Throughout many Asian countries, water chestnuts are prized for their ability to retain a snappingly fresh crunch, even after they have been cooked. They are neither nuts, nor are they related in anyway to chestnuts. They are actually the underwater corm of two varieties of water grass Eleocharis dulcis and E. tuberosa. Water chestnuts are also an extremely prolific crop, yielding well over 2000 kg per hectare
The chestnut association comes from the similarity the corm bears to chestnuts, although water chestnuts are more symmetrical and have a light brown papery protrusion at the top where the grass was attached. Whole water chestnut corms are between 30 – 50 mm in diameter, and have a deep brown coloured skin, which has a glossy appearance, reinforcing the chestnut comparison.
Water chestnuts are most often found canned, but try visiting an Asian market to procure fresh specimens, as their flavour and texture are appreciably superior. To deal with whole water chestnuts, simply take a small sharp knife and peel away the dark brown outer skin until you have reached the ivory center, or the "nut". These are now ready to be used raw in salads or sliced and tossed through stir fried dishes, providing a tantalizing crunch.
The flavour of water chestnuts can only be referred to as mild, but they have an enchantingly subtle sweetness and a slightly "nutty" flavour, somewhat reminiscent of wild rice, another water grass.
Apart from whole water chestnuts, other culinary uses include water chestnut flour, which has similar thickening properties to cornflour (cornstarch). The difference is water chestnut flour leaves a shimmering gloss once cooked, while cornflour results in a dull opaque finish to soups and sauces.
In Thailand a favourite way to cool off from the heat is to partake in a delightful dish called tup tim krob. This is tiny dice of water chestnut flavoured with various essences such as jasmine and rose, then sweetened with sugar. These are mixed with coconut milk and shaved ice to create a unique sweet snack.
destrius’ mentions that water chestnuts are made into an unusual but cooling drink in Asia. They are either blended raw, or boiled with a little palm sugar then pureed into a drink.
achan makes a good point. Fresh water chestnuts can be hard to find in smaller towns, and tinned water chestnuts are quite bland. He suggests improving the flavour by soaking them in sugar water for a while. Simply dissolve a few spoons of sugar in 1 cup (250 ml) of warm water and submerge the water chestnuts for 20 minutes or so. Drain and proceed with your recipe.
One of the more intriguing non-culinary uses for water chestnuts occurs in China. Apparently inquisitive and slightly dim children who swallow coins are fed water chestnuts as a purgative. Do not try this at home.