|A bundle of cultivated asparagus|
Asparagus officinalis is a spring vegetable, a flowering perennial plant species in the genus Asparagus. It was once classified in the lily family, like its Allium cousins, onions and garlic, but the Liliaceae have been split and the onion-like plants are now in the family Amaryllidaceae and asparagus in the Asparagaceae. Asparagus officinalis is native to most of Europe, northern Africa and western Asia, and is widely cultivated as a vegetable crop.
Plants native to the western coasts of Europe (from northern Spain north to Ireland, Great Britain, and northwest Germany) are treated as Asparagus officinalis subsp. prostratus (Dumort.) Corb., distinguished by its low-growing, often prostrate stems growing to only 30–70 cm (12–28 in) high, and shorter cladodes 2–18 mm (0.079–0.709 in) long. It is treated as a distinct species, Asparagus prostratus Dumort, by some authors.
Asparagus has been used as a vegetable and medicine, owing to its delicate flavour, diuretic properties, and more. It is pictured as an offering on an Egyptian frieze dating to 3000 BC. In ancient times, it was also known in Syria and in Spain. Greeks and Romans ate it fresh when in season, and dried the vegetable for use in winter; Romans even froze it high in the Alps, for the Feast of Epicurus. Emperor Augustus created the “Asparagus Fleet” for hauling the vegetable, and coined the expression “faster than cooking asparagus” for quick action.[Note 1] A recipe for cooking asparagus is in the oldest surviving book of recipes, Apicius’s third-century AD De re coquinaria, Book III.
The ancient Greek physician Galen (prominent among the Romans) mentioned asparagus as a beneficial herb during the second century AD, but after the Roman empire ended, asparagus drew little medieval attention.[Note 2] until al-Nafzawi‘s The Perfumed Garden. That piece of writing celebrates its (scientifically unconfirmed) aphrodisiacal power, a supposed virtue that the Indian Ananga Ranga attributes to “special phosphorus elements” that also counteract fatigue. By 1469, asparagus was cultivated in French monasteries. Asparagus appears to have been hardly noticed in England until 1538,[Note 2] and in Germany until 1542.
The finest texture and the strongest and yet most delicate taste is in the tips. The points d’amour (“love tips”) were served as a delicacy to Madame de Pompadour. Asparagus became available to the New World around 1850, in the United States.
|Nutritional value per 100 g (3.5 oz)|
|Energy||85 kJ (20 kcal)|
|Dietary fibre||2.1 g|
|Vitamin A equiv.||
|Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database
Only young asparagus shoots are commonly eaten: once the buds start to open (“ferning out”), the shoots quickly turn woody.
Water makes up 93% of Asparagus’s composition. Asparagus is low in calories and is very low in sodium. It is a good source of vitamin B6, calcium, magnesium and zinc, and a very good source of dietary fibre, protein, beta-carotene, vitamin C, vitamin E, vitamin K, thiamin, riboflavin, rutin, niacin, folic acid, iron, phosphorus, potassium, copper, manganese and selenium, as well as chromium, a trace mineral that enhances the ability of insulin to transport glucose from the bloodstream into cells. The amino acid asparagine gets its name from asparagus, as the asparagus plant is relatively rich in this compound.
The shoots are prepared and served in a number of ways around the world, typically as an appetizer or vegetable side dish. In Asian-style cooking, asparagus is often stir-fried. Cantonese restaurants in the United States often serve asparagus stir-fried with chicken, shrimp, or beef. Asparagus may also be quickly grilled over charcoal or hardwood embers. It is also used as an ingredient in some stews and soups. In recent years asparagus eaten raw, as a component of a salad, has regained popularity.
Asparagus can also be pickled and stored for several years. Some brands label shoots prepared this way as “marinated”.
Stem thickness indicates the age of the plant, with the thicker stems coming from older plants. Older, thicker stalks can be woody, although peeling the skin at the base removes the tough layer. Peeled asparagus will however poach much faster. The bottom portion of asparagus often contains sand and dirt, so thorough cleaning is generally advised before cooking.
