Celeriac (Apium graveolens rapaceum) is also known as celery root, turnip-rooted celery or knob celery. It is a kind of celery, grown as a root vegetable for its large and bulbous hypocotyl rather than for its stem and leaves. The swollen hypocotyl is typically used when it is about 10–12 cm in diameter; about the size of a large potato. Unlike other root vegetables, which store a large amount of starch, celery root is only about 5-6% starch by weight.
Celeriac may be used raw or cooked. It has a tough, furrowed, outer surface which is usually sliced off before use because it is too rough to peel. Celeriac has a celery flavour, and is often used as a flavouring in soups and stews; it can also be used on its own, usually mashed, or used in casseroles, gratins and baked dishes. It can be roasted like a potato, giving it a crispy edge.
The hollow stalk of the upper plant is sometimes cut into drinking straw lengths, rinsed, and used in the serving of tomato-based drinks such as the Bloody Mary cocktail. The tomato juice is lightly flavoured with celery as it passes through the stalk.
Celeriac is not as widely used as some other root vegetables, perhaps because it is harder to prepare and clean. Like other root vegetables celeriac is pretty good at taking on the flavors of the dishes in which it is used as an ingredient. For example it can be hard to discern from a potato or a parsnip in a dish such as osso bucco.