Types of Asparagus
Green asparagus derives its colour from the process of photosynthesis as the spear emerges from the soil into direct sunlight. A common misconception is that thin spears are young shoots and therefore more tender. In fact, long, thick dark green glossy spears with tightly closed heads are the best quality. Correct cooking results in vibrant green spears with a delightful tender crisp texture. Green asparagus is usually available from the Koo Wee Rup area of Victoria from early September until the end of March. See also Preparing & Cooking Green Asparagus.
White asparagus has long been considered a delicacy, particularly by Europeans, and commands about double the price of green asparagus. White asparagus is exactly the same variety as green asparagus grown in Australia. The difference is that white asparagus is grown in the dark. When asparagus spears are exposed to sunlight, they first turn pink and later, the familiar green colour.
The main reason that white asparagus is more expensive is that there is a limited supply, and the production costs are high. Traditionally white asparagus was produced in the field by hilling up extra soil above the crown so that the spear could develop to a harvestable length without being exposed to sunlight. As soon as the spear emerged from the mound, specialist and skilled workers would cut deep into the mound with their purpose built long handled asparagus to harvest it. This method was not without its problems, as “blind harvesting” increased the risk of injuring the developing spears, and few specialist cutters were available to harvest the crop.
The increasing demand for new types of asparagus has led to developments in the way that white asparagus is produced. Some growers now use black “polyhouses” or “igloos” constructed over the crop between June and July in preparation for the emerging crop. The black plastic ensures that the spears are not exposed to sunlight. It also solves the problem of the traditional harvesting methods as asparagus grown in “polyhouses” can be harvested above the ground cleanly and efficiently without damaging the developing spears.
At the end of the season, the “polyhouses” are removed to allow the crop to continue its life cycle and produce the normal asparagus fern. White asparagus is usually available from September to January. See also Preparing & Cooking White Asparagus.
Thanks to Dr Peter G Falloon, Managing Director of Aspara Pacific Ltd in New Zealand for the following information about Purple Asparagus. Purple asparagus is a different variety to green and white asparagus. Its purple colour comes from the high levels of anthocyanins (potent antioxidants) in the spears. It has a lower fibre content than white or green asparagus, making it more tender and the whole spear can be eaten from tip to butt. Purple asparagus produces sweeter, thicker spears than green or white asparagus. Fresh purple asparagus is deeply fruit flavoured and tender crisp. It is usually available in Australia between mid October and mid November but currently only in limited supplies. See also Preparing & Cooking Purple Asparagus.