Blanching is a cookery technique used in varying ways, but all involve placing the item being blanched into boiling water or in the case of french fries, hot oil.
To blanch actually means to whiten, but not all fruit or vegetables will be affected this way.
The method is often to place fruit or vegetables into boiling water, for a short predetermined amount of time and then removed and plunged into iced water to stop the cooking process.
Blanching is used to soften food, or partly or fully cook it, or even remove the strong flavour from it as with cabbage or onions.
For example, in our article about almonds, blanching is used to soften and remove the brown seed skin on the almond.
With tomatoes, once the skin is scored, the tomato is blanched as above, which after being cooled in the ice bath, allows the tomato to be peeled easily.
Asparagus spears are cooked in this way, placed in boiling water for 30 seconds to cook them and immediately cooled in ice water to stop the asparagus over cooking and going limp and discoloured.
“Shocking” the vegetables in this way in the ice bath helps them retain their vibrant colour.
This is different from parboiling, where the ingredients are not shocked.
In frying, blanching can be used as a term for pre-cooking chips or french fries in oil. The advantage of this is that the potato is cooked in the blanching and when the order is placed they are fried again at a higher temperature to crisp up the out side of the chip.
Vegetables are blanched prior to freezing. The blanching in boiling water or steam stops the enzymes which cause decay from working whilst the vegetables are frozen, aiding the retention of colour and flavour as well.