Stevia Article Series

How Can I Grow and Process My Own Stevia?

Friday, 29 September 2012

The three main stages in the production of any stevia product are growing, harvesting and processing.

Growing Stevia (propagation by cuttings or from seed): By far the easiest method of propagation is to start from a cutting of the Stevia rebaudiana (Bertoni) Bertoni plant. The aim is to take a cutting approx. 10cm long from a parent plant, using a sharp knife, making a diagonal cut. Ensure all large leaves are removed and that the lower part of the stem is free from leaves and the upper part includes a minimum of two leaf buds. Bury the lower part in a potting compost, using root powder where possible.

A simpler, but potentially less successful method is propagation from a high quality seed. The germination of stevia seeds is the same as for tomato seeds, namely; planting approx. 3mm deep in a seed starter mix (usually containing vermiculite, peat moss and perlite), firm the soil to ensure good contact with the seed, preserve moisture with a ventilated cover and keep in a warm location out of direct sunlight. Once the seedlings start to appear - move into brighter light for ideally 15 hours per day to give a good growth of leaves in these early stages and to prevent flowering.

Seedlings grown from seed can be moved outside 10 weeks after seeding, seedlings from cuttings take 4 - 6 weeks to establish a root structure for outside planting. Depending on location stevia plants may need to be brought inside/sheltered if outside temperatures drop below 40°F. As is the case with tomato plants stevia benefits from having its tips pinched every 3 weeks for the first couple of months to aid side branching so giving a bushier plant.

Harvesting Stevia: Depending on the environment stevia plants can either be (a) harvested and replanted yearly (avg. min. temp. 10°F) (b) harvested yearly and fall dormant for the winter (avg. min. temp. 10°F to 30°F) or (c) have the tops harvested yearly with continual top-growth throughout winter (avg. min. temp. 30°F). To get the maximum amount of steviol glycosides from the plant harvesting must take place as soon as flowering begins and before the first frost.

Harvesting in the morning is advised, after the dew has evaporated. For growing method (a) above the plant can be cut at ground level, (b) cut 6 inches above ground level to allow for regrowth in subsequent years. For (a), (b) and (c) minor harvesting takes place a number of times throughout the year, cut off the top half of the plant and allow to regrow, continue as long as climate permits. Wash the cut plants in clean water and hang out to dry, usually for 1 to 2 days, depending on humidity. There are references to the fact that a drying time of less than 8 hours maximises the yield of steviol glycosides. Leaves should be able to be crushed between the fingers once ready.

Processing Stevia Leaves: The simplest way to process stevia leaves is to grind dried leaves, usually in a blender, into a powder. This powder can then be used directly to sweeten beverages or as a substitute in cooking, although it may not always be suitable for the latter as the quantity used is far less.

An alternative method is to extract the steviol glycosides in a liquid extract form using water or alcohol. The latter is preferred to maximise yield. Allow a combination of raw or fresh leaves and alcohol (ethanol (grain alcohol) is used commercially, but vodka is an acceptable substitute) to steep for 24 hours. The resultant liquid can then be filtered off and simmered over a low heat to remove the alcohol and reduce. The extract will be incredibly sweet so it may be preferable to dilute to taste.