Puffed foods are mainly made from grains, potatoes, or beans, processed through pressure, heating, or extrusion to alter their structure and volume, resulting in a porous and fluffy texture. But what magic does puffing possess that transforms ordinary ingredients like corn, wheat, potatoes, and rice into various shapes-round, triangular, spiral, star-shaped-and gives them a crispy, crunchy texture? A professor from the Department of Food Science at Fu Jen Catholic University points out that to understand puffing, we can start by explaining the principle of popcorn. Popcorn is made from hard, dry corn kernels, functioning like a pressure cooker. Once heated, the internal moisture of the kernel increases pressure, and the weaker parts of the outer shell become pressure outlets. The hot water at these outlets, due to the reduced pressure, instantly turns into steam and expands, forcing open the corn kernel shell and extruding the soft, gelatinous paste made from the gelatinized starch granules within the kernel.
Because the water vapor inside a corn kernel expands instantaneously from multiple points, like tiny bombs exploding simultaneously, it creates numerous small bubbles within the kernel, increasing its overall volume. After popping, these bubbles merge, cool, and solidify, while the water vapor evaporates, reducing the moisture content. The originally soft, gelatinous batter transforms into beautiful, white popcorn. Therefore, heating, and sometimes pressurizing, ingredients containing starch and water causes the water vapor to expand the food's structure (the popping of popcorn), a series of reactions, is called puffing. Street popcorn is made using the same principle, the difference being that it lacks a hard outer shell; the pressure comes from a pressure cooker. The unique popping sound of popcorn is caused by the sudden release of pressure when the pressure cooker is opened, causing the water inside the kernels to instantly turn into gas, and the high-pressure gas inside cannot escape in time, producing the sound.
In food factories, extruders are primarily used to produce various puffed foods. Unlike pressure cookers for popcorn, extruders can accept granular or powdered raw materials and combine functions such as mixing, kneading, and steaming. They can also create three-dimensional shapes like animals and letters using different molds. Because the process also involves heating and sterilization, as well as reducing moisture content, puffed foods can have a longer shelf life without preservatives. Puffed foods can be further divided into two types based on their production methods:
1. Direct extrusion puffing, common products include "Guai Guai" (a type of puffed snack) and corn sticks. After the raw materials are mixed by the machine's rotating shaft, they are rapidly sheared and heated by steam to provide the high temperature and pressure required for puffing in a short time. The material is then extruded through specific shaped molds and cut into the desired shape by a cutter. The extrusion process results in a fluffy effect due to the ambient temperature and pressure. Further baking is then performed.
2. Indirect extrusion puffing, common products include "Bao Ka Ka," "Kola Guo," "Man Tian Xing," and rice crackers (Senbei). The extruder provides the mixing, steaming, and shaping functions, while puffing is achieved through baking, frying, or microwave heating. This method allows puffed foods to have diverse textures and flavors, creating a unique eating experience.
While puffing is crucial, the later stages of the manufacturing process are equally important in creating irresistible snacks. For example, spraying oil on the surface of the product before baking eliminates the need for frying, achieving a crispy texture. Therefore, a product labeled "non-fried" only indicates that it hasn't undergone frying, not necessarily that it's low in oil. Many people are wary of oil, but from a manufacturing perspective, oil actually plays many important roles in improving product quality. For instance, in popcorn making, the right amount of oil acts as a heat transfer medium, ensuring even heating of the dried corn and reducing localized burning; adding oil during the mixing and extrusion of ingredients prevents the product from becoming too hard; in the indirect extrusion puffing process, frying causes the product to puff up, creating a thick, crispy texture; spraying oil during the seasoning stage allows seasoning powder to adhere evenly to the surface; and using oils like butter and coconut oil can add unique aromas to the product.
Puffed foods often contain large amounts of salt and sugar, which primarily serve two functions: adjusting flavor and regulating the degree of puffing and porosity of the finished product. Since puffing relies on the gelatinization reaction between water and starch granules, adding small amounts of water-soluble sugar and salt to the ingredients can affect the density of puffed snacks. Besides oil, sugar, and salt, you've likely seen various food additives listed on puffed snack packaging. Why are food additives needed? The most common food additives are antioxidants, such as tocopherol (commonly known as vitamin E), which prevents fat oxidation. Additionally, adding small amounts of quality improvers can prevent clumping during mixing and cooking, adjust food acidity, and ensure even mixing of fats and water; examples include silica, glucono-delta-lactone, phosphates, and calcium carbonate. However, there are many types of food additives with these functions, and how to combine them effectively is a secret formula for manufacturers.
