THE ACADEMY OF BUSINESS STRATEGY
FROZEN TECHNOLOGY BLOG
Frozen Food- Quick Frozen Food. Do you know the difference?
Roberto Nardi (CBS) MA
The low temperature is the best conservation method for foods, from the nutritional and hygienic point of view, as it blocks the deterioration without altering its nutritional properties. Frozen vegetables and frozen fish, if well preserved, have the same nutritional value as fresh. For those who have not available freshly caught fish and fresh vegetable, the frozen products represent the only real guarantee of freshness.
But there are differences of quality connected with the technology used to cool a product, and often there is no clarity about a Frozen product and a Deep Frozen or a Quick Frozen Product. The way of heat transferring strongly influences the physical characteristic of a product below 0°C, and the speed of cooling a product (it is not relevant if we are talking of a fish, a vegetable, a meat or a meal) delivers different organoleptic tastes and quality that are perceivable during an accurate degustation.
To better explain these differences it is necessary to understand what happens during the cooling of a product. For a certain period around 0°C the temperature remains constant (it is the moment in which the latent heat changes the status of the matter, meaning that the water inside the food is transforming in ice), than the temperature goes down according to the temperature of the cooling fluid used to cool the product. This is the moment during which the water contained into the product is transformed in ice crystals.
The lower is the temperature of the fluid, the higher is the speed of cooling. As a consequence, the shorter is the cooling time, the smaller are the crystals of ice that are formed during the freezing time.
The smaller are the ice crystals dimensions the better is the quality of the final product. Because when the ice crystals dimensions are smaller than the cells dimension of the product, the ice crystals don’t break the walls of the cells. On the contrary, when the ice crystals dimensions are bigger than the cells dimension, some of the internal liquid of the cells can come out during the defrosting time (this phenomena is easily visible when you defrost frozen raw meat).
Quality of the final product is better when the cells remain integer after the defrosting. Of course the integrity of the cells are related to the ice crystal dimensions connected to the process used during freezing.
Technically, Frozen Food (FF) is a product that it is thermally treated to reach a temperature below 0°C. The process aiming to reach this temperature is called freezing. Without any specific definition of the period of time used to reach the frozen temperature. It is defined Quick Frozen Food (QFF) a special fast cooling process, said deep freezing, able to reach very quickly the low temperature, below -18°C, and able to preserve it in a very accurate manner.
To cool a product, Industries normally blow air in direct contact with the product at a temperature around -40°C. This very low air temperature is reached in big heat exchangers where a fluid (usually Ammonia or Freon) is expanded after having been previously compressed.
Alternatively, “cryogenic” fluids are used (nitrogen or carbon dioxide) at very low temperature (-70°C or lower). Direct injection of liquid carbon dioxide or liquid nitrogen over the products allows cooling down very rapidly.
Both the systems are widely used. Air-cooling is cheaper in cost but requires bigger initial assets investments. Final product quality is very good in both the cases, because the ice crystals are very small with such low temperatures. We can conclude that during these treatments the crystal ice dimensions are smaller than the cells dimensions. And both these technologies deliver products that are Quick Frozen Food. A Quick Frozen Product must be kept at a temperature below -18°C during the period of storage and sale (legal definition in some Countries) to guarantee the dimensions of the ice crystals.
But to freeze products it is not necessary only to use air temperature at -40°C or cryogenic fluids. It is possible to use also higher air temperature. For example, the temperature of a domestic freezer (usually at -12°C) or of a cold chamber (at -18°C.) The product will be frozen in a longer period, depending from the size and mainly form the thickness of the product. The ice crystals dimensions will be usually bigger than the cells dimension: the product will be protected by the risk of fermentation (microbiologically safe), but not enough from the physical damage of the cells. It is important to underline that these frozen products have a shorter shelf life if compared to the QFF products (they can be kept in cold store for some months instead of for one or two years).
The ice crystals dimensions are not stable during the period in which the product is stored; they change gradually according to the variations of temperature in the cold store. As a consequence, if a QFF is not well maintained, and the temperature rises, the ice crystal dimensions grow and the product become a FF.
With big equipment to obtain cold at low temperature, Industry can produce QFF. If well preserved during transport and storing, quality of these products can be guaranteed for a long period of time.
Frozen food domestically produced cannot have micro ice crystals dimensions and these products can be well maintained only for few months at home.
A Frozen product cannot be transformed in a QFF (when macro ice crystals are formed, they cannot become smaller if you decrease the temperature). Shelf life of frozen products is a relevant aspect of study. So important that it is worthwhile to threat this subject in another article.
ABOUT THE AUTHOR
Roberto Nardi (CBS) MA is an approved Certified Business Specialist (CBS) with the Academy of Business Strategy and his specialist subject is frozen technology. He has achieved a Masters in Chemical Engineering from La Sapienza University of Rome. He has been employed as a Vice President, Director, Chief Engineer, Marketing Manager and Consultant for various companies and has experience within the food technology, industrial equipment and food product design industries His clients or employers have included Unilever. He has geographical working experience in the UK, USA, Netherlands and Italy. He speaks Italian and English. His service skills incorporate global product development strategy, business process improvement, innovation process management and frozen technology.