GRADING - Improving food flavor by using a microwave smart and targeted heating

The Grading project represents a collaboration between Electrolux Italia Spa and the Department of Industrial Engineering. Among all the household appliances produced by the company, this thesis focuses on ovens, particularly microwave ovens. Currently, commercial microwave ovens use magnetrons as microwave generators due to their low cost and satisfactory efficiency (around 70). However, a major drawback is the inability to control their operation, resulting in a nearly constant stationary electromagnetic field inside the oven cavity with fixed positions of high and low energy areas. Stirrers or rotating plates are usually employed to mitigate this issue, but uneven heating remains the primary problem. As a solution, a new type of microwave generator is gaining increasing interest: solid-state generators. These generators offer precise control over operating frequency and phase shifts between channels, as well as power levels at each channel. Adjusting these parameters alters the electromagnetic field distribution in the cavity and the positions of hot and cold areas. Therefore, solid-state generators have the potential to minimize the issue of non-uniform heating. Considering that the adoption of new technologies or modifications to existing devices in companies mainly depends on economic convenience, improved efficiency, and added value for the consumer, this project focuses on the third aspect. Economic and efficiency improvements are outside the control of companies like Electrolux; therefore, this thesis aims to explore the effect of using a solid-state system instead of a magnetron-based one in Electrolux devices, specifically in terms of cooking performance and the quality achieved after cooking. Additionally, special attention is given to testing various approaches, such as the use of finite element simulations, to determine their advantages and limitations in testing and setting cooking cycles for this new category of microwave ovens that employs solid-state generators. A multidisciplinary and scientific approach forms the basis of the methodology. Each research initiative begins with an understanding of the phenomena that occur during the cooking of the food or product under analysis, the role of ingredients, and how changes induced by different cooking processes influence the quality parameters evaluated by consumers. Simulations are conducted using Comsol Multiphysics, where the model of the oven is created. Data collected from instrumental and sensory analyses after experimental tests are always subjected to statistical analysis. The virtual model of the oven proves to be a valuable tool for managing the complexity associated with solid-state technology. This model allows the development of cooking cycles (sequences of configurations of setting parameters) that ensure both high efficiency and uniformity of heating. However, for a complete definition of cooking cycles for specific products, including the level of power and cooking time, experimental tests are also essential. The experimental part of the research demonstrates the superiority of solid-state technology over magnetron-based systems in terms of heating uniformity, which directly translates to higher food quality. Despite these advantages, microwaves alone cannot achieve the level of quality desired by consumers due to their nature. The key to reducing cooking time while maintaining high quality standards stands in combining microwave technology with other cooking methods. This thesis proposes and tests a procedure to facilitate the creation of combination heating strategies, showing its effectiveness in enhancing cooking outcomes. The results obtained regarding the advantages in cooking performance that solid-state systems can provide over traditional magnetron-based ones constitute a significant factor in guiding the decision to adopt this technology for domestic microwave ovens, particularly when its cost will ensure economical convenience.