A Tart Little Tuber from the Andes

ocaA couple of weeks ago I noticed the motley assortment of pots in the middle of my greenhouse floor, dragged there for minimal protection from the winter cold and now adorned with the limp, frozen foliage of various tender plants. Wasn’t that drooping bush at the side of one pot the top of the oca, a South American wood sorrel? I should have checked sooner to see if the plant had produced any tubers. Kneeling on the ground, I started digging.

My oca plant was actually two, in a single pot. I’d gotten two little tubers last spring from Rose Marie Nichols McGee, whose Nichols Garden Nursery is one of few North American suppliers of oca. Because the plant is sensitive to day length, Rose Marie had explained, the tubers are produced in mid-October in our region—if the plant is protected from frost.

That posed a problem for me, since in recent years the first frost has hit my garden in early October. So I decided to plant the ocas in a big pot on the deck, where I’d be sure to keep an eye on them. Before moving the pot to the greenhouse about October 1, I poked my fingers around the roots and felt no swellings.

Now I pulled out a pile of tubers, some less than an inch long and the longest four inches, each looking like a cross between a pink-skinned potato and a fat grub. Washed and dried, they looked shiny, as if rubbed with oil.

What was this strange vegetable? Oca is Spanish for oqa, apilla, cuiba, or ibia—all of which are among the indigenous South American names for one of several tubers traditionally farmed in the Andes, where oca follows potatoes both in popularity among root vegetables and in the customary crop rotation. Botanists call this tuber Oxalis tuberosa; Mexicans call it papa extranjera; and New Zealanders, who grow and consume substantial quantities, call it yam. (It helps to know these other names when you’re searching for information about the oca, because in Spanish oca also means “goose.”)

Like the potato, the oca comes in many colors—pink, red, yellow, white, and even black.

Unlike the potato, the oca is generally palatable when raw. Different varieties, however, vary in their levels of oxalic acid, which can interfere with mineral absorption in the body and lead to kidney stones. So in South America ocas are often treated to reduce the oxalic acid level—by setting the tubers in the sun for several days, by boiling them, and, in the case of high-oxalate varieties, by first fermenting and then freeze-drying them.

This doesn’t mean ocas aren’t good for you. They are rich in carbohydrates; they have almost twice the vitamin C content of potatoes; and some varieties have ample carotene. They also contain a soluble protein called ocatin, which has antifungal and antibacterial properties.

I had to taste some of my ocas right away. They were crisp as an apple straight from the tree, not sweet, but pleasant. Some had a slight sorrel taste; others were quite tart. Inside, the flesh was light golden. I left the remaining ocas in a bowl in front of a window for several days, turning them occasionally, but, as usual in western Oregon winters, the sun never came out.

I figured I’d better cook the rest before I absentmindedly ate them all raw.

So, how to cook my ocas? Ecuadorians, I learned, preserve ocas in syrup and combine them with berries in jam. Columbians serve boiled ibias, as they call them, with tomato-and-onion salsa. They also cook them with eggs in something like a Spanish tortilla, make them into jam, puddings, and cakes, and, most often, use them for chicha, a beverage of grain or root vegetables fermented with cane syrup and water.

I’d harvested a measly 9 ounces of ocas, and I wanted to save some for planting, so I had only about 4 ounces to spare. The recipes I found sounded either impractical for such a small quantity or, with the cupboard still full of Christmas sweets, too sugary to have much appeal. So I decided to use my ocas as I do so many other small pickings from the garden: in a stir-fry. I made–

Stir-fried Tofu, Ham, Leeks, and Oca over Steamed Mizuna

Weight and drain a pound of tofu, unless it’s quite firm, for half an hour or so. Slice it into cubes. Slice two small leeks, or one large one, crosswise into pieces about 2 inches long, and slice the white part thinly lengthwise. Cut about ¼ pound ham into ½-inch cubes. Rinse about a pound of mizuna. Mince two cloves of garlic and two quarter-size slices of ginger. Cut ¼ pound oca into approximate ½-inch cubes. (Ocas don’t need peeling.)

In a wok, deep-fry the tofu in vegetable oil until it is golden brown. Drain the tofu on paper towels or a paper bag, and pour out all but a teaspoon or two of the oil. Stir-fry the leeks briefly; add the garlic and ginger; toss; and scoop the leeks into a bowl. Stir-fry the oca briefly, and then add about 2 tablespoons water or sake, reduce the heat, and cover the wok. Cook the oca until they are as tender as you like. Put them in the bowl with the leeks. Add more oil to the wok, if needed, and briefly stir-fry the ham. Add soy sauce, pepper jelly, and sake to the wok to make a sauce. Return the tofu to the wok, and toss it to coat it with the sauce. Add the leeks, and toss again. Add a little roasted sesame oil, toss once more, and empty the contents of the wok into a bowl.

Steam the mizuna in the wok just until the greens are wilted. Spread them in a serving bowl or on a platter, and put the reserved tofu, ham, and vegetables on top. Serve the dish with steamed rice.

oca stir-fry

The oca skins lost most of their color with cooking. Can you see the little barely-pink chunks hiding among the tofu and ham cubes?

The stir-fried oca tasted a lot like water chestnut, though less sweet. I cooked it until it was fork-tender, but Robert and I agreed we’d probably like it better cooked only briefly, so that it would stay crisp.

In case you’d like to grow oca yourself, you can order starts from Nichols, Annie’s Annuals, or Raintree Nursery. To be sure your harvest is bigger than mine was, read this article from Mother Earth News.