What is Frying?

What is Frying?

Frying is an old and widely used method of cooking and processing food. Typically, a food is immersed in heated oil for a short duration in a process known as immersion-oil frying. Numerous types of edible oils of plant and animal origin are used in frying, depending on regional availability. Palm oil is often used in Southeast Asia, coconut and groundnut oil in the Indian subcontinent, and olive oil in the Mediterranean region. During the last five decades, the Western food industry has become increasingly dependent on the frying process to manufacture a variety of snack foods. Fried foods such as potato chips, French fries, and fried fish and chicken have gained worldwide.

Physicochemical Changes in Foods during Frying

The immense popularity of fried foods is due to the unique flavor and texture imparted to food as it is fried. Many fried foods typically have a porous, crispy outer crust layer with unique flavor but are also soft and moist internally. With starchy foods, it is generally agreed that the crust layer developsas starches in the food gelatinize and the outer layer rapidly dries. However, the kinetics andmechanisms involved in crust formation and related structural changes have yet to be wellunderstood. These mechanisms are dependent on the physical and chemical properties of the foodmaterial and the oil used in frying. The complexity of the frying process can be seen in many aspects.

For instance, the structure and thickness of the porous crust layer is dependent on the product composition, the processing time, temperature, and composition of the frying oil and material beingfried. Heat transfer between the oil and food surface is largely due to the convection mode, whereasheat flux across the crust layer is characterized by the conduction mode of heat transfer.

Inter- and intra-sample irregularities pose a significant problem when trying to understand the basic driving forces involved in the movement of oil in a food during frying. This heterogeneity has led to the development of product-specific, empirical models that yield little in the way of fundamental knowledge. As a result, only limited progress has been made in developing a mechanistic understanding of the frying process. Frying is often the preferred method of cooking for several reasons. The relatively high temperature of the oil used as a heating medium in the process sharply reduces the cooking time, resulting in desirable sensory characteristics like crispy texture and pleasant aroma (see Sensory Evaluation, Texture in Solid and Semi-solid Foods).

In fried foods, such as potato hips and noodles, a product is fried until most of the moisture is removed and a porous structure is created throughout the product. With French fried potatoes, among other foods, the potato strips are fried for a sufficient duration until the outer region becomes porous and stiff, giving it a crispy texture, while the inner region is cooked and moisture is retained. Chemical changes create desirable aromas. The amount of oil absorbed during frying increases the total fat content and caloric value of a food, of concern when a low fat diet is desired.