Sweet Potato Fries - The Quest for Crispy (FAK Friday)

Healthy Never Tasted So Good

I have a confession to make. I have never successfully made crispy sweet potato fries. Until now.

Every once and a while I come across a simple culinary task that renders me completely inept. I know plenty of people who turn out perfectly crisp sweet potato fries every time, with no fuss. Somehow, that's not the case for me. Instead they turn out limp, soggy, or a little burnt in an over-zealous attempt to crank the heat and get them crispy once and for all. And I know I'm not the only one.

A quick search turns up nearly a dozen different methods suggesting how to make perfect fries. I agree with many of them, in principal, and yet few have proved to be at all helpful. Finally I decided it was time I set out once and for all to solve this problem - for myself, and hopefully everyone else in my situation.


It's FAK Friday (Feeding my Appetite for Knowledge) and this week my diet has consisted primarily of sweet potatoes, as I attempted again and again to produce the perfect fry. Now that I've done my share of tests, I'm sharing my findings in the hope that my experiences may shed some light for anyone else struggling with this simple spud.

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The Quest for Crispy

Sweet potatoes - not yams

First off, let's get something straight. Sweet potatoes are not the same as yams. Here in the US, they are frequently (miss)labeled as yams - but just because the label says it doesn't make it so. In fact, real yams, native to Africa and Asia, are of a completely different genus than sweet potatoes, and have an almost black outer skin similar to the bark of a tree.

While we're at it, did you know that sweet potatoes aren't even related to regular potatoes? They're from two different families entirely, and while there are hundreds of varieties of potatoes, the sweet potato isn't one of them. While regular potatoes find themselves sharing genes with tomatoes, peppers, and eggplants, sweet potatoes are more closely related to morning glories, a type of flowering vine. In other parts of the world sweet potatoes go by a range of different names, one of which being "batata", a word which later morphed into the already well-known "potato". Thus was born, the sweet potato. Who knew?

Okay, enough with the history lesson. On to the fries!

Let me start by saying you can make sweet potato fries by deep frying them, just like regular french fries... but for this experiment, I'm going to focus on how to get them crispy in the oven. Not only are oven-baked fries significantly healthier, but who wants to burn a half gallon of oil just for a snack? Not me, that's who.

Just to clarify, when I say crispy, I mean similar in texture to a regular french fry - a bit of crisp to the outside, with a soft interior. 

In order to figure out the best method, I went out and bought a bunch of sweet potatoes. I used a mix of both Garnet and Jewel, in case the variety made a difference. (It didn't, though I found I liked the Garnet a bit better in flavor.) I researched every tip, trick, technique, and recipe I could find. Then I set to work testing each one. I tried them all with a range of different oven temperatures, as well as different thickness of potato, to see what would work the best.

                       Mushy Inside                                   Burnt                                     Just About Right

I did a total of about seventeen tests. I won't burden you with a detailed account of each one, but here are some of the highlights.

I started by doing what most people do - slice a potato, drizzle with olive oil, sprinkle with salt, and bake. Easy peasy, as it should be. I tried many variations on this, lining my tray with parchment or foil, using more or less oil, cutting the fries thicker/thinner, baking at different temperatures... I learned a lot about what worked and what didn't, but I still wasn't getting a crispy exterior. I even tried one method which suggested turning on the broiler for the final moments of baking, which turned my fries completely black (see the middle image above).

Next I tried a few different recipes which called for soaking the fries in cool water for awhile, then rinsing and drying them before baking. The idea behind this method is that soaking will draw out some of the starches from the potato. Starch holds on to moisture, so less starch means a less soggy fry, right? It made plenty of sense to me, but my sweet potatoes didn't agree. I found zero difference in the crispiness of the fries, and am pretty sure the insides were actually a little soggier than before. Almost as if they'd been sitting in water for a long period of time... strange.

Next I moved on to coatings. There are two main "techniques" out there for coating the fries. The first is to toss the fries in a lightly beaten egg white before baking, the theory being that the egg white will do the crisping, and act as a shell on the outside of the fry. I don't like this method for a few reasons: one, I don't particularly want to whip an egg white just to make some fries; two, it takes a perfectly good treat that can be enjoyed by anyone and makes it off-limits to those on diets or with egg allergies; and three, it simply doesn't work that well. The egg white does become crisp, but it ends up tasting more like over-cooked scrambled eggs with a soggy fry in the center. Not the desired result, in my opinion.

The second "coating" method is to dredge the fries very lightly in cornstarch. This goes by similar logic to the egg white version, but unlike the egg white the cornstarch actually clings to the fries and helps absorb some of the moisture that comes out of them. I played around with this technique for quite a while, trying to get just the right amount of cornstarch (too much means gummy, yucky fries), before finally getting it to work the way it's supposed to. While the cornstarch did create a somewhat pleasant texture, I found it left the fries with an odd flavor similar to that of raw flour, and a very greasy feel. Perhaps with heavy enough seasoning, this would be acceptable. (I should note, making a batter of cornstarch is a great method for getting extra crunch on deep-fried fries, but I found it didn't work nearly as well in the oven.)

