Oca is a tuber crop native to the Andes mountains of South America, where it ranks as the second most important root vegetable after the potato. It produces small, colorful, finger-shaped tubers with a waxy skin and a flavor that ranges from tangy and lemony to remarkably sweet, depending on the variety and how it’s prepared. If you’ve seen it labeled “New Zealand yam” at a market, that’s the same plant.
A Tuber From the Andes
Oca belongs to the wood sorrel family, the same group as the clover-like plants you might recognize from gardens and sidewalk cracks. Its scientific name is Oxalis tuberosa, and genetic research traces its wild relatives to Bolivia. Andean farmers have cultivated it for centuries at high altitudes where potatoes also thrive, valuing it for reliable yields and versatility in the kitchen.
The plant grows as a bushy, low-spreading crop with clover-shaped leaves. Underground, it forms clusters of small tubers, typically 5 to 15 centimeters long, with a knobby, wrinkled surface. Those tubers come in a striking range of colors: yellow, orange, red, pink, purple, and even near-white. The flesh inside can differ from the skin color, and purple varieties in particular are packed with plant pigments that act as antioxidants.
What Oca Tastes Like
Freshly dug oca has a distinctly tart, citrusy bite. That acidity comes from oxalic acid, the same compound found in spinach and rhubarb. Some people enjoy the tanginess raw, but traditional Andean practice is to leave harvested tubers in the sun for several days. Sun exposure breaks down the acid and converts starches into sugars, dramatically sweetening the tubers. Some varieties become so sweet after sun-curing that they’re eaten as a fruit rather than a vegetable.
The texture after cooking falls somewhere between a waxy potato and a carrot: firm but creamy, with a slight crunch if roasted at high heat. The flavor profile shifts with preparation. Roasted oca caramelizes beautifully. Boiled, it becomes mild and starchy. Raw, it stays crisp and tangy, almost like a tart apple.
Nutrition at a Glance
Fresh oca is about 80% water, putting it in the same ballpark as potatoes. The carbohydrate content runs between 10% and 14% by weight, with roughly 10.6% as starch and the rest as sugars. Protein is low at around 1.1%, and fiber sits at about 0.8% per 100 grams of fresh tuber. When dried, oca becomes a concentrated energy source, delivering around 370 calories per 100 grams.
Where oca really stands out is vitamin C. Fresh tubers contain approximately 187 milligrams per 100 grams, which is more than three times the amount in an orange. That made it a critical source of this vitamin for Andean communities living at elevations where citrus fruit doesn’t grow. The tubers also contain phenolic compounds, including caffeic acid derivatives and flavonoids, which contribute antioxidant activity. Purple-skinned varieties are especially rich in these compounds, with pigments from the same family found in blueberries and red wine grapes.
Oxalic Acid: Worth Knowing About
Fresh oca contains about 135 milligrams of oxalic acid per 100 grams. For context, raw spinach contains roughly 600 to 750 milligrams per 100 grams, so oca is considerably lower. Still, oxalic acid can bind to calcium and contribute to kidney stones in people who are susceptible. Cooking reduces oxalic acid levels, and the traditional sun-curing method lowers it further while also improving flavor. If you’re prone to kidney stones, treating oca the way you’d treat spinach or beet greens is sensible: enjoy it in normal amounts, and cook it rather than eating large quantities raw.
How to Cook With Oca
Oca works anywhere you’d use a potato or sweet potato, with the added option of eating it raw. In Mexico, raw oca is served sliced with salt, lime juice, and chili pepper, almost like a crunchy salad ingredient. In the Andes, it goes into stews and soups, gets boiled alongside other root vegetables, or is prepared as a sweet dish cooked down with milk and sugar.
Roasting is one of the simplest and most popular preparations outside South America. Toss whole or halved tubers in oil with salt and pepper, spread them on a baking tray, and roast at 200°C (about 400°F) for around 20 minutes, turning once halfway through. They’re done when a fork slides in easily. The edges caramelize and the interior turns soft and slightly sweet. You can also steam, boil, or deep-fry them.
A traditional Andean preparation called kawi (sometimes spelled cawi) involves cutting tubers lengthwise into quarters and drying them slowly in the sun over one to four weeks, turning them daily. The result is a chewy, deeply sweet dried tuber used to make desserts. Another classic dish, mazamorra de ocas, simmers fresh tubers in milk with sugar until they break down into a warm, porridge-like sweet.
Growing Oca Outside the Andes
Oca’s biggest quirk as a garden crop is its tuber timing. Most varieties only begin forming tubers when daylight drops below 12 hours, which happens after the autumn equinox in late September. That means the plant spends the entire spring and summer growing foliage without producing anything underground. Tubers then develop over the following six weeks or so, putting the earliest realistic harvest in early November for growers in the Northern Hemisphere.
The challenge is keeping plants alive long enough. Oca is frost-tender, so a hard freeze in October can kill the foliage before tubers have had time to bulk up. Growers in mild or coastal climates have the best luck, and many aim for a harvest between late November and early December. Waiting until December can yield close to the plant’s full potential, but gains taper off after the first of the month. In climates with early frosts, row covers or cold frames can buy the extra weeks needed.
New Zealand has become the most successful commercial grower of oca outside South America. Farmers there developed varieties suited to temperate conditions, and the tubers are sold simply as “yams” in New Zealand supermarkets. Some of those New Zealand-bred varieties also perform well in parts of Europe and the Pacific Northwest of North America, where mild autumns allow the long growing season oca demands.
Varieties and What to Look For
There is no single “oca” flavor or appearance. Andean farmers maintain dozens of named varieties, and New Zealand breeders have added more. Colors range from pale lemon yellow to deep crimson and purple, and flavor varies just as widely. Yellow and orange types tend to be milder and starchier. Red and purple varieties often have a more pronounced tartness when fresh, along with higher concentrations of antioxidant pigments. Some varieties are bred specifically for sweetness and can be eaten raw after a few days of sun exposure with no sour bite at all.
When buying oca, look for firm tubers without soft spots or sprouting. They store well in a cool, dark place for several weeks, similar to potatoes. If you want to reduce the tartness, leave them in a sunny spot for two to five days before cooking. The skin is edible and doesn’t need peeling, which preserves much of the vitamin C and pigment content concentrated just beneath the surface.