(Oxalis tuberosa – Family Oxalidaceae)
Oca, Irbia, cuiba, New Zealand yam
Oca (pronounced with the accent on the “o”) is a member of the wood sorrel family, and only one of several names used for this plant in South America.
The word is derived from the Quechua o’qa or okka and scarcely known outside the Andes, except in the highlands of Central Mexico where it is known by the misleading name of papa roja (red potato).
To muddy the proverbial waters even more, in New Zealand, where the plant has been cultivated for about thirty years, it is called a yam. This tuber is not related to the potato or the yam and was introduced to New Zealand in the 1860s by an English immigrant who collected it in Chile.
The plant entered the US about the same time; but, before that,it made its way to England from Peru in 1829.
At present, all fresh oca in the US comes from New Zealand and sold at outrageous prices, despite the irony of its being known as a “poor man’s food” in its homeland. Today, it is rarely found in European or American gardens, despite it once being grown as a potato substitute.
The oca differs from other members of the family in that it is grown mainly for its tubers although, its spinach-like leaves and young shoots may also be eaten as green vegetables.
When freshly dug, the tubers have a strong acidic taste which disappears if left out in the sun for a few days, during which time, they also become sweeter.
They are easy to prepare and surprisingly good, but they must be properly prepared before eating in order to remove the calcium oxalate crystals.
These tuberettes are crisp and moist, thinned-skinned, sour-sweet, starchy and waxy with a fruity-vegetable flavour, and quite unlike anything else. They range in a variety of eye-catching colours from yellow to pink, violet, red, and striped. There is even a greater variation in sugar, acid, shape, and size.
Oca is a perennial, common in the high-altitude Andes from Venezuela to northern Argentina, where it is second only to the potato in popularity.
At the northern end of Lake Titicaca, there are more than 150 steep terraces
dating from the time of the Incas and still used for cultivation.
Tubers form in the autumn when daylight is less than nine hours and mature after eight months.
Breeding has formed new varieties that have reduced levels of calcium oxalate crystals, but they should still be left for several days in the sun to become soft before eating.
In South America, they are dried for several weeks in the sun until floury and less acidic and becoming sweet-tasting, similar to dried figs. The acidity can be removed by boiling in several changes of water.
The flavour also improves after they have been frozen.
After proper preparation, oca can be eaten raw, roasted, boiled, candied like sweet potatoes.