Milk naturally contains a unique package of nutrients that are essential for good health, including high quality protein, calcium, B vitamins, potassium and phosphorus to name a few.
Even better, it comes in a range of convenient formats to suit your needs – from fresh, refrigerated milk to long life UHT milk and milk powder. But what effect, if any, does processing have on all that great nutrition in milk? Let’s find out by exploring the different processes in a little more detail.
"So, whether you prefer the fresh taste of milk straight from your supermarket fridge or you enjoy the convenience of UHT milk or milk powder, processing does not significantly change the goodness that milk provides."
Homogenisation is a process where milk is passed under pressure through very small nozzles to break up the fat into smaller droplets. This ensures that the cream in milk doesn’t separate and rise to the top when the milk is stored in a bottle or carton. Homogenisation doesn’t significantly change milk’s nutrition.
Pasteurisation typically involves heating milk to at least 72C for around 15 seconds, before cooling quickly to 4C. Pasteurisation is a legal requirement for all milk for retail sale in New Zealand and ensures that milk is safe to drink by destroying potentially harmful micro-organisms.
Conservative heat treatment like pasteurisation doesn’t substantially change the nutritional value of milk. The macronutrients (protein, fat and carbohydrate), minerals (e.g. calcium and phosphorus) and fat soluble vitamins (e.g. vitamin A, vitamin D) are very heat stable so their levels are not affected by pasteurisation.
Some water soluble vitamins including B vitamins can be less heat stable compared to other nutrients. However, the most significant B vitamins in milk are riboflavin (vitamin B2) and vitamin B12 and both of these B vitamins have good heat stability. Riboflavin levels are unaffected and less than 10% of vitamin B12 is lost following pasteurisation.
UHT typically involves heating milk to at least 135C for a shorter time – usually around four seconds. It enables milk to stay high quality for longer, giving it a longer shelf life and enabling it to be stored in the cupboard until opened. Like with pasteurisation, most of milk’s nutrients are largely unaffected by UHT, meaning that UHT milk still contains almost the same nutrition bundle as fresh milk, with the exception of some B vitamins which may be a bit lower. Of the main B vitamins in milk, there can be greater losses of vitamin B12 compared to pasteurisation (10-20%), although this can be affected by how long the milk is stored for. Riboflavin levels are not affected by UHT.
Spray drying is used to make milk powder and enables milk to be stored and enjoyed for much longer than liquid milk. Milk is sprayed into a fine mist allowing the water to evaporate, creating a soft, fine, white powder. A lot of care is taken to ensure this process is as gentle on the milk as possible. This means that spray dried powder retains around 90% of the riboflavin found in fresh milk, and at least two thirds of the vitamin B12, with all the other major nutrients being largely unchanged.
So, whether you prefer the fresh taste of milk straight from your supermarket fridge or you enjoy the convenience of UHT milk or milk powder, processing does not significantly change the goodness that milk provides. You can be sure you’re still getting a great source of high quality nutrition, with all of them counting as one of your 2-3 serves of dairy a day.