How stevia extract is produced from stevia leaf

Stevia's path from field to food consists of several steps – from sowing and harvesting to agents and distributors. In the middle of the value chain are stevia refineries. They extract the sweet substances found in stevia's leaves and mixed them into stevia extract. In this article we will take a closer look at what stevia refineries do.

29 May 2020 •

The plant Stevia rebau­di­ana, often called just ste­via, has in its leaves sub­stances that are intense­ly sweet. These so-called ste­vi­ol gly­co­sides are extract­ed and can be used as sweet­en­ers in most foods and bev­er­ages. In this arti­cle we take a clos­er look at how ste­vi­ol gly­co­sides are extract­ed and concentrated.

Dried stevia leaves

Type of ste­vi­ol glycoside Proportion in dried ste­via leaves
Stevioside 5–10%
Rebaudioside A 2–5%
Rebaudioside C 1%
Dulcoside A 0,5%
Rebaudioside D 0,2%
Rebaudioside E 0,2%
Rebaudioside F 0,2%
Steviolbioside 0,1%
Rebaudioside M 0,1%

Stevia is grown in sub­trop­i­cal cli­mate around the world for its sweet leaves. It is the leaves that are har­vest­ed. Dried, they are thir­ty times sweet­er than reg­u­lar sugar.

The sweet­ness comes from sub­stances called ste­vi­ol gly­co­sides. They are named so because they con­sist of a ste­vi­ol moi­ety with sev­er­al glu­cose moi­eties bound to it.

The most com­mon ste­vi­ol gly­co­side is called ste­vio­side. They make up between five and ten per­cent of the dry weight of ste­via leaves. The next most com­mon is Rebaudioside A (often abbre­vi­at­ed Reb A), which rep­re­sents two to five per­cent of the ste­via leaves’ dry weight. Among those that are least are Rebaudioside M (or short­er Reb M).

Steviol gly­co­sides are extract­ed and refined at ste­viar refineries.

Extraction

The extrac­tion begins with the leaves being allowed to steep in hot water. Much like when you brew a cup of tea – though on a larg­er scale. After a time, the ste­via leaves are removed and the ‘tea’ is puri­fied in sev­er­al steps.

The puri­fied ‘tea’ then pass­es an ion exchange chro­mato­graph. It is a tube con­tain­ing a porous mate­r­i­al that cap­tures with elec­tri­cal charge the ste­vi­ol gly­co­sides of the decoc­tion and allows the rest to pass through. It can be likened to a sieve, where the sub­stance one want to get hold of can­not pass while the rest is flushed away.

Now, the cov­et­ed ste­vi­ol gly­co­sides are trapped in the sieve. To access them, the sieve is rinsed with pure alco­hol. Then the elec­tric charge releas­es the grip on the ste­vi­ol gly­co­sides and they are rinsed with the alcohol.

The next step will be to remove the alco­hol. Much can be sep­a­rat­ed by a mem­brane fil­ter, but the remain­ing alco­hol be removed by dis­til­la­tion. Unlike home-dis­till­ing, it is not the alco­hol we want, but what remains – a syrup sweet­ened by ste­vi­ol glycosides.

To remove the yel­low col­or cast of the syrup, it is passed through acti­vat­ed car­bon. Thereafter it is pressed to squeeze out a ste­vi­ol gly­co­side solu­tion which is fil­tered one last time to remove small resid­ual particles.

Finally, the ste­vi­ol gly­co­side solu­tion is then sprayed under high pres­sure into a tank filled with hot air. When the fine­ly divid­ed droplets meet the hot air, the very last of the flu­id evap­o­rates and crys­tals of ste­vi­ol gly­co­sides fall like snow.

Primary extract

The snow of ste­vi­ol gly­co­sides is called pri­ma­ry extract. It con­sists of all the var­i­ous ste­vi­ol gly­co­sides found nat­u­ral­ly in ste­via. How much there is of each depends on the raw mate­r­i­al – the dried ste­via leaves.

The leaves con­tain most­ly ste­vio­side, which has a rather bit­ter taste and a pal­pa­ble metal­lic after­taste. A much nicer fla­vor is offered by Reb A. And best in class is Reb M, which is does not at all have a bit­ter or metal­lic falvour, but tastes almost like sug­ar (except it is up to 350 times sweeter).