Green asparagus is eaten worldwide, though the availability of imports throughout the year has made it less of a delicacy than it once was. In Europe, however, the “asparagus season is a highlight of the foodie calendar”; in the UK this traditionally begins on 23 April and ends on Midsummer Day. As in continental Europe, due to the short growing season and demand for local produce, asparagus commands a premium price.
White asparagus in continental northwestern Europe
Asparagus is very popular in the Netherlands, Spain, France, Poland, Belgium, Germany, Austria, Italy and Switzerland, and is almost exclusively white; if not, it is specified by the local language term for “green asparagus”. White asparagus is the result of applying a blanching technique while the asparagus shoots are growing. Compared to green asparagus, the locally cultivated so-called “white gold” or “edible ivory” asparagus, also referred to as “the royal vegetable”, is less bitter and much more tender. Freshness is very important, and the lower ends of white asparagus must be peeled before cooking or raw consumption.
Only seasonally on the menu, asparagus dishes are advertised outside many restaurants, usually from late April to June. For the French style, asparagus is often boiled or steamed and served with hollandaise sauce, melted butter or olive oil, Parmesan cheese or mayonnaise. Tall, narrow asparagus cooking pots allow the shoots to be steamed gently, their tips staying out of the water.
During the German Spargelsaison or Spargelzeit (“asparagus season” or “asparagus time”), the asparagus season that traditionally finishes on 24 June, roadside stands and open-air markets sell about half of the country’s white asparagus consumption.
Effects on urine
The effect of eating asparagus on urine has long been observed:
- “[Asparagus] cause a powerful and disagreeable smell in the urine, as every Body knows.” (Treatise of All Sorts of Foods, Louis Lemery, 1702)
- “asparagus… affects the urine with a foetid smell (especially if cut when they are white) and therefore have been suspected by some physicians as not friendly to the kidneys; when they are older, and begin to ramify, they lose this quality; but then they are not so agreeable.” (“An Essay Concerning the Nature of Aliments,” John Arbuthnot, 1735)
- “A few Stems of Asparagus eaten, shall give our Urine a disagreable Odour…” (“Letter to the Royal Academy of Brussels,” Benjamin Franklin, c. 1781)
There is debate about whether all—or only some—people produce the smell, and whether all (or only some) people identify the smell. It was originally thought this was because some of the population digested asparagus differently from others, so some people excreted odorous urine after eating asparagus, and others did not. In the 1980s three studies from France, China and Israel published results showing that producing odorous urine from asparagus was a common human characteristic. The Israeli study found that from their 307 subjects all of those who could smell ‘asparagus urine’ could detect it in the urine of anyone who had eaten asparagus, even if the person who produced it could not detect it. However, a 2010 study found variations in both production of odorous urine and the ability to detect the odour, but that these were not tightly related. It is believed most people produce the odorous compounds after eating asparagus, but only about 22% of the population have the autosomal genes required to smell them.
In 2010, the company 23andMe published a genome-wide association study on whether participants have “ever noticed a peculiar odor when you pee after eating asparagus?” This study pinpointed a single-nucleotide polymorphism (SNP) in a cluster of olfactory genes associated with the ability to detect the odor. While this SNP did not explain all of the difference in detection between people, it provides support for the theory that there are genetic differences in olfactory receptors that lead people to be unable to smell these odorous compounds.
Certain compounds in asparagus are metabolized to yield ammonia and various sulfur-containing degradation products, including various thiols and thioesters, which give urine a characteristic smell.
- dimethyl sulfide
- dimethyl disulfide
- dimethyl sulfoxide
- dimethyl sulfone
Subjectively, the first two are the most pungent, while the last two (sulfur-oxidized) give a sweet aroma. A mixture of these compounds form a “reconstituted asparagus urine” odor. This was first investigated in 1891 by Marceli Nencki, who attributed the smell to methanethiol. These compounds originate in the asparagus as asparagusic acid and its derivatives, as these are the only sulfur-containing compounds unique to asparagus. As these are more present in young asparagus, this accords with the observation that the smell is more pronounced after eating young asparagus. The biological mechanism for the production of these compounds is less clear.