Stevia is a short-lived perennial herb which has leaves that are used as a natural sweetener. It originates in South America, in moist hilly areas in eastern Paraguay but nowadays is widely cultivated in many countries around the world, including Brazil, Taiwan, India and the United States.
A small shrub with a bushy appearance, it is reaches 80 cm (2.6 ft) tall and consists of semi-woody stems on which grow opposite pairs of short-stalked, green elongated oval leaves that are toothed above the middle.
The flowers are small, five-petaled, white and are induced into bloom by short-day length from autumn to winter. They are followed by small tufted seed designed for wind dispersal.
There are many varieties as a result of selective breeding, with variation in plant height, overall appearance, leaf shape and size, as well as sweetness.
The leaves have been used as a sweetener for hundreds of years in native areas to sweeten teas and medicines. More recently, Stevia has gained popularity as a low-calorie sweetener and as a natural alternative to artificial sweeteners such as Saccharin.
The sweetness in the leaf comes from two main compounds, stevioside and rebaudioside, which when extracted and crystallised are many times sweeter than sugar by weight. The ratio of the two compounds in the leaf varies by variety and this determines the degree of liquorice or bitter aftertaste, with the least bitter and better tasting varieties having a high rebaudioside relative to stevioside content.
The extraction process in simple terms involves soaking the leaves in hot water to dissolve out the sweet compounds, then filtering the solution and evaporating it to produce a white powder or fine crystal.
Stevia is used commercially as a non-caloric sweetening agent, particularly in Japan, Brazil and Paraguay. In Japan, it is commonly used in confectionery, chewing gum, mints, non-alcoholic drinks, pickles, dried seafood, soy sauce and miso based products. It also has application in baked goods, due to its non-fermenting and non-browning properties and its high stability to heat and acid.
The leaves are also a rich source of chlorophyll, which is extracted from the leaves some plants for use in cosmetics, toiletries such as toothpaste, and as a natural green colouring agent, especially in foods that do not require heat treatment, such as chilled desserts. Chlorophyll is high in Vitamin K and for this reason is being widely promoted as a blood and liver tonic.
The wetted leaves in a leaf-bag placed over the eyes is reportedly effective in tightening the skin and smoothing out wrinkles.
Stevia is a non-caloric sweetener, making it suitable for use by diabetics and in weight-loss diets.
Short day lengths and lack of moisture induce flowering in Stevia, usually at the expense of leaf production. For this reason, subtropical and temperate areas with long summer days are better suited than tropical areas for cultivating Stevia, as are areas with adequate moisture during the growing period.
Grows naturally and is productive in moderately humid subtropical and tropical mid- to high-elevation climates, generally frost-free areas with annual lows of 12 to 20 °C, annual highs of 23 to 32 °C, annual rainfall of 1000 to 2000 mm and a dry season of 5 months or less.
Stevia can also be grown with irrigation in areas with low rainfall and a long dry season. It is in fact cultivated with irrigation in the Indian states of Gujarat and Punjab, in areas with annual rainfall all of less than 1000 mm and a dry season of up to 8 months.
New plants can be started from seed or cuttings but seedling plants do not come true to type, so cuttings are preferred. Cuttings are best taken from known varieties with desirable characteristics, such as a reduced tendency to flower and with a high rebaudioside to stevioside ratio.
Planting time is spring to early summer in subtropical areas and in tropical areas when there is sufficient soil moisture for establishment and growth. It is also well suited for growing in a container.
Performs best on rich, moist, free-draining loam and sand soils of a moderately acid to neutral nature, generally with a pH of 6.0 to 7.5 and on sites with full to partial sun exposure. It has poor tolerance to drought.
It is recorded as having naturalised in Japan, but there does not appear to be any record of it anywhere as a serious weed or invasive species.
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