How is uht milk prepared

Most of the milk drunk in the United States, Australia, and New Zealand is of the pasteurised variety, says Hilton Deeth, a dairy expert recently retired from University of Queensland. The milk can be stored for many months thanks to the sterilising effect of heat Credit: iStock. However, in many European nations, UHT milk is the norm. This milk is heated to double the temperature — C — for a mere three seconds. The high heat does its work almost instantly, killing all bacteria and most of the bacterial spores that can stand up to lesser temperatures.

Because it's nearly sterile, as long as it is packaged in a container that's aseptic, it will last and last. No bacteria means no spoilage, at least as long as the package is closed.

You can't do just anything to UHT milk, cautions Deeth. It's designed to last at about C, so if it's shipped across the equator on a sweltering ship, or languishes on a dock somewhere in the tropics for a while, some of those remaining spores may come active and cause problems. And peculiar things do happen sometimes to that everlasting milk in its cloistered existence. The reason that happens can be found in the chemistry that goes on during its treatment and which contribute to some of its odd qualities.

With that brief, intense heat comes a change in the milk's proteins. The whey proteins become unravelled, turning into limp strands. The Maillard Reaction, famous for creating the delicious flavours of caramel, perfectly browned toast, and bacon, as well as many other foods, occurs between the milk's proteins and sugars. An array of enzymes also fall apart, although not, crucially, an enzyme called plasmin, unless the milk is pre-treated to eliminate it.

In the s, building on this early food conservation technology, Tetra Pak pioneered its own continuous UHT process and aseptic packaging systems, and so kick-started the growth of the UHT milk segment. In UHT treatment, the goal is to maximise the destruction of microorganisms while minimising the chemical changes in the product. That means finding the optimal combination of temperature and processing time for different types of food. Tetra Pak offers two alternative methods of UHT treatment: direct or indirect.

In direct UHT heating, steam is briefly injected into the product, and this is rapidly followed by flash cooling. The brevity of the treatment makes it possible to achieve very high product quality.

However, the process requires relatively high energy consumption compared to indirect UHT treatment. With indirect heating, the product does not come into direct contact with the heat source, but is instead heated using heat exchangers. What makes this method so cost-effective is that most of the heat energy can be recovered. The shelf life of UHT milk is not limited by growth of microorganisms but instead by physical, chemical and enzymatic changes in the milk, such as browning reactions, cream separation, sediment or gel formation.

Pasteurization kills all pathogenic disease causing microorganisms in the raw milk. To limit the growth of the remaining spoilage micro - organisms, pasteurized milk needs to be kept under chilled conditions throughout the distribution and storage. The shelf life of pasteurized milk depends on the initial load of microorganisms as well as storage temperature but is normally around 7 days. Raw milk refers to the milk produced by cows or other animals without processing.

Drinking raw milk can cause serious diseases, as it can harbour dangerous microorganisms. According to the Food and Drug Administration FDA , between and more than people in the United States became sick from drinking raw milk or eating cheese made from raw milk. For this reason, in many countries, all milk products sold in retail outlets must be pasteurized or UHT treated. In some markets, consumers buy raw milk and boil it at home.

This makes the milk safe to drink but it is hard to control the process to maintain the quality. How long has UHT technology existed? The birth of sterilised treatment as a means of preserving food began in France in the early s. By using higher temperatures and shorter times it achieved the same effect in killing micro - organisms, while being much gentler towards changes to taste and colour of the milk.

Are there any preservatives used in UHT milk? The ultra-high heat treatment used in the production of UHT milk kills all microorganisms. The milk is then packed in an aseptic package that protects it from entrance of any microorganisms, making it safe for months without need of refrigeration. There is simply no need to add preservatives into a UHT treated product, as there are no microorganisms growing.

Aseptic containers also protect the product from air and light, thereby protecting the product quality. Does UHT milk taste different from fresh milk? And why? UHT milk may taste slightly different from pasteurized milk due to the treatment at a higher temperature.

The taste of UHT milk is often described to be more cooked, richer and creamier compared to pasteurized milk. But the difference is minor when the milk is served at the same temperature - some people may notice while others do not.