Under vacuum, due to a negative pressure, the moisture in the food evaporates rapidly in the hot oil at a lower vaporization temperature, therefor, the fruit and vegetable chips is of a porous and firm texture.
The edible oil in the vacuum low-temperature frying process is not only a heat transfer medium for dehydration, but also an important ingredient to change the flavor of food. Therefore, vacuum frying is an organic combination of dehydration drying and frying seasoning.
Oil temperature is an important factor affecting dehydration rate, flavor, color and nutrition of food.
The oil temperature is usually controlled so that the oil has a low viscosity and corresponds to the degree of vacuum. The variety of fruits and vegetables, as well as the thickness of the slice is various; the frying temperature should be adjusted differently.
The degree of vacuum is related to the frying temperature and frying time, also depends on the performance of the vacuum pump. It has a significant effect on the quality of the fried vegetable chips.
The higher vacuum degree and the proper oil temperature cannot only prevent the phenomenon of boiling and the deformation of the fruits and vegetable chips, but also shorten the frying time, and can complete the operation under a perfect vacuum without extra adjustment.
The vacuum of various fruits and vegetables during frying is not all the same. Higher vacuum is beneficial to improve the natural color and deoiling performance of the chips.
In addition, the pre-treatment processing of fruits and vegetables slice before vacuum frying is also essential.
This includes blanching process for enzyme inactivation to keep the original color and flavor, soaking process to increase solid content, thereby, improving tissue texture, and a quick freeze process to improve the crispness, and reducing the oil uptake.