# Use of Phase Change Materials for Food Applications--State of the Art in 2022
### Food Applications--Overview  
\"Food\" can be defined differently. The United Nations Environment Program, UNEP, defines \"food\" as \"Any substance--whether processed, semi-processed or raw--that is intended for human consumption. Food includes drink... \", \"It does not include cosmetics... \" [4]. This definition is used here. Availability of food is essential, and if insufficient it is a main cause of poverty, even political instability. Food loss [4], e.g., by spoilage, and the cost of energy related to food, are a growing concern. Thus, this paper reviews the state-of-the-art of the use of PCM in food applications, and its potentials. Early humans hunted and gathered food in the natural environment, and consumed it as is, immediately. With the use of fire, food could be cooked, thus modified in a way that it often can be digested better, also that harmful bacteria are killed. For later use, e.g., during winter, with food surplus even for trade, storage and transport required food preservation. This was done by drying food using the sun, wind, the fireplace, by salting food etc. Nowadays, practically all food is produced, in a non-natural environment, typically on a scale larger than for personal consumption, and most food is modified also in some way. Further on, applications like cooking serve for preservation as well as  
Figure 1: Ideal phase change: heating and cooling T(t), as well as h(T) and c\({}_{\text{p}}\)(T). modifying food for consumption. The purpose, and so what is done, as well as by whom it is done, has a big effect how something is done, and so the technical solution for an application. Consequently, an overview to structure the applications, specifically regarding food processing, preservation, and cold chain, is needed. It is shown in Figure 2.  
Nowadays, only few people consume food that is self-produced, meaning grown, gathered, or hunted. Consequently, nowadays food is practically never consumed directly, e.g., directly after food harvest. Even food that is consumed unmodified usually requires transport, and also storage, on the way from its production to its final consumption. Consequently, food needs to be preserved, to remain fresh, to keep its nutritional value, and to avoid spoilage (meaning it becomes unconsumable e.g., for health reasons). The straightforward way of food preservation, thus without modifying the food, is by keeping food cold, (in case of warm meals, which are modified food, directly before consumption by keeping them hot). Most food however is not consumed unmodified. Food modification, meaning the transformation of natural products into food, or of one form of food into other forms, is commonly called food processing. Food processing is nowadays done by the food industry, in addition to the households and restaurants. Due to its importance, it is not surprising that many food processing methods are for food preservation. Food processing includes food preservation by thermal treatment like refrigeration and even freezing, by boiling, sterilization, pasteurization, and also by drying in case it is done by temperature and heat. Besides, non-thermal methods of food preservation are drying methods like salting, vacuum packing to keep humidity and even air out, addition of preservatives, irradiation, or also high hydrostatic pressure. Food processing, defined as transformation of natural products to food, or of one form of food to others, however does not just include food preservation; thus, this field of applications is separated in Figure 2. Food processing also includes a wide range of processes which are not for preservation, e.g., processes for making natural products edible, turning ingredients into familiar food, or for modifying food with respect to its content of calories etc. thus dietary needs. Some of these processes are thermal, like baking bread, frying sausages, cooking meals or pre-cooking them for ready-to-eat or heat-and-serve foods.