Purple-fleshed sweet potatoes are cool. The color is unlike any other food I’ve seen – yes, there are other purple foods, but none quite so thoroughly purple. I’m talking nasty bruise, Grimace from McDonald’s, Deep Russian amethyst purple. There is no confusing it for, say, maroon. They are so purple they almost look otherworldly, often eliciting oohs and ahs even from fairly jaded diners. But they don’t just look cool. They taste nice as well. Compared to their orange and white cousins, I think they taste a little richer and more fruity; I can always smell grape juice when I slice into them (although this aroma seems to disappear on cooking). In east Asia, they’re usually used in desserts, which makes a lot of sense; their flavor is more fruit than vegetable, but their texture is rich and dense, like ganache.
They’re also delicious in savory dishes, prepared any way you’d prepare ordinary sweet potatoes. But they weren’t so delicious in the dinner I made tonight, although that’s not the potatoes’ fault. I simply got it wrong in a number of ways.
It was a simple soup, flavored with various spices and topped with corn and a few other things for texture and contrast. First I sauteed some onion in a bit of butter until beginning to caramelise. I added fenugreek, garam masala, and Malaysian curry powder and let it roast among the buttery onions for a few minutes. I deglazed the pan with chicken stock and added diced purple sweet potatoes, which I brought to a low boil and cooked until completely soft. I pureed this mix with the stick blender until velvety smooth. I tasted it, and it was a bit lifeless, so I perked it up with sea salt and fresh bergamot juice.
(The bergamot juice actually brightened the color of the soup slightly; the pigment that makes purple sweet potatoes purple is pH-sensitive and will change drastically depending on how acidic or alkaline it is. If you were to add a basic ingredient to this soup, like baking soda, it would turn blue. If you added lots of it, it would even turn green. In the other direction, adding lots of bergamot juice would have made my soup turn yellow-ish orange. Science!)
I dished up the puree and topped it with corn and a tangle of spring onions, coriander, and finely julienned ginger. A light drizzle of chilli oil and it was good to go. Or so I thought. It wasn’t a total disaster, but there was an awful lot wrong with the dish. The soup was far too thick – more of a puree – which made the whole thing far too heavy, almost like pudding. The garam masala was overpowering, which gave the dish an underlying muddiness. And the spring onions were too crunchy and tough, add odds with what was otherwise a very soft, smooth dish.
However, it still has promise. The combination of the corn, fresh ginger, chilli oil, and puree actually made for a lovely mouthful. It just needs to be fine-tuned, and the spring onions certainly need to be left off. I have some leftovers, so I may return to this tomorrow to see if I can make it work.