## 3 Roasting Process
### Microwave Roasting  
Another alternative method to traditional roasting is microwave energy. This method is currently used for various food heating processes, because microwaves can penetrate food, accelerating the heating process and resulting in improved roasting quality and taste [45].  
The fundamental physical principle governing these technologies is a simple relationship between microwave wavelength and frequency (oscillations of the electric field per second). Another crucial factor is the capacity of materials to absorb microwave energy, a property known as dielectric heating. The ability of molecules to align with an electric field is influenced by their dipole moment and mobility. Molecules possessing a permanent dipole moment can orient themselves, either fully or partially, with an external electric field through rotational motion. In gaseous or liquid phases, molecules can rotate in synchrony with field frequencies of up to 10\({}^{6}\) Hz. However, they cannot indefinitely follow rapid field reversals, resulting in phase shifts and dielectric losses. This phenomenon depends on both the dielectric coefficient (permittivity) and the size (mass) of the molecules. As field energy is transferred to the medium, electrical energy is converted into kinetic or thermal energy. A common model for this process is molecular friction. Numerous polar substances exhibit dielectric losses within the microwave frequency range [46].  
Upon penetration of food by microwaves, the electromagnetic field triggers water molecules and other molecules to vibrate, oscillate, and rub against each other, generating heat. This process generates water vapor, which is forced out of the food, leading to a high degree of selective drying [9].  
[PERSON] et al. (2014) applied an innovative microwave oven to roast almonds. Their oven was equipped with a stirring paddle, enabling continuous mixing of the almonds during the roasting process. The oven had a nominal power of 1300 W. The roasting conditions applied in this study were as follows: light roasting: 50% power for 105 s, followed by 60% power for 45 s, mimicking light roasting in a hot air oven system; medium roasting: 70% power for 148 s; and dark roasting: 60% power for 54 s, followed by 70% power for 126 s. These methods corresponded to power outputs of 231 W, 608 W, and 773 W, respectively. After microwave roasting, the authors conducted various sensory analyses. The results indicated that microwave roasting produced almonds with a similar flavor and crunchiness to those roasted in a hot air oven. To achieve comparable results, the following power inputs were required: light roasting: 0.8 W/g for 150 s; medium roasting: 0.9 W/g for 148 s; and for dark roasting: 0.91 W/g for 180 s [35].  
[PERSON] et al. (2014) studied the differences in roasting results for peanuts using various conditions. Traditional oven roasting was conducted at temperatures of 135, 163, 177, and 204 \({}^{\circ}\)C for 5 to 20 min, while microwave roasting was performed for 1 to 3 min. After roasting, the researchers evaluated for color, flavor, and moisture content. They reported no significant differences in color and flavor between peanuts roasted using microwave or traditional oven methods [47].  
However, it was observed that microwave energy was inadequate to trigger the Maillard reaction, which is necessary for the formation of desirable volatile flavor compounds such as aldehydes [36].