# Use of Phase Change Materials for Food Applications--State of the Art in 2022
## 2 Food Applications of PCM  
### Food Processing  
#### 2.1.1 Background  
Food modification, meaning the transformation of natural products into food, or of one form of food into other forms, is commonly called food processing. In addition to households and restaurants, food processing is nowadays done on a large scale by the food industry. Food processing includes non-thermal processing like grinding grain to make raw flour, as well as thermal processing like cooking. Thermal food processing methods comprise those for preservation of food and not for preservation. Those food processing methods for food preservation can again be split up into making food hot/cold, specifically refrigerating and freezing, where the food is then kept at the temperature during the following storage and transport, and only temporary heat/cold treatment, like boiling, sterilization, pasteurization, and drying, if done by temperature and heat. Those food processing methods which are not for food preservation focus on modifying food for making natural products edible, for turning ingredients into familiar food,... like baking bread, frying sausages, cooking meals or pre-cooking them. Thermal food processing methods play a crucial role in making natural products edible, in food preservation, and thereby reducing food loss. Heating has two main purposes. Heating can prevent many foodborne illnesses, as heating can kill or inactivate harmful organisms (bacteria, viruses,... ), and heating can increase the digestibility of many foods which are inedible or poisonous when raw, like cereal grains, beans... Heating methods comprise methods to prepare food for consumption, like baking, roasting, frying, grilling, barbecuing, smoking, boiling, steaming and braising, as well as methods for food preservation, like boiling, sterilization, pasteurization, and also drying in case it is done by temperature and heat. Cooling, in contrast, is mostly used for food preservation, for food to remain fresh, to keep its nutritional value, and to avoid spoilage (meaning it becomes unconsumable e.g., for health reasons). Besides for food preservation, cooling is also used to prepare foods like ice cream. The type of food and the purpose of thermal processing determine the temperature and time of a process. Like any living organism, bacteria need temperatures not too cold and not too hot to grow etc., and well outside this temperature range they die. Therefore, for food preservation, it is recommended to keep food not within a temperature range between about 10 \({}^{\circ}\)C and 60 \({}^{\circ}\)C to avoid rapid growth of bacteria. Keeping food at lower temperatures limits their growth. Just keeping food cold is called refrigeration, and typically done at temperatures of 4 \({}^{\circ}\)C to 8 \({}^{\circ}\)C and useful for shorter periods. Keeping food below 0 \({}^{\circ}\)C it is called freezing, typical is at \(-\)18 \({}^{\circ}\)C, and useful for longer periods. Keeping food at higher temperature can significantly reduce the presence of bacteria, even kill all bacteria if the temperature is high enough and if given sufficient time. According to [5], \"Since none of the bacteria related to foodborne illness can survive, let alone reproduce, at moderate temperatures, holding food above 140 \({}^{\circ}\)F/60 \({}^{\circ}\)C indefinitely is safe. This is why the soup at your local lunch counter can be kept hot all day long in a heat-controlled container and why hot buffets use steam baths to keep the foods warm.\" Processes at higher temperature but for limited time can reduce the presence of bacteria to \"safe\" levels for near-term consumption or for an extended shelf life. Cooking food even kills most bacteria, however a minor (yet safe) number can survive, and if given the right temperature and time they can reproduce again to unsafe quantities. Thus, after cooking fast cooling is advisable if later food storage is intended. Not for food preservation are methods that via chemical and physical reactions improve flavor and increase nutritional value.