Freezing point of foods

Before proceeding, it is worth noting that at temperatures below freezing (i.e., below the freezing point of food, in the presence of an ice phase), the definition of aw changes to (Fennema, 1996)... 

To increase the boiling point or reduce the freezing point of foods ... 

As a general rule, foods which are not to be frozen are handled and stored at a temperature just above their freezing point, providing this does no damage (exceptions are fruits such as bananas and lemons). Produce which is to be frozen must be taken down below the freezing point of the constituents. Since foodstuffs contain salts and sugars, the freezing process will continue down to -18°C and lower. 

Demott, B. J. 1966. The freezing point of milk produced in four markets in Tennessee. Milk Food Technol 29, 319-322. 

Demott, B. J., Montgomery, M. J. and Hinton, S. A. 1969. Influence of changing from dry lot feeding to pasture on the freezing point of milk. J. Milk Food Technol. 32, 210-212. 

Freeman, T. R., Bucy, J. L. and Kratzer, D. D. 1971. The freezing point of herd milk produced in Kentucky. J. Milk Food Technol. 34, 212-214. 

Suppose we move back to solid at point (355 torr and - 10°C). If we now hold the temperature at — 10°C and reduce the pressure, we move vertically down along EJ. At a pressure of 2.1 torr we reach the suhlimation curve, at which point the solid passes directly into the gas phase (sublimes) until all the ice has sublimed. An important application of this phenomenon is in the freeze-drying of foods. In this process a water-containing food is cooled below the freezing point of water to form ice, which is then removed as a vapor by decreasing the pressure. 

It has been proposed that the absorption of ultrasound energy depends on the thermo-elastic relaxation of ice crystals in food and is affected by ice crystal orientation and size, impurities present in the ice crystals, as well as temperature (Kissam et al., 1981). Miles and Shore (1978) and Shore et al. (1986) found that ultrasound was more attenuated in frozen meats than in unfrozen tissues and that the attenuation increased markedly with temperature, reaching the maximum near the initial freezing points of the foods before decreasing rapidly at higher temperatures, thus making ultrasound particularly suitable for the controlled thawing of foods (Miles et al., 1999 Torley and Bhandari, 2007). 

Butylated hydroxytoluene (BHT) is used as an antioxidant in processed foods. (It prevents fats and oils from becoming rancid.) A solution of 2.500 g of BHT in 100.0 g of benzene had a freezing point of 4.880°C. What is the molecular weight of BHT ... 

Kan, B., 1962. Methods of determining freezedrying process end-points, in Freeze-drying of foods (ed. F. R. Fisher). National Academy of Sciences - National Research Council, Washington, D. C., USA, pp. 163-177. 

Rustad, T., Strommen, 1., 2007b. Relations between product structure, sorption characteristics and freezing point of atmospheric freeze dried foods. Drying Technol. 25(5) 853-865. 

The boiling and freezing points of 2,3-BD are 180-184 °C and —60 °C, respectively. It is either a colorless liquid or in crystalline form. It can be dehydrogenated to diacetyl, a highly valued flavoring agent in food products (Syu 2001). It can also be dehydrated to methyl ethyl ketone, which has uses as a liquid fuel additive and a solvent. The levo-form of 2,3-BD has potential use... 

Sodium chloride, an ordinaiy salt (NaCT), is the least expensive per volume of any brine available. It can be used in contact with food and in open systems because of its low toxicity. Heat transfer coefficients are relatively high. However, its drawbacks are it has a relatively high freezing point and is highly corrosive (requires inhibitors thus must Be checked on a regular schedule). 

The freezing of a product in the vacuum chamber by the evaporation of 15-25 % of its water would reduce the process time, the investment- and the operation cost, since the evaporation of this water could be done in a very short time, and no extra freezing installations are required. Oetjen [4.4, 4.5] points out, that this process has substantial disadvantages for the quality of the product and is only applicable for a limited number of products. Therefore this process is no longer used (see Section 2.1.5). The freezing processes for food are discussed in the Sections 2.1.1 and 2.1.3, and the possible freezing rates in Section 1.1.1. The decisive quantities for the freezing rastes are ... 

It is important at this point to make the distinction between the terms freezing and frozen storage. The former may be regarded as part of the primary manufacturing process and uses, for example, fluidized bed freezers or plate freezers depending upon the nature of the food to be frozen. Frozen storage refers to the storage of food at... 

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