, or they can be extruded. Marshmallow deposited into starch remains in the mold for several hours until it reaches the final humidity. It's then cooled down to set the gelatin. Once it reaches 8-10% moisture content, it is shaken out and sent for packaging or undusted and sent to enrobing machines for chocolate coating. Marshmallow deposited on moving bands and extruded should have its final solids formulated and utilize quick-set stabilizers. To prevent sticking to equipment or to each other after cutting, the marshmallow is coated in starch or confectioner's sugar.

Packaging: Marshmallows are typically packaged in plastic bags or boxes. Often, they are dusted with a mixture of powdered sugar and cornstarch to prevent sticking. Some variations of marshmallows may be available in resealable bags or display containers for added convenience. If it's a chocolate-covered marshmallow, it is usually sent for individual wrapping in a flow pack.

The balance between sucrose and corn syrup plays a crucial role in defining the primary texture characteristics of this candy and can significantly impact its shelf life if not formulated correctly.

For ungrained marshmallow sugar: corn syrup ratio, must contain more than 50% corn syrup solids to prevent sugar crystallization. In contrast, grained marshmallow contains higher levels of sucrose to create a supersaturated solution that promotes graining. Additionally, graining can be induced with powdered sugar or fondant before forming.

The percentage of gelatin or stabilizer required depends on whether the marshmallow is being extruded or deposited.

Due to high aeration rates, colors can fade into pastel-like tones, which must be taken into consideration during the formulation process.