The amount of each of the ste­vi­ol gly­co­sides depends on a lot of things. There are, for exam­ple, refined ste­via that gives much more Reb A than oth­er vari­eties. And the amount of heat and sun deter­mines how much of the sweet sub­stances have been formed.

In oth­er words, the raw mate­r­i­al varies wide­ly, and with it varies the sweet­ness and taste of the pri­ma­ry extract. This makes it dif­fi­cult to use it in food pro­duc­tion, as the result would vary from batch to batch in that case.

What’s worse is that the 50 to 80 per­cent of the pri­ma­ry extract is ste­vio­side, which is not as enjoy­able as Reb A and Reb M.

For these rea­sons, the pri­ma­ry extract needs to be fur­ther refined before it reach­es you who devel­ops and pro­duces food or beverage.

Refining

In the last step, ste­vi­ol gly­co­sides are sep­a­rat­ed. This is done through repeat­ed recrystallization.

First, the ste­via extract is dis­solved in alco­hol. The solu­tion is heat­ed so that it evap­o­rates. The vapor is led into a tube or tow­er, called a dis­til­la­tion col­umn, to slow­ly cool down to a point where crys­tals begin to form.

The first time this occurs, it is main­ly crys­tals of ste­vio­side that are formed. These are fil­tered from the solu­tion and tak­en care of.

The rest of the solu­tion is heat­ed again and the vapour is once more led into the dis­til­la­tion col­umn. The sec­ond time, it is main­ly crys­tals of Reb A that are formed. These too are fil­tered from the solu­tion and tak­en care of.

The dis­til­la­tion can thus be repeat­ed a third time to obtain main­ly Reb C. A fourth time to obtain main­ly Dulcoside A. And so on.

The thus sep­a­rat­ed frac­tions of recrys­tal­lized ste­vi­ol gly­co­sides are not entire­ly pure from oth­er ste­vi­ol gly­co­sides. To ‘puri­fy’ the extracts from the oth­er ste­vi­ol gly­co­sides, each of the frac­tions is put through the same process again. They are dis­solved in spir­it, evap­o­rat­ed and recrys­tal­lized. Each time this is repeat­ed, the con­cen­tra­tion of the desired ste­vi­ol gly­co­side increas­es. In this way, one can reach a puri­ty (or rather a con­cen­tra­tion) that is clos­er to 99 percent.

The whole process is called refin­ing – which explains that plants that extract and puri­fy ste­vi­ol gly­co­sides are called refineries.

Mixing and packing

One may think that the pur­er the ste­via extract is, the bet­ter it is, but that is not always true. Therefore, the puri­fied ste­vi­ol gly­co­sides and the residue of oth­er ste­vi­ol gly­co­sides that always remains, are mixed to cre­ate ste­via extracts with vary­ing degrees of purity.

For Reb A, con­cen­tra­tions of 50, 60 and 80 per­cent are com­mon, in addi­tion to almost pure Reb A (95−99 per­cent). This means that a ste­via extract with 50 per­cent Reb A also con­tains almost 50 per­cent oth­er ste­vi­ol gly­co­sides (main­ly stevioside).

So why make the effort to puri­fy ste­via extracts if it is imme­di­ate­ly ‘unpu­ri­fied’? As sug­gest­ed ear­li­er, it gives an oppor­tu­ni­ty to cre­ate ste­via extract with a con­sis­tent qual­i­ty. If you buy such ste­via extract, you can trust that each batch tastes about the same as the pre­vi­ous one.

The thus pro­duced ste­via extracts, with vary­ing degrees of ‘puri­ty’, are pack­aged and then sold to agents, exporters and importers who in turn sell it to you or a dis­trib­u­tor. You can read all about it in the arti­cle: Stevia from the field to your prod­uct – then the val­ue chain looks like.

We import Reb A and Reb M to Europe

Do you know that we are an importer of Reb A and Reb M with 50 to 98 per­cent puri­ty? Our cus­tomers are larg­er food com­pa­nies and dis­trib­u­tors who resell to small­er food com­pa­nies. Do not hes­i­tate to con­tact us if you want to know where to buy our range of Reb A and Rev M.

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