Water blanching is a thermal pre-treatment in which vegetables are immersed in hot water at a controlled temperature for a set time to inactivate enzymes that would otherwise cause quality deterioration during frozen storage.
In trade practice
Processors set water temperature and dwell time based on validated enzyme inactivation studies, typically targeting peroxidase or catalase as indicator enzymes; QA teams verify adequacy using a peroxidase test on finished blanched product. Blanch water accumulates leached sugars and starches over a production run, raising microbial risk and reducing heat transfer efficiency, so water is refreshed or treated at defined intervals. For small or irregularly shaped pieces such as diced carrot or pea, water blanching gives more uniform heat penetration than steam. A common error is overcrowding the blancher, which lowers water temperature and produces under-blanched product.
In a specification
A frozen vegetable specification or supplier quality manual may require documented blanching validation showing time and temperature parameters sufficient to achieve a negative peroxidase result, with records retained per production batch.