Steam blanching is a pre-freezing or pre-drying heat treatment in which vegetables pass through a chamber of saturated steam for a controlled time to inactivate spoilage enzymes while minimising leaching of water-soluble nutrients and solids.
In trade practice
Processors set steam temperature and belt speed to achieve a negative peroxidase result across the thickest piece in the batch. Because steam blanching does not immerse product in water, leaching of sugars, vitamins and colour pigments is lower than in water blanching, which matters for premium frozen and dried lines. QA teams validate the process by testing samples from the coldest zone of the blancher. A common error is insufficient dwell time for larger-cut pieces when the same settings are used across multiple cut sizes.
In a specification
A blanching validation record attached to the specification should state steam temperature, belt speed or dwell time, and the peroxidase test result used as the pass criterion for each product and cut size.