Pasteurization is the process of heating milk up and then quickly cooling it down to eliminate certain bacteria. For effective pasteurization, milk can be heated up to 145 degrees Fahrenheit for 30 minutes, but this method isn’t very common. More common is heating milk up to at least 161.6 degrees Fahrenheit for 15 seconds, which is known as High-temperature Short-Time (HTST) pasteurization, or flash pasteurization. This method will keep milk fresh for two to three weeks. Then there’s Ultra-Heat Treatment (UHT), whereby milk is heated to 280 degrees Fahrenheit for a minimum of two seconds. This processing results in a shelf life that can extend up to nine months. Milk treated with pasteurization or HTST is labelled as “pasteurized,” while milk treated with UHT is labelled as “ultra-pasteurized.”
The Purpose of Pasteurization
- To increase milk safety for the consumer by destroying disease-causing microorganisms (pathogens) that may be present in milk.
- To increase keeping the quality of milk products by destroying spoilage microorganisms and enzymes that contribute to the reduced quality and shelf life of milk.
Homogenization is an entirely separate process that occurs after pasteurization in most cases. The purpose of homogenization is to break down fat molecules in milk so that they resist separation. Without homogenization, fat molecules in milk will rise to the top and form a layer of cream. Homogenizing milk prevents this separation from occurring by breaking the molecules down to such a small size that they remain suspended evenly throughout the milk instead of rising to the top.
Homogenization is a mechanical process and doesn’t involve any additives. Like pasteurization, arguments exist for and against it. It’s advantageous for large-scale dairy farms to homogenize milk because the process allows them to mix milk from different herds without issue. By preventing the cream from rising to the top, homogenization also leads to a longer shelf life of milk that will be most attractive to consumers who favour milk without the cream layer. This allows large farms to ship greater distances and do business with more retailers. Finally, homogenization makes it easier for dairies to filtrate out the fat and create two percent, one percent and skim milk.
While it is possible to have pasteurized milk that hasn’t been homogenized and homogenized milk that hasn’t been pasteurized, most milk found in U.S. supermarkets have undergone both processes. If they are to occur together, milk is typically pasteurized first and then homogenized, because the heat from pasteurization makes fat molecules easier to break down for homogenization.