sweet potato fries

I remember the first time that I ate sweet potato fries, just a couple of years ago, and the thought that crossed my mind was, 'oh my, how has it taken me this long to discover these? I have to make them.' So, we attempted to make them, but always found that they were rather floppy, and not beautifully crisp, as they had been in the restaurant where we had discovered them. We tried a good few more times, varying the length of time we cooked them for, and coating them with cornmeal to try and help crisp them up. But they just weren't quite right, to the point where my husband (who is an excellent cook) decided they weren't really worth the bother. 

That all changed on Sunday, after John had listened to a BBC podcast, with the Harold McGee, who is the man who inspired Heston Blumenthal and all of his adventures with chemistry and cooking. He explained the crucial difference between white potatoes and sweet potatoes, which makes all the difference when turning them into fries. Sweet potatoes have got a lot of sugary starch in them, which is released when they are baked, thus resulting in soggy fries. So, all you have to do to get them to crisp up, is to replace the sugary starch with a non-sugary starch, such as cornflour (cornstarch) or rice starch. That's all there is to it. We were so excited to have discovered this, that we made some sweet potato fries there and then.

Sweet Potato Fries
1) Peel and slice your sweet potato into evenly sized pieces.
2) Place the slices into a bowl of cold water and leave to soak for 20-30 minutes.
3) Pre-heat the oven to 220C / gas mark 8 / 450F
4) Drain the water from the fries and place inside a freezer bag.
5) Add a good shake of cornflour or rice flour and shake the bag until the fries are well coated. (I didn't measure how much cornflour I used, but I would estimate it was between 1 & 2 tablespoon's.)
6) Place the fries on a baking tray and spread them out. Lightly cover with sunflower oil. (Don't use olive oil, as this will create a lot of smoke.)
7) Bake for 20-25 minutes until crisp on the outside and soft on the inside.
8) Serve immediately with your favourite condiments!

Sidenote: I really wish that my Science teachers had taught me about the connection between food, baking and chemistry. I am pretty sure that it would have massively affected my lack of interest in Science at school if I had realised that the keys to baking are all in the chemistry. It is a helpful reminder that so much of teaching is about finding ways to connect with students in a way that is meaningful and applicable to them.


  1. Hi Ruth. Thanks so much for this post! I had the most sublime sweet potato fries when we were on holiday in the USA a couple of years ago and have tried to recreate them with the same results that you had {soggy!} I am definitely going to try them again this way.....


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