A counterintuitive fact about stevia extract

Choosing the right stevia extract is like choosing clothes for a long journey. Which should you bring? There are different varieties to choose from, with different characteristics and degrees of sweetness. And there is no such thing as a pure stevia extract. All come with a mix of different steviol glycosides. Therefore, you must think through which stevia extract to choose, and how pure it must be.

Purity or concentration?

We have a linguistic problem when talking about stevia extract. We often talk about the ‘purity’ of a stevia extract, when we really mean the amount of a certain steviol glycoside in that extract.

Take, for example, our own Navia 60, which consists of 60 per cent of the steviol glycoside Reb A. Often, it is said to have 60 per cent purity. That doesn’t mean there is 40 per cent dirt, but rather 40 per cent of other steviol glycosides.

Perhaps ‘concentration’ is a more appropriate term. The purity of Reb A is always one hundred per cent independent of its concentration.

Therefore, let’s use concentration in this article.

The higher the better?

But why should we talk about concentration? Is it important?

One may think that the higher the concentration, the better. And by all means. Sometimes it may very well be the case – but not always.

We start from the beginning.

Glycoside bonds

The molecule of any steviol glycoside consists of several glucose moieties linked by glycoside bonds to a single steviol moiety, acting as a backbone. The number of glucose moieties determines its characteristics, e.g. its sweetness, bitterness, amount of liquorice off-taste and length of aftertaste.

Sweet, sweeter, sweetest

Some steviol glycosides are more pleasing than others. Reb A, with its great sweetness, will always be more popular than stevioside – its more bitter-tasting predecessor. And then we have Reb M, which has almost a sugarlike taste, thanks to six glucose moieties. But Reb M is not always preferable, strange as it may sound. It is not just the sweetness that matter when it comes to steviol glycosides. Its taste must also fit the desired flavour profile of a product.

So what to do, if you have a product with very particular taste requirements, and you want to sweeten it with steviol glycosides?

The solution is to use stevia extract with not too high concentration. That’s right!

High concentration isn’t always preferably

If you have read the article Masking off-taste – a balancing act, then you know that mixing steviol glycosides is one of many ways to mask unwanted off-taste. That’s why a stevia extract with a low concentration of Reb A (let’s say 50 or 60 per cent) can be better than one with high concentration (for instance 98 per cent).

In the dawn of refining steviol glycosides, this counterintuitive result emanated as an unexpected bonus of attempts to keep the cost down.

Genesis

Let’s go back to the time before steviol glycosides became approved in the EU.

Stevia plants from that time did not contain much Reb A. But there was an abundance of stevioside, which has a quite bitter and not so pleasant taste. So using stevia extract with natural proportions of steviol glycosides gave products a noticeable bitter and liquorice-like off-taste. Understandably, these products got a lukewarm reception.

Were steviol glycosides really the future?

A lower concentration

Fortunately, stevia plants have been cultivated to give more Reb A. But their leaves still contain most stevioside (5–10 %), followed by Reb A (2–4 %) and minor quantities of the other steviol glycosides (including the attractive Reb M, which constitutes less than 0.1 % of the dry weight of leaves). But now there was at least more of Reb A available, but its price tag was still quite hefty.

The solution to the problem, that Reb A is expensive and that stevioside is less flattering to the taste, became stevia extracts with a lower concentration of Reb A.

The surprising result

To everyone’s surprise, the stevia extract with less Reb A did taste quite well. In fact, many people thought applications with a lower concentration of Reb A tasted even better than applications with Reb A alone. It seemed that synergistic effects arose when the various steviol glycosides were allowed to meet.

And here we are today.

A real-life example

For many food and beverage producers, the goal isn’t to remove sugar altogether but reduce as much as possible without a negative effect on taste.

With that goal, a soft drink company reduced the added sugar in a lemon and lime drink with 50 per cent with a stevia extract with a high concentration of Reb A.

When they later replaced the stevia extract with another with a lower concentration of Reb A, they could reduce the added sugar even more – to only 25 per cent.

The yoghurt evaluation

Another proof of that stevia extract with lower concentration of Reb A can be better than a stevia extract with high concentration is found in a patent application as an interesting experiment with yoghurt.

The setup is simple.

We have samples of yoghurt numbered one through six. The first four has a small amount of added sugar, and the last two has no sugar added.

In the first sample, Reb A was used with a 97% concentration. Unsurprisingly, the test participants said that the yoghurt tasted bitter.

The second sample contained Reb A and Reb B. The participants reported it tasted better but not as good as it could taste; they clearly felt a lingering aftertaste.

The third sample contained Reb A, Reb B and Reb D. Now, both the bitterness and the aftertaste disappeared.

The fourth sample contained Reb B and Reb D, but not Reb A. The sweetness was still present, even though it came a little late. But the participants reported a sensation of a dry, puckering mouthfeel like that caused by the tannins in unripe fruits. A taste sensation called astringency.

The fifth sample contained the same amount of Reb A and Reb B as the third sample, but less of Reb D. In comparison, this reduced the acidity and the sweet aftertaste.

The sixth and last solution contained the same amount Reb A, Reb B and Reb D as the third sample, but also various flavour enhancers and the natural sweetener thaumatin. This was the best solution, according to the test panel.

The winning formula was perceived as round in taste and sweetness without an unpleasant lingering, had balanced acidity and very little bitter stiffness.

A helping hand

The yoghurt-test is a telling one. Not just in how to use steviol glycosides. It also says a lot about what it takes to succeed in sugar reduction. It’s not easy. But we happily help you, both with steviol glycosides and professional services. We also have readymade solutions. So don’t hesitate to contact us.