What decides the result in vegetables is the blanching that comes before freezing. Enzymes go on causing loss of flavour, colour and texture in frozen product, and a short exposure to hot water or steam stops them. Time depends on the vegetable and the piece size. Underblanching stimulates the enzymes and is worse than none; overblanching costs flavour, colour and vitamins.
The order runs like this:
- Wash and sort, and make the pieces equal; equal pieces mean equal time.
- Blanch in boiling water; in steam the time is about 1.5 times longer.
- Cool for as long as the blanching took, in water at about 15 °C or below or in iced water; if skipped, the vegetable keeps cooking.
- Drain thoroughly, since surplus water lowers quality.
- Spread in a single layer on trays with an air gap between pieces and blast freeze.
In fruit, browning is mostly held back with ascorbic acid or syrup instead of blanching; apple slices can also be steam blanched for 1.5 to 2 minutes. Small fruit frozen in a single layer on a tray and packed once frozen stays loose. Check the result by thawing a few pieces: do they separate, are colour and texture held?