What is a Water Chestnut Anyways?

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My wife and I recently got some Chinese takeout from one of our favorite local places (mostly because they’re the only one that delivers), and my wife, hating water chestnuts, was complaining about them in her dish.  This got me wondering what exactly is a water chestnut?

There actually happen to be a number of different plants that produce what we call water chestnuts.  You can find things labeled as water chestnuts throughout Europe and Asia but, being that we’re talking Chinese takeout, we’ll focus on the Chinese water chestnut.

Chinese water chestnuts come from the corms of a sedge.  Don’t know what either of those terms mean?  Neither did I so I looked them up.

A sedge superficially resembles grass.  There are some 5,500 known species of sedges, the most notable being the papyrus sedge, from which the Ancient Egyptian writing material was made, and the Chinese water chestnut.  A corm is a bulbo-tuber, or bulbotuber, which is a short, vertical, swollen underground plant stem that serves as a storage organ used by some plants to survive winter or other adverse conditions such as summer drought and heat.

If all that was still a little too complicated, think aquatic grass like plant with a potato like thing attached to its roots.

The Chinese water chestnut is native to Asia, Australia, tropical Africa, and various islands of the Pacific and Indian Oceans.  It is grown in many of these countries for its edible corms (aka the potato like thing).

This crop can be cultivated in paddies, like the rice paddies you commonly see in pictures of Asia (see below for picture).

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As Chinese water chestnuts are an aquatic plant,  they should always be ubmerged in approx. 10 cm of water.  The crop needs continuously high soil temperatures, ideally 14-15.5 °C (or 57.2-60ºF).  At 13.6 °C (56.5ºF), the corms begin to sprout.  The soil for growing Chinese water chestnuts is ideally a sandy loam.  The plant produces two types of subterranean rhizomes (a modified subterranean stem of a plant that is usually found underground, often sending out roots and shoots from its nodes).  Under long-daylength conditions, the Chinese water chestnut’s rhizomes grow horizontally and then turn upwards forming daughter plants. Under short-daylength conditions, the rhizomes grow downward and produce a corm at the tip, which is what you want if you’re growing this plant for the potato like corm.

It is these corms that we are after.  Once the corms turn dark brown, they are harvested.  If left in the soil after this point in time, the corms will get sweeter, however, shelf life will decline.  The corms can be harvested using a modified gladioli corm harvester once the paddy is drained.  Alternatively, a “water-suction harvester” can be used without the need to drain the paddy.   The corms have to be washed after harvest and brushed once they are dry.

Rich in carbohydrates (about 90% by dry weight), especially starch (about 60% by dry weight) the Chinese water chestnut is much like an aquatic potato, although cooked and used nothing like a potato.

 

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