Microwave blanching of vegetables in air pressurised vessel - prior to dehydration, for use as garnish in dried soups etc.

摘要

Blanching is carried out in a vessel holding air at 0.5 - 3.0 bars, the prod. being smothered in its own exuded moisture. The prod. is submitted to microwave or very short wave radiation to provide heat energy for blanching. After blanching the prod. is dehydrated, pref. by vacuum freeze-drying. The installation is pref. designed to operate in alternative frequency bands, viz. 2450 plus-or-minus 50 MHz and 915 plus-or-minus 25 MHz. The prod. is pref. processed in the vessel for 4-10 mins. Vegetables are pref. processed in plastic trays which are permeable to microwaves. The vegetables are spread in a layer in the tray, the layer thickness being 2-3cm., for radiation at a frequency of 2450 MHz and 7 to 10 cm for a frequency of 915 MHz. Compared with steaming or boiling, microwave heating under pressure offers a prod. in which the dehydrated vegetable retains a higher proportion of dry matters. Over very long periods, the microwave treated vegetables exhibited better colour, freshness and tenderness.