High pressure processing
High pressure can be used not just to pasteurise food products, but also to change their characteristics - as this video clip demonstrates.
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High pressure processing uses pressures of 100 to 600 MegaPascals for up to 5 minutes to decontaminate foods, or change their functional properties.
This pilot scale system has a volume of about 800 millilitres. Industrial equipment can process over 500 litres at a time.
To pasteurise products such as grapes, the product is placed in the vessel and the lid is closed. The pressure is increased by pumping fluid (usually water) into the vessel through a one way valve. This can take a few minutes.
Once the required pressure is reached, it is maintained for the required time, usually 1 to 5 minutes.The process results in a small temperature increase – about 3 degrees Celsius per 100 MegaPascals of applied pressure, although this varies depending on the product. The temperature returns to its initial value once the pressure is released, and the process is essentially non-thermal.
The pasteurised grapes are similar to the raw material in terms of appearance, taste, texture and nutritional value.
As well as pasteurising, high pressure processing can be used to modify the properties of ingredients through protein denaturation. As an example, it can be used to induce texture changes in eggs.
As before, pressure is applied for a short period of time, and there is a small rise in temperature, but this is not significant in the modification of the egg.
After decompression the temperature returns to its original value.
By denaturing the egg yolk proteins, high pressure processing results in the yolk having a soft margarine-like texture.