Celery root is a cultivated form of wild celery (Apium graveolens var. Graveolens). Like the two other varieties of celery, green stalk celery and Chinese celery, celery root is used in dishes as a vegetable. Celery contains essential oils in its oil passages. The phthalides they contain are responsible for the typical flavor of celery.
Celery root has a round-shaped root, which can weigh as much as one kilogram. The leaves of the tuber resemble those of parsley and can be used to add flavor to food. The skin is yellowish-white to gray-brown and has a gnarled appearance. The pulp is white to beige.
From Wikipedia: “Celeriac (Apium graveolens var. rapaceum), also called turnip-rooted celery or knob celery, is a variety of celery cultivated for its edible roots, hypocotyl, and shoots. It is sometimes called celery root. ...
Celeriac is a root vegetable with a bulbous hypocotyl. In the Mediterranean Basin and in Northern Europe, celeriac grows wild and is widely cultivated. It is also cultivated in North Africa, Siberia, Southwest Asia, and North America. In North America, the Diamant cultivar predominates. Celeriac originated in the Mediterranean Basin.”
“At 19 kcal / 100 g, the tuber cell line has a low caloric content with a high content of vitamins and minerals. It has a high mineral content containing potassium, iron and calcium making it a valuable vegetable. Celery also contains carotenoids, vitamin C and B group vitamins.*”
“Typically, celeriac is harvested when its hypocotyl is 10–14 cm in diameter. However, a growing trend (specifically in Peruvian and South American cuisine) is to use the immature vegetable, valued for its intensity of flavour and tenderness overall. It is edible raw or cooked, and tastes similar to the stalks (the upper part of the stem) of common celery cultivars. Celeriac may be roasted, stewed, blanched, or mashed. Sliced celeriac occurs as an ingredient in soups, casseroles, and other savory dishes. The leaves and stems of the vegetable are quite flavoursome, and aesthetically delicate and vibrant, which has led to their use as a garnish in contemporary fine dining.”
Storage and freshness:
“The shelf life of celeriac is approximately six to eight months if stored between 0 °C (32 °F) and 5 °C (41 °F), and not allowed to dry out. However, the vegetable will tend to rot through the centre if the finer stems surrounding the base are left attached. The freshness of the vegetable can be determined by viewing the hollowness of the vegetable; a fresh celeriac should not have a hollow centre. The freshness of the vegetable will also be obvious from the taste; the older the vegetable, the less potent the celery flavor.”
“Celery can cause allergic reactions up to anaphylactic shock (celery-carrot-mugwort-spice syndrome).*”
Peeled celery root discolors very quickly. Drizzling some lemon juice on the raw celery root or adding vinegar or lemon juice to the cooking water will help to prevent this.
Note (italics): * = Translation from a German Wikipedia entry