As I mentioned in Extract Sweeteners, pretty much any version of stevia that you can buy is an extract. You can buy dried stevia leaves, but having never done that myself, I cannot personally vouch for their quality or process. However, I have tried it, and in its natural form the stevia leaf has a strong, liquoricey, grassy taste; and, as a lot of you might recognise, it has a definite bitter aftertaste.
Almost all commercially-available ‘stevia’ is actually a steviol glycoside called Rebaudioside A, which is a compound that makes up part of the chemical structure of stevia. There are a lot of products that use Rebaudioside A as a basis, including Natvia and Truvia, and because its natural sweetness is so much higher they tend to use a teeny tiny amount (often 1% or less by weight) of Rebaudioside A and bulk it out with maltodextrin (which is a fructose-free polysaccharide (a sugar)) or a sugar alcohol like erythritol or xylitol.
Having done some experimentation, I’ve found that the actual purity vs. quantity of the Rebaudioside A extract has a big effect on the aftertaste (at least, from my personal experience). I’m currently using a product called Simply Wholesome Stevia Extract Crystals. It’s just about the purest Rebaudioside A extract available (around 98.7%), and it isn’t bulked out. I don’t find it to have nearly the same kind of bitter aftertaste, but because it is ‘pure’ (i.e. only stevia extract with no bulking agent), it is incredibly sweet; I have problems trying to measure it out, because you need about 1/30th of a teaspoon to get the same sweetness as table sugar. On the plus side, I purchased 100g of it 6 months ago and still have three-quarters of it left.
However, for those that have been eternally put off by that bitter kick, I recently discovered that scientists have managed to ‘decouple’ the bitter triggers in Rebaudioside A. However, they have done this by binding it to bovine serum albumin, so I’m not sure if that technically makes it non-vegetarian? But regardless, it’s a very interesting development. Feel free to figure out what ‘interesting’ means in this context.
In its natural form, stevia is a leaf that grows in South America. The most common sweetener extract from the stevia leaf is Rebaudioside A, which is a steviol glycoside, and the one with the highest sweetness and lowest bitter aftertaste of other glycosides. Although steviol glycosides do comprise at least two glucose chains (Rebaudioside A actually has 3), they are not a reducing sugar, and so will not melt or brown in a Maillard reaction.
The raw stevia leaf has an earthy, grassy, liquorice taste with a bitter aftertaste, but can be up to 30 times as sweet as sugar. Commercial products like Natvia & Truvia tend to use another bulking agent (maltodextrin, erythritol or dextrose, commonly) to make their sweetener spoon-for-spoon the same sweetness, and attempt to mask the naturally-occurring bitter aftertaste which comes with all stevia extracts.
What I have personally found is that products like Truvia and Natvia still tend to have that bitter, chemical aftertaste just like the ‘pure’ versions of stevia. To be fair, that tends to be true for pretty much any stevia-based sweetener because Rebaudioside A triggers both sweet AND bitter taste receptors (specifically receptors hTAS2R4 & hTAS2R14). However, some people seem to be more receptive to this effect than others, so they don’t seem nearly as averse to the aftertaste (either that, or they’re kidding themselves). I have always been able to taste that bitterness, and as a result I almost never use stevia as a sweetener on its own.
|Sweetness Where table sugar has a sweetness of 100%||2400%||100%|
|Glycemic Index Where glucose has a G.I. of 100||0||65|
|Calories per teaspoon Where a teaspoon is, on average, 4g||0||16|
There are no known side effects to to consuming stevia, either in its raw leafy form or a steviol glycoside like Rebaudioside A. There have been double-blind clinical studies that suggest stevioside (another steviol glycoside) may help to reduce blood pressure, however these test were carried out using comparatively high doses.