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Ultra-high temperature processing and freezing

Article on freezing and ultra high temperature processing.
© EIT Food

You’ve now seen how and why milk is homogenised. Let’s look at another milk processing technique – UHT – and a common way of preserving fresh vegetables – freezing.

Ultra-high temperature processing

Ultra-high temperature processing (UHT) is a food processing technology that sterilizes liquid food, most commonly milk, by heating it above 135 °C over a very short time period – only two to five seconds – to kill microbial spores. UHT milk was first developed in the 1960s and became widely available in the 1970s. A drawback of UHT processing is that the ultra-high temperature can cause browning and change the taste and smell of the milk. However, the process can be optimised to minimise these potential problems or UHT milk can be used as the base for flavoured or coloured milk products which mask these issues. If left sealed, UHT milk packaged in a sterile container has a typical unrefrigerated shelf life of six to nine months, which is a huge gain over pasteurised ‘fresh’ milks. It is perhaps unsurprising that UHT milk is generally more popular in hotter countries where the costs of refrigeration are more significant barriers to the consumption of ‘fresh’ milk. There are quite different attitudes to UHT milk throughout Europe, with its consumption being very common in some countries (like Belgium, France, Portugal and Spain), yet very rare in others (like Denmark, Greece, Ireland, Norway, Sweden and UK).


Why are frozen peas so popular? The sugars in peas turn into starch as soon as they are picked and after as little as one day, they can become grainy and dull tasting. Frozen peas are picked and frozen at the peak of ripeness and immediately flash frozen, halting the process of sugars turning to starch. Frozen peas are more likely to arrive at our kitchens fresher and better tasting than those that are freshly picked.

the process for packaging frozen peas consisting of 6 illustrated steps: picking (hand picking pea pod), grading and sorting (pod opening to release peas), washing (peas with water droplets), blanching (two industrial heating chambers, one with a fire on and an arrow indicating transfer to another with a snowflake on), packaging (bag of peas), freezing (bag of peas with snowflake symbol and a blue thermometer

The process for producing frozen peas. ©EUFIC Source
© EIT Food
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How Food is Made. Understanding Food Processing Technologies

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