Fall is the season for the tubers in the taro family, but the stalks of several taro are just coming to their midsummer peak. In Japan, these taro stalks are referred to as zuiki in general, and they feature prominently on the classic summer washoku menu.
There are many categories of roots and tubers eaten in Japan today, most of whose names incorporate some variation of the word imo. There are true potatoes and sweet potatoes — jaga-imo and Sastuma-imo. Then there are wild or native-but-cultivated tubers, including true yams, called broadly yama-imo. Finally, there are the taro relatives lumped under the sato-imo appellation. The “sato” in sato-imo means “village” or “hometown” and implies a cultivated crop of nonnative origin.
Sato-imo culture predates rice cultivation in Japan, arriving from India by way of Indonesia in the late Jomon Period. Most sato-imo are raised for the waxy tubers, which are occasionally grated and eaten raw or steamed; if not, they’re left whole and boiled then simmered slowly in a flavored stock. However, the stems of a few of these tubers are also eaten. A few members of the sato-imo family have, in fact, come to be cultivated just for the stalk.
Like green zuiki, which is usually called hasu-imo. Hasu is another word for renkon (lotus root), and the stalk of this plant is so called because when cut across the grain, the gossamer holes look like a miniature version of crosscut lotus root. Hasu-imo must be peeled and is often soaked in cold water — to leach out any bitterness — before eating, but it is the only taro stalk that can be eaten raw. It is often used as a garnish for sashimi but is also very nice in any salad or even fried as tempura. Fukushima and Kochi prefectures are major producers of hasu-imo.
Red zuiki, or beni-zuiki, is the stalk of the touno-imo, grown and eaten mostly in and around Osaka and the southern Kawachi region. Beni-zuiki is unbearably bitter when raw (and slightly toxic) but delicious after it has been cooked and seasoned. It also contains a high level of calcium and potassium, which prompted early midwives to prescribe beni-zuiki to postpartum mothers. Called Higo-zuiki when dried, for the old kingdom of Higo (present-day Kumamoto), several varieties of zuiki may be sun-dried and preserved to use all year-round.
The Yamatsu mizu-imo, named for the region in Saga Prefecture, is a local variety of taro stem that has become well-known throughout Japan. Exported to major domestic cities and sold in the local markets from midsummer through fall, Yamatsu mizu-imo is often confused with the stem of the native wild yam yatsugashira. However, it may be treated similarly (and also must always be cooked).
In Japanese cooking, there are several words for bitterness. Akuis the general word for the bitter properties in some food ingredients, but it may also mean the scum that forms on the top of a simmering stock. Nigai is the adjective for general bitterness, but it has somewhat neutral connotations. Egui, or egumi, is a much harsher word that defines undesirable acrid properties.
Interestingly, humans have evolved a way to avoid consuming plants that are extremely bitter. When we eat such a plant, our innate gag reflex kicks in and prevents us from swallowing. It must be a survival mechanism, since many bitter plants are toxic.
This is true with the stalks of several taro. If you try to eat a small piece of beni-zuiki raw, your throat will constrict. However, once the bitterness — as well as the toxicity — is removed, then the summer vegetable becomes very palatable.
Beni-zuiki no usukuchi-daki
This is a simple simmered dish of beni-zuiki taro stalk. First, it must be peeled by taking hold of the skin at either end of the stem; it should come off in several swift pulls.
The peeled zuiki should be placed in vinegared (acidulated) water to prevent discoloration and to begin drawing out the bitterness. Older cookbooks actually recommend wearing gloves or covering your hands with salt to prevent your skin from turning black when peeling the zuiki, but I have found that modern cultivated zuiki is not as bitter as that.
Before seasoning zuiki, it should be blanched in boiling acidulated water, drained and cooled. Zuiki is nice served cold.
1 stalk (about 200 grams) beni-zuiki
vinegar and water to blanch
For the simmering stock
3 tablespoons vinegar
2 tablespoons dashi
1 tablespoon usukuchi shoyu (light soy sauce)
1) Peel zuiki, cut into 3-4 cm lengths and soak in vinegared water until blanching.
2) Boil vinegared water in a medium stockpot, add zuiki and cook for three minutes, then strain and cool with a fan.
3) In a smaller pan, add 3 tablespoons vinegar, 2 tablespoons dashi and 1 tablespoon shoyu and bring to a quick boil. Add blanched zuiki and continue cooking for another three minutes. Remove from heat; cool.
4) Serve at room temperature, or well chilled, garnish with ground sesame if desired.