2. Cooling rate and duration

Cooling rate may be defined as [4]:

$$w = \frac{dt}{d\tau} \text{ [}^{\circ}\text{C/s]} \,, \tag{1}$$

where dt is the temperature variation during the period dτ.

Several assumptions are taken into account in order to obtain the temperature-time function [4]:


The assumption that the sensible heat removed from the product equals the convective heat transfer from the product to the cooling medium leads to [4]:

$$m \cdot c \cdot dt = -\mathbf{S} \cdot h \cdot (t - t\_0) \cdot d\tau. \tag{2}$$

Eq. (2) finally leads to the temperature-time equation:

Food Chilling Methods and CFD Analysis of a Refrigeration Cabinet as a Case Study http://dx.doi.org/10.5772/intechopen.69136 47

$$t = t\_0 + (t\_i - t\_0) \cdot e^{-\frac{b\cdot s}{w\cdot c}t}.\tag{3}$$

The chilling duration is [4]:

cause food poisoning [1]. In these cases, when a longer preservation period is needed, freezing must be used to minimize any physical, biochemical, and microbiological changes affecting quality during storage. The storage life of fresh perishable foods, such as meats, fish, fruits, and vegetables, can be extended by several days by cooling, and by several weeks or months by freezing [2, 3]. During freezing, most of the water content of the meat, about 80%, solidifies

Chilled foods are commonly grouped into three categories, according to the storage tempera-

• �1 to +1�C—fresh fish, meats, sausages and ground meats, smoked meats, and breaded

• 0 to +5�C—pasteurized canned meat, milk, cream, yoghurt, prepared salads, sandwiches, baked goods, fresh pasta, fresh soups and sauces, pizzas, pastries, and unbaked dough;

• 0 to +8�C—fully cooked meats and fish pies, cooked or uncooked cured meats, butter,

In order to chill fresh foods, it is necessary to remove the sensible heat and also the heat generated by the respiratory activity of vegetables and fruits; in animal tissues, aerobic respiration rapidly declines when the supply of oxygenated blood is stopped at slaughter [1, 4].

> <sup>w</sup> <sup>¼</sup> dt dτ ½ �

• at any moment, the temperature is the same in the entire mass of the product;

• there is no mass transfer between the product and the cooling medium.

Several assumptions are taken into account in order to obtain the temperature-time func-

The assumption that the sensible heat removed from the product equals the convective heat

m � c � dt ¼ �S � h � ðt � t0Þ � dτ: (2)

C=s�, (1)

into pure ice crystals, accompanied by a separation of dissolved solids [2, 4].

margarine, hard cheese, cooked rice, fruit juices, and soft fruits.

ture range [1]:

46 Refrigeration

fish;

tion [4]:

2. Cooling rate and duration

Cooling rate may be defined as [4]:

• homogenous product;

where dt is the temperature variation during the period dτ.

• the temperature of the cooling medium is constant;

Eq. (2) finally leads to the temperature-time equation:

transfer from the product to the cooling medium leads to [4]:

$$
\tau\_r = \frac{m \cdot c}{h \cdot \text{S}} \cdot \ln \frac{t\_i - t\_0}{t\_f - t\_0}. \tag{4}
$$
