# Use of Phase Change Materials for Food Applications--State of the Art in 2022
## 2 Food Applications of PCM
### Food Storage and Transport  
#### 2.2.1 Background  
Nowadays, food is practically never consumed directly, e.g., directly after its harvest. Even food that is consumed unmodified is usually transported and also stored on its way from production to consumption. Storage and transport on the way from production of raw food to consumption takes place many times, between industry, distribution centers, supermarkets, households and restaurants, and the consumer.  
During the time of storage and transport, food needs to be preserved, to remain fresh, to keep its nutritional value, and to avoid spoilage. The straightforward way of food preservation, thus without modifying the food, is thermal: by keeping food cold, or for warm meals directly before consumption by keeping them hot. As already discussed before, in the background on food processing (Section 2.2.1), for food preservation it is recommended to keep food not within a range between about 10 \({}^{\circ}\)C and 60 \({}^{\circ}\)C. Keeping food at lower temperatures distinguishes between keeping food cold and keeping food frozen. Keeping food cold, called refrigeration, is typically done at 4 to 8 \({}^{\circ}\)C (useful for shorter periods), and keeping food frozen, below 0 \({}^{\circ}\)C it is called freezing, is typical done at \(-\)18 \({}^{\circ}\)C (useful for longer periods). Keeping food above 60 \({}^{\circ}\)C is just for distributing and keeping ready meals for consumption.  
Keeping food in a narrow temperature range for preservation is typically done in a well-insulated space. Thus, food preservation during storage or transport typically needs less heating or cooling power than making food hot or cold in food processing, including bringing it to the temperature for preservation. Technical solutions for storage and transport, compared to processing, focus thus more on keeping the temperature in the desired temperature range, which makes PCM very suitable for these applications.  
Storage solutions keep food in the required temperature range while being stored at a given location. For this, the storage space is well insulated to reduce heat exchange with the ambient, and remaining heat exchange is compensated by a heating or cooling device, a pre-charged PCM, or by a combination. Because food storage and transport happen on many different levels, it is not surprising that there is a wide range of technical solutions. An approach for cold storage of food is to combine cold production with cold storage, typically an electrical driven compression cooler with an ice storage, and to supply cold if needed to the space where food is stored. Another approach is to place the cold storage into the space where food is stored, and which is well insulated, while having the cold production unit outside. Then the cold production unit can even be detached during transport, or storage at different locations. Independent transport containers usually use pre-charged PCM instead of a heating or cooling device, because in transport a power connection is usually missing. However, they can also be used for storage.  
The focus now is on storage solutions with a fixed location where a source of electricity is available or can be made available. The advantage of using PCM to shift or buffer heating or cooling loads is typically an increase in energy efficiency, reduction of cost, and having backup in case of power failure.