Sweet leaf no good to me
At lunch in a restaurant near to Palmas de Ocoa, just north of Santiago in Chile, I was about to try the exotic sauce brought to the table, thinking it some local delicacy. Then, when our host popped a little into her coffee I decided it was unlikely to go well with my Pastel de Choclo, a rather heavy version of Shepherd's Pie but with cornmeal instead of potatoes.
Apparently the sauce was a sweetening agent (as Lynda, who photographed it, noticed) and it was only when I got back to Australia I discovered I had missed a phenomenon, that of the Sugar Leaf. At a local nursery in Kew, Lynda pointed out the source plant to me, here labelled Sugar Herb.
Timely then to find out more about this plant and whether I'm likely to see more of it in home gardens and on dinner tables. A review paper from three years ago, authored appropriately by four Chilean scientists, is helpful.
Stevia rebaudiana is a daisy (in the family Asteraceae). It grows naturally as a shrub in the north-east Paraguay and nearby Brazil and Argentina. It has been sweetening yerba mate for at least a few centuries so for me to discover it on my South American adventure makes sense. Well, except that it is widely cultivated in North America, Asia and Europe, and clearly at least to some extent in Australia.
The leaves of Sweet Leaf or Sugar Leaf, as it is so helpfully called, are sweet and sugary because they contain chemicals called glycosides. A glycoside consists of sugar molecules bound to other 'non-sugar' molecules. Steviols, the important glycosides in the Stevia leaf, are about 300 times sweeter than table sugar (e.g. from sugar cane in Australia). Which means, as you'll read all over the web, that you can consume less of it to get the same sugar hit and therefore get less obese. Or something like that. You'll also soon learn that it cures pretty much any ailment you might have at the moment.
There are 230 species of Stevia but only two have the sought after steviol: Stevia rebaudiana and Stevia phlebophylla. Stevia rebaudiana is the one fussed over the most and seems to be the species in my local nursery. As you can see above, it has soft leaves with toothed margins, not unlike some kind of mint.
The flowers are small and white, and not immediately obvious as a daisy head. It needs to be kept well watered and away from the cold, although it can tolerate, but not enjoy, temperatures down to freezing. (There are many cultivated forms so some may be more adapted to Melbourne conditions than others.)
The Chilean scientists conclude that Sweet Leaf is non-mutagenic, non-teratogenic (i.e. doesn't cause birth defects) and non-carcinogenic. They say it has been consumed by humans for centuries without apparent negative effects. All of which they suggest makes it a better sugar substitute, if you need one, to (so-called) artificial sugar substitutes.
Some people, I gather, simply drop a leaf in their herbal tea. Me? Well I don't drink herbal tea and I won't allow any sweeteners near my double ristretto with a dash of hot milk (accepting of course that the milk brings along its lactose).
If I did, I think I'd be a traditionalist and add a spoonful of Sacchrum (Sugar Cane) or Beta vulgaris (Sugar Beet). I understand they too have been used for centuries and are non-nasty. My recommendation, for what it's worth, is to have fewer brews but make sure each one tastes great.
Note: I forgot at the time of writing I'd already posted a little on this plant, back in 2011, when I was living in London.