To begin our new series, "What you need to know about refrigeration", we will be taking a look at one of refrigeration's most important applications, namely the cold storage room. As well as explaining the specific features of cold storage we will also explain on the "how" and the "why". This series is based on a number of complimentary e Learning modules from Danfoss for individual self-tuition on a PC. They are suitable for any type of student, from beginners to refrigeration experts.
Humidity and Air-flow Rate
Humidity also affects food quality. Microorganism growth is also influenced by the moisture content of the ambient air. The moisture content of food products promotes the growth of microorganisms. In a low-humidity atmosphere, moisture will be removed from the product causing it to lose both weight and quality. We therefore need to maintain a certain level of humidity in the ambient air in order to keep food products fresh and prolong their shelf life. In order to continuously provide the proper moisture content we need to maintain a constant temperature. In addition to the moisture content, the air-flow rate is also important for the quality of food products. The air exchange rate (the rate at which the existing air is replaced by fresh) is what ensures good air quality in the cold store, but the flow rate also affects the cooling and dehydration of the product: a higher rate increases the transfer of heat from the product but also its dehydration rate. An increased rate of dehydration means that more water will be removed from the product, leaving a lower moisture content. We therefore have to provide for an appropriate air-flow rate within the refrigeration plant. The product factor (PF) depends on the air-flow rate and the type of food product. In general, higher air-flow rates increase the product factor, but this then also increases the dehydration rate. Some products have a surface that favors dehydration (lettuce, mushrooms) while other products, such as apples are less favorable.
Product | Humidity |
Potatoes | 90-95 |
Tomatoes | 90-95 |
Apples | 90-95 |
Garlic | 65-70 |
Chicken | 95-100 |
Fresh fish | 95-100 |
Conclusion
This concludes the first part of our consideration of cold storage rooms, in which we dealt with produce being refrigerated. Construction of a suitable cold storage room, will be dealt with in the next episode in this series. This will concentrate on the practical challenges and requirements for setting up such an environment.