Just when I thought I had run out of ideas, it occurred to me that the problem might lie not in the technique I used, but the equipment. Was it possible my oven was the issue? Surely a convection oven would do a better job, but that couldn't be the only answer. What about water vapor, which can sometimes be an issue in gas ovens? That couldn't be it, because mine is electric. Still, I couldn't help but wonder...

So I called up a friend of mine - one of those lucky people who make sweet potato fries all the time with no problems - and asked if I could borrow his kitchen. Well, he did me one better, and not only let me use his kitchen but walked me through exactly how he did things.

And you know what? He did them exactly the same way I (normally) do. Cut the fries, toss 'em in oil, and bake. I measured the temperature of his oven, cut the fries as I had been, and baked them exactly the same way... and low and behold, they came out much more french-fry-like than the ones I had made before.

The biggest difference between the batch at my friend's house and the batch at my house? The baking sheet. My baking sheets are rather thin, and have a black non-stick coating. His trays were much heavier-bottomed, and had no such coating. This created a much more even heat, and a much crisper caramelization on the outside of the fries.

Perfection!

I wish there were some grander finale to this tale than a baking sheet, but sure enough, those fries were perfect. I made batch after batch, and each time was the same. So what about you - do you have trouble getting crispy fries, and if so, what type of tray do you bake them on? I'd love to know if my theory is right!

Along my little journey, I learned a lot about what did and did not work. I know I've been a little round-about in getting to it, but here are my top tips for making perfect sweet potato fries:

How To Make Perfect Sweet Potato Fries

Tips, Tricks, and Techniques

1. Preheat the oven -  I found my fries baked perfectly between 425f. - 450f.. This temperature may vary depending on your oven, and also the pans you bake your fries on. I found with a black, non-stick coated pan, 425f. was plenty hot enough. With a thicker, non-coated pan, 450f. was the right temperature. Use an oven thermometer to make sure the temperature is correct - it isn't uncommon for an oven to be as much as 30-40 degrees off.
2. Use the right baking sheet - I found that a heavy-bottomed baking sheet with a shinier (not coated) surface did the best job making crispy fries. If you're using a flimsier tray, try reducing the oven temperature a little and increasing the bake time.
3. Cut the potatoes into evenly sized fries - this way they cook at an even rate. I found that the best size was just under half an inch thick. Much thicker and they didn't get crisp, much thinner and they burned. Peeling the potato first is up to you, but keep in mind there's a lot of good flavor (not to mention nutrients) in the skin. I also found the skin gave a better crunch to the fries. Just be sure to wash your potato and dry it well if you plan to leave the skin on.
4. Use enough oil - one of the main reasons to make fries in the oven instead of the fryer is because they're so much healthier, but that doesn't mean you can avoid the oil all together. It does mean you can use healthier oil, though, like olive oil or coconut oil. Once the fries are cut, toss them in 1-2 TBSP to coat. Be sure to grease the pan, too, to keep them from sticking (or you could use parchment paper - I found it didn't make much difference in terms of crispiness). 
5. Seasoning - After coating the fries in oil is the perfect time to season them, because the oil will help it stick. A pinch of salt is a must, but the flavor possibilities are truly endless. If you're in the mood for something spicy, try a bit of chili powder or cayenne pepper. Want something sweet? A dash of cinnamon goes a long way. Some of my favorites are cumin and coriander, rosemary or sage, curry powder, paprika, garlic powder, and even nutmeg. Use whatever flavors call to you!
6. Spread the fries into an even layer - space the fries out on the baking sheet with a bit of room  between each one. If the fries are crowding the pan they'll steam themselves and become soggy instead of crispy. If you're making a lot of fries, use two trays, or do them in batches. (Don't put more than two trays in the oven at once, or else the amount of steam may cause them to get soggy.)
7. Bake in the upper 1/3rd of the oven - you want the oven to be hot, but if the fries are too close to the heating element (at the bottom of most ovens) they may get burnt. I found keeping them on the top, or second to top rack, helped tremendously.
8.  Flip the fries every 10-15 minutes - this will help them cook evenly, and also ensure they get caramelized all 'round. The side of each fry touching the pan will have the most browning, while the side on top will have a chance to dry out and release steam. Both are important! If you're using two trays, be sure to swap their positions in the oven at this time, too. (I found my fries took about 30-35 minutes, though your time may vary depending on your oven, baking sheet, and the thickness of your fries.)
9. If you're using a gas oven - depending on your oven, you may find it necessary to crack the door ever few minutes, just for a moment, to let some of the steam out. Don't leave the door open for a long period of time, though, because you don't want the heat to dissipate!
10. Once the fries are out of the oven - move them immediately to a cooling rack so that air can circulate around them. Keep them spaced out in a single layer (not piled on top of each other) so that they'll hold on to the crispy exterior.
11. Devour immediately - it doesn't need to be said, but fries are best eaten fresh. Fresh, and before anyone else has a chance to get to them. 

So there you have it... no fancy tricks, just a little practice and the right equipment. Do you have any tips for making fries? Have you struggled with them in the past, and if so, was any of this helpful to you? Oh, and what's your favorite seasoning to use? I'd love to know in the comments below!