Stevia Article Series

How Is the Stevia Plant Processed Commercially?

Wednesday, 15 August 2012

The steviol glycosides, used as a sweetener, are extracted from the dried leaves of the Stevia rebaudiana (Bertoni) Bertoni plant. Pre-extraction the dried plant material is produced in the same way that vegetable crops are i.e. warm air drying at approx. 70°C for up to three hours until the moisture content reaches 5-8%. This prevents decomposition of the steviosides and allows the resulting plant material to be stored for up to two years.

There are, worldwide, numerous patents concerning the stevia extraction process, with a significant number originating in Japan. All processes consist of two main phases: Phase I, the initial processing of the stevia leaf, yielding a steviol glycoside intermediate-grade extract; Phase II, secondary processing which produces a final high-grade stevia extract product.

The first phase of the manufacturing process is the more capital intensive of the two. It is common, therefore, for these two phases to be undertaken by separate manufacturers, with the phase I extract being purchased by producers of the phase II final marketable product e.g. Cargill (Truvia).

An example of a typical manufacturing process for a high-quality rebaudioside A product is:

Phase I: The raw stevia leaf is converted to an intermediate-grade extract by the following processes: (a) the leaves are dried, crushed and then extracted with water; (b) the extract (resin) is subsequently washed in a food-grade ethanol thereby releasing the steviol glycosides which are; (c) concentrated with an adsorption resin, such as a styrene-divinylbenzene-methylacrylate copolymer adsorbent or active carbon, the latter of which has also been found to recover high amounts of rebaudioside A. This concentration process culminates in drying to form a ‘primary extract’.

Phase II: This secondary processing of the intermediate-grade extract follows two processes: (a) The resultant primary extract from phase I is dissolved in water, alcohol (ethanol or methanol) or water + alcohol. There then follows further processing through filtration, centrifugation and crystallization; (b) The resultant crystals are rinsed using food-grade ethanol and finally vacuum-dried giving the high-grade Rebaudioside A product.

A number of producers market their stevia products as ‘alcohol-free’, this tends to signify that water has replaced the alcohol, chemicals and solvents during the manufacturing process.

New methods are continually being developed to refine the process of extracting steviol glycosides from the the Stevia rebaudiana Bertoni plant, both to increase yield and reduce costs. We will endeavour to keep our website updated with the latest industry developments.