Understanding the Cooking of Food in a Domestic Microwave Oven

Since its creation in 1945, the microwave has become a popular method of cooking food on both domestic and commercial scales. Despite its popularity, manufacturers have increasingly struggled to provide food products with desirable textural attributes similar to those achieved via conventional oven cooking. A prime example of this is in the potato industry where it is difficult to maintain crispy/crunchy textures of microwaved products due to moisture migration from the centre of the potato to the surface. Microwave heating primarily relies on dielectric heating with heating occurring via dipolar polarisation and ionic conduction. Previous research in this area has identified water as the main driving factor of dielectric activity due to its polar nature. In terms of this thesis, research has been conducted with the aim of understanding the science required to produce a potato chip product within the microwave oven which is able to maintain a moisture rich soft centre with a low moisture crispy exterior.
The research has concluded that creation of crisp products within a microwave environment is multifactorial and strongly depends on storage time, selection of potato part and coating constituents, as well as where in the production process a coating is applied (pre fryer, post fryer or post freezer). Further investigation has also shown the importance of water and highlighted that water content alone is not an indicator of dielectric activity, but rather the ratio of free:bound water within the food product and how moisture moves throughout the product as a function of time. It has been found that addition of a polar and ion rich coating can improve product crispness of the base product although not to the same degree as deep fat frying and conventional heating. However, it must be noted that during the first 8 weeks of storage the product constantly alters in terms of moisture content, dielectric activity, acoustic activity, mechanical force measurement, recon loss and ratio of bound:free water with particular reference made to the role of moisture and sodium chloride as a ‘chemical oscillator’. This indicates that the manufacturer should not sell their product until at least 8 weeks after production if they require a high efficacy for their product. Whilst the end product produced was not as crisp as required, the research is promising with further work being required in terms of coating formulation to improve the end product crispness of potato based products within the microwave. Further work is required within the area of moisture migration due to the complex nature of the product involved.