Facebook Twitter ShareAddThis
The Science of Cold and Freezing Food

The Science of Cold and Freezing Food

What's the difference between cool and freezing when it comes to food preservation? A closer look at freezing food preservation, explained by science.

By on

Whenever winter comes to mind, it is immediately associated with the cold. Back in antiquity, it was already widely known that food lasted longer in the cold winter months. Incredibly, as long ago as 2000 B.C. in Mesopotamia, deep pits used to be excavated and filled with snow to preserve food. It did not take long to transfer this experience to the first ice-houses, extremely cold places which paved the way to modern refrigerators. However, the loose term of “cold” when applied to food is a simplification true connoisseurs cannot afford to make, because it lends itself to too many interpretations.

First and foremost, the term “cool” refers to the temperature inside a refrigerator, which ranges from 0 to 15° C. Its function is to preserve food in perfect condition for a few days after buying it. Then, there is freezing, which takes place at temperatures below -15 °C. Freezing entails a slow transformation of the moisture contained in food into large elongated ice crystals, which cause the tissue and cell walls to break down.

Deep freezing, on the other hand, takes place at temperatures lower than -18 °C: in this case, a large number of small ice crystals are formed which cause no significant damage to the structural elements of the food. If you read our science articles regularly, you will already understand when it is useful to freeze rather than deep freeze food, and vice versa. Large ice crystals pierce the tissue and we can exploit this phenomenon to tenderize rather tough meat: freeze it for a few days and then leave it to thaw out; you will notice how much more tender it is! Conversely, if you are dealing with a perishable food you wish to preserve, whose structure is weak, you are advised to deep freeze it.

Generally speaking, this is true of ready prepared food (in the sense that you have already cooked them yourself, heaven forbid that you buy ready-made packaged food!), particularly first courses and pastries. So, in brief: raw ingredients, especially if they need to be tenderized, ought to be frozen; cooked dishes should be deep frozen. However, both freezing and deep freezing techniques present one small problem: they are slow. To reach such low temperatures, it takes several hours, a dozen or so according to the electrical appliance being used. Hence the invention of the blast chiller.

Identical in appearance to a freezer or deep freezer, it is able to take a food from 0°C to -40 °C in just 3-4 hours. In the same amount of time, it is also able to reduce a temperature from +9 °C to -18 °C, while it takes no more than a couple of hours to go from +90 °C to +3 °C. In the latter case, the correct term to use is “positive blast chilling”. This type of equipment owes its incredible performance to a special cooling system based on powerful fans. But what are the advantages of a blast chiller which, optimistically speaking, will cost around 1200 Euro (well spent, believe me)? Its prime boast is that it can freeze or deep-freeze while immediately destroying any pathogens. This is why it is advisable to “blast chill” fish destined to be eaten as sushi. And, on the subject of sushi, the speed at which a blast chiller works obviously reduces preparation times by (at least) fifty per cent.

Chilling a dessert can be done in about one hour, while a gelatine will firm up in a few minutes. As an added bonus, there are two more advantages smarter chefs will surely appreciate. On one hand, such a rapid chilling process allows the product to lose less weight, which translates into a cost saving. On the other hand, the speed at which the process takes place puts an immediate stop to any resulting enzymatic deterioration, and therefore preserves intact all the organoleptic properties of the food. I am convinced that, whenever you next hear any mention of cold temperatures, you will not pull the same face.

Register or login to Leave a Comment.