Types and techniques of food freezing

Freezing allows food to be preserved for much longer periods of time of its natural life while preserving its flavor and most of its nutritional properties. This technique has been used for years to preserve perishable goods, but it has not been until a few years ago, thanks to industrial development, when different freezing techniques appropriate for different uses have appeared.

WHAT HAPPENS WHEN YOU FREEZE A FOOD?

Before starting to talk about the different techniques, it is convenient to know what happens when freezing a food, since that will allow us to better understand their differences and why each one is appropriate for a circumstance.

When we freeze a product, what we are doing is freezing the water that contains it. At the cellular level, freezing acts on water that is linked to lipoproteins, proteins and other components. This water freezes forming small crystals, while the rest of the components remain practically unchanged.

FAST FREEZING VS. SLOW FREEZING

Within the types of freezing, they can be classified by the speed at which food is frozen and by the method. While it is true that depending on whether it is fast or slow freezing, some techniques or others will be used, it is important to clarify what each speed consists of and how each one affects the properties of the food.

Rapid freezing causes the ice crystals that form to remain within the cellular structure and be small in size. This means that they do not deform the meats, fruits, vegetables and other frozen products: they keep their shape, flavor and properties intact.

When freezing is slow, the water from the intercellular spaces freezes earlier and, due to its expansion, presses on the extracellular fluid, causing the nutrients to be concentrated and the water to come out. This causes the ice crystals to be much larger, leading to dehydration, cell membrane rupture and denaturation of proteins found inside cells.

Rapid freezing is done within 5 to 60 minutes and uses fluids to aid cryogenization.

Although both techniques are effective, they are used for very different functions. Slow freezing is appropriate for preserving large amounts of food in cold rooms such as meats. Cryogenization or rapid freezing is used in kitchens and in the food industry.

There is also an intermediate process called medium freezing in which, through cold tunnels, food is frozen at the rate of 1 – 5 cm per hour.

FOOD FREEZING TECHNIQUES

Each freezing speed corresponds to a different type of technique that will help carry out the process respecting the structures of the food and ensuring that nutritional quality and flavor are maintained. There are three main freezing techniques:

· By air

It consists of a flow of cold air through which heat is extracted from the product until it reaches the final temperature. This type of technique is found in many of the chambers and freezing tunnels, which use circuits cooled with CO2, ammonia or glycol to cool the chambers to the desired temperature. This type of technique is mainly used for slow and medium freezing.

· By contact

A very cold surface is used as plates with metal sheets at a very low temperature that, through contact with the product, manage to eliminate its heat until it freezes. This type of technique is widely used to freeze seafood and fish.

· Cryogenization

This method is used in rapid freezing and, using liquid nitrogen or carbon dioxide to achieve maximum crystallization in a time never exceeding 2 hours. Neither nitrogen nor CO₂ is harmful applied to food. They also do not leave smell or taste in them. The food is introduced or sprayed with these substances and, once it evaporates it takes the heat with it. This process is also called deep freezing and, although it is the fastest and most efficient, it is also the one with the highest cost.

Regardless of its type of freezing and the technique used, each type of food needs to be made under the appropriate conditions to avoid transformations in its cellular structure that affect its properties and taste.

During the storage of food, it should be taken into account to:

1. Keep the cupboard clean and tidy.

2. Do not store food directly on the floor of the cellar but on pallets or shelves in sanitary material.

3. Perform vector control.

4. Check the temperatures of the refrigeration unit or pantry and keep a daily record.

5. Make sure there are minimal temperature variations during the storage process.

6. Do not open the freezer doors for a long time or constantly, because this helps to maintain the appropriate temperature and saves energy.

7. Do not overfill refrigerators or freezers because they hinder cleaning and hinder the circulation of cold air. The clogging of fans should be avoided.

8. Food should be kept in order inside the refrigeration chambers, and freezing, etc. Separate meats according to their species: beef, chicken, pork, etc.

9. Ready-to-eat products such as sausages, tamales, etc., physically separate them from raw meats inside refrigerators, freezers, displays and dispensers.

10. Avoid putting in contact, cooked or ready-to-eat products without prior cleaning and disinfection, of equipment, utensils and tables that have been used for raw foods.

11. Do not keep hot food in refrigeration, as it would raise the internal temperature of the refrigerator, which stimulates bacterial growth.

12. Freezers should always be at -18°C or less. 

13. Protect food to prevent freezing burns using special sachets and plastic containers.

14. Do not introduce hot food into the freezer as it would increase the temperature of the freezer adversely affecting other foods. Let the food cool before freezing.

15. Make sure frozen foods have been completely thawed before cooking.

16. Food that has been frozen and thawed should never be re-frozen.

17. Inspect, label and date the food that is stored, use the METHOD of rotation of goods PEPS (First entries first outputs).

18. The area where dry foods such as canned foods, cereals, flour, sugar, biscuits, coffee, tea, and other non-perishable foods are stored should be in a dry, cool, well-ventilated area protected against insects and rodents.

19. Avoid cross-contamination during storage. Bacteria can pass from one food to another by direct contact, or through surfaces in contact with them.

*Source SARRIFER // RINCÓN DEL VAGO