Taste & ingredients

Reb A vs Reb M: why some stevia tastes bitter and some doesn't

Two sweeteners from the same leaf. One can leave a bitter, liquorice finish. The other tastes much closer to sugar. Here is why.

Rawstone Learn · general education, not medical advice

If you have ever mixed up a sugar-free drink and caught a bitter, slightly liquorice note at the back of the sip, you have probably met Reb A. It is the most common form of stevia, and it is the reason a lot of people think they do not like stevia at all. The good news is that stevia is not one single sweetener. Some of it tastes much more like sugar. Here is what is going on, in plain terms.

What is actually in a stevia leaf

Stevia comes from the leaves of a small South American plant, Stevia rebaudiana. The leaves hold a family of naturally sweet compounds called steviol glycosides. They are many times sweeter than sugar, so a tiny amount goes a long way, and they carry no sugar.

There are lots of steviol glycosides in the leaf, and they do not all taste the same. Each one is built on the same core, with a different number of sugar units hanging off it. Two of them matter for your drink: Reb A (rebaudioside A) and Reb M (rebaudioside M).

Reb A: common, cheap, and sometimes bitter

Reb A is one of the most plentiful sweet compounds in the leaf, which makes it the easiest and cheapest to extract in bulk. That is why it is the stevia you meet most often.

The catch is the aftertaste. At higher doses, many people pick up bitterness or a liquorice finish. Researchers at the Technical University of Munich worked out why (Hellfritsch and colleagues, Journal of Agricultural and Food Chemistry, 2012). They screened 25 human bitter-taste receptors and found that steviol glycosides switch on two of them, called hTAS2R4 and hTAS2R14. So the sweetener is hitting your sweet receptors and a couple of bitter ones at the same time. They also found that glycosides carrying more sugar units tended to taste sweeter and less bitter.

Reb M: the clean one

Reb M is a minor glycoside. The leaf holds only a tiny amount of it. But it has a cleaner, more sugar-like taste than Reb A, with far less of that bitter tail. A 2014 review in the journal Foods, titled "Development of next generation stevia sweetener: rebaudioside M" (Prakash and colleagues), describes its clean, sweet taste and how well it works in food and drinks.

To be straight with you, no high-intensity sweetener is perfectly neutral if you overdo it, Reb M included. That is why the dose matters as much as the grade. A light hand with Reb M is about as close to sugar as stevia gets.

Where Reb M comes from

Because the leaf holds so little Reb M, pulling it straight out of leaves would take an impractical amount of stevia. So most Reb M is made at scale another way. Producers take the more plentiful sweet compounds from the stevia leaf and convert them into Reb M using enzymes, or they make it by fermentation. The finished molecule is Reb M, the same compound the leaf makes in small amounts. Food Standards Australia New Zealand has assessed and approved several of these enzyme-conversion methods.

How to spot it on a label

This is where labels get unhelpful. In Australia, stevia sweeteners are listed as sweetener (960) or as steviol glycosides. That covers Reb A, Reb M and the rest alike, so the type usually is not named.

Two practical tips. First, brands that pay for Reb M tend to say so, because it costs more and they are proud of it. If a brand does not mention it, ask. Second, trust your tastebuds: a bitter finish that hangs around after you swallow usually points to Reb A.

What Rawstone uses

Rawstone is sweetened with Reb M only, listed on the pack as sweetener (960). There is 0g of sugar, and we keep the sweetness dialled down so it tastes smooth, not syrupy. That matters in a full-strength electrolyte powder. A serve carries 1000mg of sodium, plus potassium and magnesium, and salt has its own sharp edge. A clean sweetener keeps the finish smooth instead of stacking a bitter note on top. Rawstone is Australian-owned, and our first flavour is Mango Passionfruit. For the bigger picture on the sodium dose, see is 1000mg of sodium too much, and for label tips, how to read an electrolyte label.

This article is general education about ingredients and taste, not medical or dietary advice. Rawstone is a food supplement, not a medicine, and is not intended to diagnose, treat, cure or prevent any disease. If you have a condition that means you need to manage what you consume, talk to your doctor before using any electrolyte supplement.