Vacuum frying is a method when a food product is deep-fried under vacuum (no pressure) or near-vacuum conditions.
The general method is as follows.
The foodstuff is enclosed into a specialized pressure vessel containing a deep fryer. The vessel is connected to a vacuum pump. After this, the vessel depressurizes. The foodstuff is immersed into frying oil within the vessel, fried for the required time, and then lifted up from the oil. Finally, the vessel is re-pressurized again. Re-pressurization should be done quickly. A centrifugation step can also be inserted for removal of excess frying oil after the frying step before the pressurization. This technique has shown to reduce the amount of fat in the fried product. This might be because of the lower temperature that is needed to boil water and oil under vacuum conditions. The removal of excess fat has shown to be important. A report shows that the optimal time for removal is just after the frying but before the re-pressurization step (centrifuged within the pressure vessel). Also, fast re-pressurization has been shown to be a key factor in reducing the fat content. Although the fat content is reduced, the quality is still maintained and even superior to normal deep-frying in some cases. It should be stated that some reports show an increase in fat content, although these are fewer than those who show the opposite effect.
Apart from the fat-reducing ability, the lowered temperature in vacuum frying may also reduce the formation of acrylamide:
Acrylamide is a possible carcinogenic compound that is produced when protein and reducing sugars are heated above 150°C. Preservation of natural colour and favours. The colour of the finished product is lighter than if the product is fried at atmospheric pressure. As the vessel in which the product is vacuum fried needs time for pressurising and depressurising, the process will take longer time. The pressurisation step is also energy consumption and an increase in energy consumption is therefore expected.
