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Things that affect Milk Freezing

Q: Why does milk not freeze in a normal freezer? Is there any scientific reason behind it?

Krishna: Several things influence freezing of liquids.

The freezing point of milk is an important indicator of the milk quality. Freezing point of milk is one of the quality parameters, which detect natural quality of milk, and it is used for water content detection in milk. The number of compounds that can enter milk by contamination is endless. Therefore, the Freezing point of milk is influenced by factors related to variation in environment, management, and breed (1,2).

More wide and deep spectrum of factors: stage of lactation, age, health status, breed, milk yield, feed quality and amount, season, region, milking time and others (3).

The most significant factor affecting freezing point of milk is water addition. Freezing point of a solution depends on the number of particles in the solvent (water phase of milk), rather than the kind of particles. Water without solutes will freeze at zero degrees C. The presence of any solutes will depress freezing point below zero degrees C. The freezing point of milk depends upon the concentration of water-soluble components. As milk is more diluted, the freezing point will rise closer to zero (4).

Research also shows that not only extraneous water presence in milk affects the freezing point of it. But there are other factors such: milk constituents that are present in genuine milk. Their concentration may be influenced by a number of factors, including dairy cow breed, stage of lactation, subclinical mastitis, dairy cow’s nutrition, water intake , climatic conditions, regional and seasonal influences, the concentration of lactose and pH of milk, carbon dioxide concentration in milk (3).

Other components contributing include in decreasing importance: potassium 12.7%, chloride 10.5%, sodium 7.2%, citrates 4.3%, urea 1.9% and other components 6.9%. Freezing point depends on the molar concentration of these soluble, low-molecular weight compounds (5).

The cooling or heating of milk causes aggregation of soluble salts and their transfer to casein micelles or fatty globules. This reaction is, however, revisable and the freezing point may therefore vary depending on the time and temperature of analysed samples (6).

There are different substances, which can be added to milk with the main purpose to prolong shelf-life of raw milk in another way. There are detergents, preservatives, formaldehyde, sodium carbonate, and hydrogen peroxide. Antibiotics and other drugs are widely used to treat cows with mastitis or other infections or ailments. When a cow is treated, its milk is generally withheld from the bulk tank until treatment stops and milk is free of drug residues (3).

The freezing point of cows’ milk is relatively constant as a consequence of osmotic equilibrium in milk and blood.

According to the research results, the freezing point of milk has a wide range. Chemical composition of milk has an influence on it, still it is known that milk typically consists of approximately 87% water or 13% total solids. It is noteworthy that the freezing point of milk is altered when water concentration varies, meaning that if the product has a higher concentration of total solids it can be changed too(3).

When so many things can be present in milk, the freezing point also varies from milk sample to milk sample like skimmed milk to, pasteurized milk and to milk with different substances (formaldehyde, antibiotics, sodium carbonate, hydrogen peroxide, disinfectant, and detergent) in different concentrations.

Your whole milk doesn't freeze as well as semi-skimmed because of its higher fat content. This is due to fat requiring a much lower temperature than the -18 degrees that typical household freezer can offer.

However, as I use very low fat milk, my milk freezes in my fridge freezer.

Footnotes:

1. M. Henno, M. Ots, I. Jõudu, T. Kaart, O. Kärt, “Factors affecting the freezing point stability of milk from individual cows”, International Dairy Journal, vol. 18, 2008, pp. 210–215.

2. G. E. Mitchell, “The contribution of lactose, chloride, citrate and lactic acid to the freezing point of milk”, Australian Journal of Dairy Technology, vol. 44, pp. 61–64, 1989.

3. Evaluation of Factors Affecting Freezing Point of Milk - Zenodo

https://zenodo.org › record › files

4. F. Harding, Milk quality, An Aspen Publication, Gaithersburg, 1999, pp. 62–67.

5. B. A. Slaghuis, „The freezing point of authentic and original farm bulk tank milk in the Netherlands”, International Dairy Journal, vol. 11 pp. 121–126, 2001.

6. J. W. Sherbon. “Physical properties of milk”, In Fundamentals of Dairy Chemistry, N. P. Wong, R. Jenness, M. Keeney, E. H. Marth, Van Nostrande Reinhold Ed. New York, pp. 409–460, 1988.

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