2.4.1: Pasteurization and Homogenization
Homogenization:
Homogenized milk is fresh milk in which the fat particles are so finely divided and emulsified mechanically that the milk fat cannot separate on standing. The milk fat is forced into tiny droplets. As soon as the droplets form, milk proteins and emulsifiers form a protective film around each one, preventing the fat from reuniting. The tiny droplets stay suspended indefinitely, and milk fat no longer separates and rises to the top as a cream layer. In other words, homogenized dairy products are stable emulsions of fat droplets suspended in milk. It is also said that homogenized milk is more readily digestible.
Prior to the process of homogenization, milk had to be shaken prior to consumption to give it a desirable taste and consistency. This process, which became standard in the 19th century, is a completely mechanical process and does not use any chemicals or additives to achieve. The goal is to evenly distribute the fat that is naturally found in milk to create a homogenous mixture that will not separate when left to stand.
Image: Lizz Daniels, RDN, LD
Pasteurization:
Pasteurization of milk was developed in 1859 by the French chemist Louis Pasteur. This video is provides a brief overview of the history of development of the process in a humorous yet factual way:
Milk can be pasturized using a combination of either high or low temperatures with varying time controls. Given the growth of technology and market desires for milk that lasts longer there are two main types of pasteurization used today. Below is a outline of the two types which also include Ultra High Temperature (UHT).
The two main types of pasteurization used today are high-temperature, short-time (HTST, also known as “flash”) and higher-heat, shorter time (HHST). Ultra-high-temperature (UHT) processing is also used.
- High-temperature, short-time (HTST) pasteurization is done by heating milk to 161°F (72°C) for 15 seconds. Milk simply labeled “pasteurized” is usually treated with the HTST method.
- Higher-heat, shorter time (HHST) milk and milk products are pasteurized by applying heat continuously, generally above 212°F (100°C) for such time to extend the shelf life of the product under refrigerated conditions. This type of heat process can be used to produce dairy products with extended shelf life (ESL).
- Ultra-high-temperature (UHT) processing holds the milk at a temperature of 284°F (140°C) for four seconds. During UHT processing, milk is sterilized rather than pasteurized. This process allows milk or juice to be stored several months without refrigeration. The process is achieved by spraying the milk or juice through a nozzle into a chamber that is filled with high-temperature steam under pressure. After the temperature reaches 281°F (140°C) the fluid is cooled instantly in a vacuum chamber and packed in a pre-sterilized, airtight container. Milk labeled UHT has been treated in this way.
Please watch this short video on the two processes. Please note that this is a branded video and I do not endorse any particular product. This video however, is a clear and concise explanation of pasteurization: