Milk powder is more economical than whole milk yet it has the same nutritional value.
ANSWER: Processing milk into powder has little effect on its food value. Milk contains many useful nutrients, such as B vitamins and calcium.
Whole (full-cream) milk is about 87% water, and skim milk about 91%. The goal in producing milk powder is to remove that water while retaining all the desirable properties of the milk, namely colour, flavour, solubility and nutritional value.
The first step in processing milk into powder is to boil it at reduced pressure and a temperature of 45-70°C, which evaporates some of the water. Next, it is sprayed as a mist into 60°C air to remove the remaining moisture and produce powder. At those temperatures, there is minimal thermal damage to the milk and its nutrients.
Milk powder is cheaper than whole milk, so is an economical option for big consumers. Powder is best stored in the freezer, particularly in summer, so the milk fats don’t go rancid.
ANSWER: Most milk goes by tanker from the farm to the factory and is processed, bottled and on a truck bound for the supermarket within 48 hours. So, supermarket bottled milk is fresh, not powdered then reconstituted.
It takes a lot of energy to dehydrate liquid milk, leaving powder with nutrients intact. So why would you, if you can supply fresh whole milk daily to market?
The New Zealand dairy industry accomplishes this year-round feat by dividing milking herds into different calving periods. Most dairy cows have a break from milking in winter, leading up to calving from July to August. This break coincides with slower grass growth.
However, part of the herd calves earlier, usually in April, and these cows keep producing milk through the winter. Because grass growth isn’t as prolific in the colder months, winter-milking cows are given supplemental feed such as silage to enable them to keep producing.
The milk cows produce varies according to many factors, including the season, when they calve and what feed is available. Protein content, in particular, is variable. It is typically higher in autumn and winter and lower in spring and summer.
Some producers standardise their milk by putting it through an ultra-filtration system that separates the protein and fat from the other components, such as lactose, soluble minerals and vitamins. So-called permeate is the parts of the milk – namely lactose, vitamins, minerals and water – that pass through (or permeate) the filter.
Milk processors alter levels of fat in the final milk product, depending on whether the milk is going to be sold as skim, trim or full-fat. They can also standardise the amount of protein in the final milk product by recombining certain levels of permeate with the heavier protein-rich portion of the filtered milk to ensure it meets set protein and calcium targets for the various milk products.
Fonterra’s Anchor milk goes through ultra-filtration and recombining to produce a consistent product throughout the year. It is labelled as “standardised” to indicate it’s gone through this process.
However, not all milk suppliers extract and reuse permeate. Goodman Fielder’s Meadow Fresh, for example, is permeate-free, so it contains naturally varying levels of protein and calcium.
This article was first published in the November 30, 2019 issue of the New Zealand Listener.