What is the purpose of blanching vegetables before freezing?

Blanching is the process of briefly immersing vegetables in boiling water (or steam) for a short, controlled period, then immediately plunging them into ice water to stop the cooking. Its primary purpose before freezing is to preserve the colour, texture, and nutritional value of the vegetables.

During blanching, heat inactivates enzymes - particularly peroxidase and catalase - that would otherwise continue to break down nutrients, degrade colour pigments, and cause off-flavours during frozen storage. Without blanching, frozen vegetables gradually lose their bright colour, develop unpleasant tastes, and suffer significant nutrient loss even at freezing temperatures.

Blanching does not add flavour to vegetables; it is a preservation step, not a seasoning technique. It does not cook vegetables completely - the brief exposure to heat is deliberately kept short to maintain a firm texture. It also does not make vegetables more crunchy; in fact, the brief heat treatment slightly softens cell walls. The crunchiness of properly blanched-and-frozen vegetables comes from the rapid cooling and freezing that follows, which preserves the remaining structure.

Exam tip: The key word linking blanching to its purpose is enzyme inactivation. Enzymes cause deterioration in colour, flavour, and nutrients - blanching stops this process before freezing locks the vegetables in their preserved state.