Refrigeration

In refrigeration, cold is applied to bring the temperature down to between +0 and +4°C (these are the normal values). With refrigeration, most of the micro-organisms slow down their vital functions and, consequently, also slow down the biochemical reactions that bring about changes in the product. Reactions of a chemical nature are slowed down by refrigeration too, so that the freshness of produce can be maintained longer than with ordinary ambient temperatures.

Freezing

In freezing, cold is applied with such intensity as to very quickly lower the temperature down to a level of inhibition of both microbial and biochemical and enzymatic activity.
The standard freezing temperature is -18°C, with an admitted tolerance of approximately 3°C higher for transportation or to keep the product in refrigerated counters for display and sale.
Freezing causes the product to solidify, since all the water molecules it contains crystallize. The properties of water crystallization determine the technological quality of freezing: fast freezing enables obtaining very small ice crystals that do not break the cell walls and, consequently, do not damage the tissues and texture of the product which, unfrozen, will regain its original physical properties.
If freezing takes place slowly, the ice crystals formed inside the cells and tissues are larger, with sharp corners that inevitably damage the cell walls, breaking them; when the product is unfrozen, the liquid component is lost and the product loses its firmness. Its nutritional besides its organoleptic properties are impaired as well.
When freezing, speed is therefore fundamental. The speed of freezing must permit quickly reaching the temperature of -18°C throughout the product.
The graphs published show these concepts visually.

CRYOGENIC GAS DEEP-FREEZING

Freezing in practice

The first problem encountered by a frozen fresh pasta production company is the type of facility to use to freeze its product. This choice is made by taking into account the following requirements:

Nitrogen (N) and carbon dioxide (CO₂) are supplied by companies that in many cases lease freezing plants as well. No matter how you are planning on freezing it is necessary to have a tank to contain the gas. This tank must be different if you use nitrogen instead of carbon dioxide, given the different properties of these two gases (nitrogen must be kept at a temperature of -196°C, whereas carbon dioxide at -70°C).
The dimensions of the tank vary from 5,000 to 20,000 litres. If you are planning on freezing with the IQF method it is necessary to have a tunnel freezing system, which may be linear, Jiro-freezer, or by gravity with belts.
The most common ones are the belt tunnels that can have a capacity varying from 150 to 400 kg/h.
If you are planning on freezing with the Block Freezing method, it is necessary to have a static cell. This type of freezing is used when it is either not necessary or not possible to freeze with IQF, and therefore when freezing ready-to-eat dishes. Block Freezing is common for ready-to-eat dishes (lasagne, cannelloni, pre-cooked long pasta such as spaghetti and tagliatelle), especially in medium and/or medium-small production plants.

Air freezing

Air freezing takes place by means of systems that generate cold by means of mechanical refrigerators, using therefore electricity or diesel engines. The chart in Table 1, referring to the distinction between IQF and Block Freezing, can be applied to air freezing as well, with the variations given in Table 2.

The choice between nitrogen or carbon dioxide freezing and freezing with mechanical refrigerators, considering for example freezing with IQF, is essentially based on the parameters summarized in the last table (Table 3). This table shows the Italian situation, which moreover can be taken as reference for other local situations within an international framework as well.

In conclusion, it may be stated that the choice between a freezing plant with mechanical refrigerators compared to a gas system is essentially based on the answers to questions 2) and 3) asked at the start, and hence:

1. If there is the possibility of producing considerable volume, such as to justify a fairly heavy financial commitment such as the purchase of a mechanical refrigerator freezer, there is unquestionably a saving which increases as production increases.
   

2. If there is the assurance of continuous production, it is anyhow worthwhile passing on to mechanical refrigerator freezing. In the case of non-continuous freezing (for example, six months a year), it is much less expensive to pay a low lease rather than higher financial leasing or loan instalments.

* The data in the tables have been calculated referring to the Italian market. The values given may moreover be taken as reference for other local situations that are similar or anyhow comparable to them, also within an international framework