The oca or oka is a perennial plant grown in the central and southern Andes for its starchy edible tuber, used as a root vegetable. Introduced to New Zealand as early as 1860, it has become popular in that country under the name New Zealand yam and is now a common table vegetable.
The oca is one of the important staple crops of the Andean highlands, second only to the potato.
The flavor is slightly tangy, and texture ranges from crunchy (like a carrot) when undercooked, to starchy or mealy when fully cooked. Though the original Andean varieties are widely variable in color from purple to yellow, the standard NZ variety is a fleshy pink.
Ocas need a long growing season, and are day length dependent, forming tubers when the day length shortens in the fall. In areas with harsh winter climates, the cold weather that accompanies shorter days may kill the plant before tubers have a chance to form. Likewise in tropical areas where the days are uniformly longer, the oca will not set a crop successfully, since the days are never short enough.
Ocas are fairly high in oxalates, concentrated in the skin, and traditional Andean preparation methods were geared towards reducing the oxalate level of the harvested vegetable. Recent oca cultivars have a lower oxalate content, and have also been selected for more flexibility in day lengths.
Oca potatoes are also known under the name of oxalis tuberosa plant. These potatoes have been the staple aliment in historical times, especially in the Andean culture, in the pre-Columbian times. Back then, oca potato served for making the traditional breads. Oca potato has a firm texture and it is medium in size – this is why it can be used for numerous recipes. Oca plantations produce 35 to 55 tons of tubers per hectare and some single plants can get to 4 kilograms. Oca is grown even at really high altitudes, until 4000 meters, as it is more resistant in cold conditions than other species of potatoes. The most impotent problem that affects the oca plantations is the oca weevil, which can destroy entire plantations in short amounts of time.
There are many ways to prepare oca potato: boiling, steaming, stewing or frying. Oca potato is mainly included in salads, which are served as garnishes and as main meals, or it is served fried in round and thick pieces or oven baked and topped with spices.