I read that when cooking root vegetables, you should put them into the water when it’s still cold and bring them to the boil. But I also read that other types of vegetables should be placed in already boiling water. Why?
• For some vegetables, the cooking time needs to be short and fairly precise. This is more easily achieved by plunging them into boiling water.
However, root vegetables take longer to cook. Put them in boiling water, and you risk the outside becoming too soft before the inside is fully cooked. These vegetables benefit from slow heating, during which time an enzymatic reaction takes place, firming them up.
According to the book McGee on Food & Cooking (Simon and Schuster, 2004), certain vegetables and fruits – including potatoes, sweet potatoes, beetroot, carrots, beans, cauliflower, tomatoes, cherries and apples – contain an enzyme in their cell walls that becomes activated at around 50°C and inactivated above 70°C. The enzyme alters the cell-wall pectins, making them more resistant to being removed or broken down at boiling temperatures.
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“The usual rule is that if a vegetable is harvested from under the ground, then you boil it from cold“
The usual softening that occurs during cooking can therefore be reduced by heating initially to a modest temperature. During this time, the foods develop a persistent firmness that survives subsequent prolonged cooking.
This is also why root vegetables do not do well in slow cookers – they can spend too long in the initial “pre-cooking” zone and go firm in a way that isn’t reduced by further cooking. Pre-boiling them for a few minutes before they go into a slow cooker inactivates the enzyme and allows them to soften during slow cooking.
David Gibson, Leeds, West Yorkshire, UK
• Ignore all such advice and steam your vegetables. That way you minimise the loss of nutrients that would otherwise leach out into the water.
David N. Cox, Senior Research Scientist, CSIRO Food and Nutrition Flagship, Adelaide, South Australia
• The usual rule is that if a vegetable is harvested from under the ground, then you boil it from cold. If it is from above the ground, it should be plunged into boiling water.
If, however, it is from “underground, overground” then it’s a Womble, and you probably shouldn’t be cooking it.
Mike Vose, Ashton-under-Lyne, Lancashire, UK
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This article appeared in print under the headline “Rooting out trouble”
