The Basic Recipe
Slice up sweet potatoes.
Coat them with olive oil and salt.
Cook them on trays in the oven, gradually lowering the temperature from 300 to 225.
The sweet potato
is the most nutritious of all common vegetables, and one of the cheapest. The orange varieties are often called "yams", but the true yam is a much larger root vegetable grown in Africa. The most nutritious way to cook sweet potatoes is by steaming or boiling, and it's possible you can preserve more nutrients by first steaming them and then drying them in a dehydrator. I tried that and they were too hard to chew, so now I just bake them dry in an oven. They do need to be cooked to deactivate trypsin inhibitors that block digestion of protein (source)
. Compared to commercial sweet potato chips, homemade chips are much cheaper, have more intense flavor, and you can use better oil.
How many you can make at once depends on how many trays you want to put in your oven. I use two large trays, which together hold about four small sweet potatoes or two large ones. I use a big knife on a cutting board and start by slicing them into rounds. When the diameter makes that difficult, I cut the potato in half lengthwise and end up with half-circles. The thinner and more uniform you can make them, the easier it will be during the baking phase. You might want to invest in a mandoline slicer, and then if you're at all clumsy, you'll also need steel or kevlar gloves to not repeatedly cut your fingers. You might also want to peel them. The peel is denser in nutrients but also contains stuff that's harder to digest.
Put the slices in a big bowl, throw in some olive oil and salt, and shake or stir them to mix. I like to have them slightly salty and lightly coated. Then spread them on trays to go in the oven. If some of your slices are much thicker than others, put the thickest slices in the corners of the pan. I always start with the slices overlapping, and then as they cook down I can spread them out so they no longer overlap. If your oven has convection, use it.
I start the oven at 300F for the first stage, which is driving off most of the water. About the time they shrink enough to be spread out, and the thinnest ones start getting brown, it's time to turn the temperature down to 275 or 250, and finally down to 225 for final drying. The whole process might take three hours. If you want to go faster you can keep the oven hotter and watch them very
closely, because there's a thin line between so undercooked that they're still chewy, and so overcooked that they taste burnt. In terms of color, they should be somewhere between dark orange and medium brown. Chips that are perfectly done will still be a little bendy when they're hot, and will turn crispy after cooling. Sometimes I'll take a tray out of the oven, pick out the ones that are done, and put the rest back in to finish.
I make chips in the fall and early winter, because I've found that in spring they have so much sugar that it's almost impossible to get them crunchy without burning them. This might be because starch turns to sugar in storage. Another issue is that sweet potatoes give most people gas. I've heard that the yellow/white ones are less gassy and also have less sugar, but they're hard to find for a good price.
It's surprising how much they cook down. Ten pounds will easily fit in a gallon sized ziploc bag, so they're a great road food.
(public domain, november 2012)