# Use of Phase Change Materials for Food Applications--State of the Art in 2022
## 2 Food Applications of PCM
### Food Processing
#### 2.1.9 Solar Cooking  
Cooking is a type of food processing, specifically using heat to prepare food for consumption. Generally, cooking has two main purposes. First, cooking can prevent many illnesses possible if food is eaten raw. Cooking can kill or inactivate harmful organisms (bacteria, viruses,... ). Second, cooking can increase the digestibility of many foods which are inedible or poisonous when raw, like cereal grains, beans... For both purposes, the achieved effect depends on temperature, cooking time, and cooking method used. There is a large set of methods for cooking, like baking, roasting, frying, grilling, barbecuing, smoking, boiling, steaming and braising, which vary widely in the applied temperature (about 60 \({}^{\circ}\)C to 300 \({}^{\circ}\)C), the required time, and the method of heat transfer. In many developing countries, cooking in households is still mainly based on fossil fuels or biomass, which is a significant source of air pollution, CO\({}_{2}\) emissions, and recently also causing increasing cost. These problems can be avoided using solar energy for cooking, available in many developing countries. Thus, it is not surprising that research on solar cooking is plenty, and commercial cookers available. Basically, solar energy can be used as solar thermal as well as solar electric, both useful for cooking. However, solar electric, using PV modules to generate electricity which it is then used for cooking, is rarely discussed, an exception is [29]. Reasons are probably that solar thermal collectors are available for many decades, can be self-built, and have comparatively high conversion efficiencies. Nevertheless, electric systems have also distinct advantages; e.g., for indoor cooking when the energy from the sun has to be transported to the cooking site indoors, or for serving a wide temperature range. Solar thermal cookers are primarily classified based on their design regarding collecting solar energy as box-type, panel-type, and concentrating solar cookers. Moreover, they can be classified depending on how solar thermal energy is transported to the cooking vessel, thus by direct or by indirect heat transfer. Important is if cooking is outdoors at the solar thermal collector or indoors some distance away from it. Further on, as solar energy is not always available at the right time for cooking, or with sufficient power, integration of an energy storage is desired; typically, this is a thermal energy storage, even for solar electric cooking as discussed in [29]. The different issues regarding solar thermal cookers are discussed in many publications, e.g., [30; 31; 32]. Refs. [31; 32] also give extensive overviews of publications and results. Specifically with regard to thermal energy storage, TES, this can be done as sensible heat or latent heat, and can be integrated into the cooking pot, where the cooking pot is placed, or between cooking pot and solar thermal collector. For example, [31] describe a cooking pot with PCM integrated, which can be heated via the solar thermal collector in daytime, and can later be used for cooking separate from the solar collector. Ref. [32] describe a solar cooking system for baking, where PCM is integrated into the plate where the food is placed for baking; the PCM is a NaNO\({}_{3}\)--KaNO\({}_{3}\) mixture. Ref. [32] also  
Figure 5: Solar dryer with PCM, for drying agriculture produce (source: PLUSS Advanced Technologies Ltd.). describe a similar system that is not for baking but to cook with a cooking pot; the PCM is erythritol. Ref. [33] report on a solar thermal cooking system for 6000 meals per day, with a separate thermal energy storage; the system uses water/steam for heat transfer at 150 \({}^{\circ}\)C to 170 \({}^{\circ}\)C from the solar thermal collectors to the kitchen, and stores heat in a pressurized hot water tank. Ref. [34] give a review of parabolic solar cookers with thermal energy storage, specifically parabolic solar cookers as they achieve high temperatures in short times, so allow most types of cooking.