In this blog post, we will look at the differences between pasteurization and ultra-high temperature processing, which are methods of heat treatment for milk, and examine the advantages and disadvantages of each.
Milk is a food that provides high-quality nutrients for humans. It is rich in various nutrients such as protein, fat, carbohydrates, vitamins, and minerals, and plays an important role in maintaining health. However, if milk is distributed without any processing, i.e., raw milk, there is a risk that harmful microorganisms that cause spoilage and disease will rapidly multiply. For this reason, the milk we normally drink is heat-treated to remove microorganisms.
Heat treatment reduces the number of microorganisms in raw milk, and generally, the higher the temperature and the longer the heating time, the greater the reduction. However, the time and temperature required to eliminate microorganisms vary depending on the type of microorganism, so it is necessary to know the appropriate heat treatment conditions. The D value and Z value are used for this purpose. The D value refers to the time required to reduce the number of microorganisms to 1/10 when heat treating them at a specific temperature. If you want to reduce the number of microorganisms to 1/100 at the same temperature, you need to treat them for twice the D value. The Z value refers to the additional temperature increase required to reduce the number of microorganisms to 1/10 in 1/10 of the time required for a specific D value. Therefore, microorganisms that are more resistant to heat have higher D values and Z values at a given temperature. For example, suppose that 100 microorganisms are heat treated at 63°C. If the number of remaining organisms is 10 after 360 seconds, the D value is 360 seconds.
If the temperature is 65°C when the number of microorganisms is to be reduced from 100 to 10 in 36 seconds, which is 1/10 of the D value, the Z value is 2°C. Based on the principles of the D value and Z value, various methods of heat treatment for crude oil have been developed.
First, there is the “low-temperature pasteurization method,” in which raw milk is heat-treated at 63°C for 30 minutes to remove 99.999% or more of the microorganisms it contains. The low-temperature pasteurization method is effective in removing microorganisms, but it has the disadvantage of taking a long time. The “low-temperature instant pasteurization method” was developed to compensate for this disadvantage.
The low-temperature instant sterilization method involves heat treating raw milk at 75°C for 15 seconds. This method is as effective as the low-temperature sterilization method in removing microorganisms, but the heat treatment temperature is increased and the heat treatment time is shortened to enable mass production of milk. Milk treated by the low-temperature sterilization method or the low-temperature instant sterilization method has a shelf life of about five days when refrigerated.
If the shelf life of milk is to be extended, even microorganisms that are not killed by pasteurization or low-temperature instant pasteurization must be removed. In order to remove even heat-resistant microorganisms, ultra-high temperature processing is used, which involves heating the milk to 134°C for 2 to 3 seconds. Milk processed in this way can be packaged in sterile packaging and stored at room temperature for more than one month.
However, milk treated with ultra-high temperature processing differs slightly in taste and nutritional content from milk treated with low-temperature pasteurization or low-temperature instant pasteurization. Some proteins and vitamins may be lost during ultra-high temperature processing, and a characteristic heat-treated flavor may develop. Consumers are aware of these differences and choose milk based on their preferences. Therefore, milk manufacturers use a variety of heat treatment methods to provide consumers with a wide range of choices. Thanks to these efforts, we are able to consume safer, fresher, and more nutritious milk on a daily basis.
As such, the heat treatment process of milk plays an important role that goes beyond simple hygiene treatment. It is a complex process that involves the removal of microorganisms, the preservation of nutrients, the maintenance of taste, and the extension of shelf life. This allows consumers to consume safer and healthier milk, and the dairy industry continues to evolve.
