baked purple sweet potatoes

How To Cook a Purple Sweet Potato: Recipe & Nutrition Benefits

[toc]If you don’t have the ORAC chart memorized, there is an easy trick you can use at the grocery store to buy the most nutritious foods for antioxidant content. The more colorful they are, the healthier.

That’s usually how it goes.

There are some notable outliers, like eggplant. It’s not that its ORAC value of 932 is “low” per se, but rather one would expect it to be a number that’s higher than a white potato at 1,058. But there’s a good explanation in this case… even though the outer eggplant is a vibrant purple, the inside is pale white. Therefore when you average it out, its value isn’t that high.

That’s not the case with the beautiful purple potato, which is just as vibrant on the inside as it is on the outside. Do they lose their color after you cook them? Nope, even after 2 hours in the oven, these spuds are violet as ever.

Health benefits

Their vibrant color explains why the ORAC value of purple sweet potatoes is so high, coming in at 2,720, at least in their raw form (tests on the cooked version have not yet been published).

To put that number in perspective, blueberries are 4,669. The purple taters are almost 60% there. That’s a lot of antioxidants!

Of course it’s not always easy to find them at the store. This is especially true since the pandemic, as supply chains have been interrupted. Can’t find them fresh? Try purple sweet potato powder from Amazon.

Like blueberries, these spuds have a high amount of anthocyanins. Depending on the plant’s pH, those create the blues, reds, and/or purples. There are many different types of anthocyanins and in these potatoes, the two in highest concentration are peonidin and cyanidin. These are responsible for producing much of their antioxidant content.

Stokes Purple Sweet Potatoes Nutrition Facts
Serving Size: 110g (about 3.9 ounces)
Calories 130
Calories From Fat 0
% Daily Value* % Daily Value
Total Fat  0g 0% Vitamin A  100 IU 2%
Trans Fat  0g Vitamin C  12mg 20%
Sodium  0mg 0% Calcium  40mg 4%
Total Carbs.  28g 9% Iron  1mg 6%
Fiber  4g 16%
Sugar  4g
Protein  2g
*Percent Daily Values (DV) are based on a 2,000 calorie diet

With low amounts of sugar and very reasonable amounts of carbs, these spuds are a healthy choice even if you’re on a diet. You’re really getting a lot of food relative to the calorie count.

Generally, sweet potatoes and yams have a lower glycemic index rating (GI) than white, russet, and red potatoes. That’s good for everyone, especially type 1 and type 2 diabetics. However we are not aware of a reputable source for the GI of purple sweet potatoes (if you know, please mention in comments). Whatever the case, most likely these violet beauties are better for you if you have diabetes, when compared to the boring whites and redskins.

Since the purples are more of a niche food, they haven’t been studied as extensively for health benefits. However there was a study published in 2013 which suggested purple fleshed potatoes may help protect against colon cancer (1).

Here’s how to make a delicious and low calorie oven-baked sweet potato. Boiling is another option, more on that below.

The healthiest recipe for you

Step 1: Buy the potatoes

bag of Frieda's Stokes purple sweet potatoesOkay normally in a recipe, it would be stupid to list “buying” as a step, but this isn’t a normal food.

These aren’t easy to find. As is the case with most root vegetables, regular potatoes are something that can be grown pretty much anytime. Not so with sweet potatoes. Their origins are Central and South America so they’re a tropical plant and like it hot!

For that reason, it’s not easy to grow them year ’round in the United States. They can’t tolerate frost. They need lots of sunshine and warm nights, growing best at an average temperature of at least 75 °F. They mature in 2 to 9 months. We need to use early-maturing cultivation methods since 9 months would be too long here due to the changing seasons. For these reasons, the purple sweet potato growing season only runs during the summer months in most of the country.

The bag you see pictured was purchased at Trader Joe’s in Manhattan Beach, CA (Los Angeles). The produce company is Frieda’s and they are organic. At a cost of around $3 they were a great deal! Surprisingly these were purchased early in the year, at the end of March, and yes they were grown domestically. The bag didn’t say where.

Trader Joe’s only carried them for a couple weeks and they haven’t had them for over a month now.

Where can I buy purple sweet potatoes now? Good question. At the Whole Foods in El Segundo (LA) they’ve never been seen, no matter what time of year it is. Despite being one of – if not the – largest Whole Foods in LA, their management is a bunch of buffoons and there are many items they don’t carry which the smaller locations nearby do. Perhaps better luck at the Whole Foods in your city?

nutrition of Stokes vs. Okinawan vs. orange potatoes

These, the Stokes variety, should be your first preference. They have the richest purplish hue. They are the healthiest sweet potato, inching out the Okinawan and obliterating the traditional orange sweet potato or yam.

The history of Stokes purple is as bizarre as they are delicious. Mike Sizemore, a North Carolina farmer, won a prize at the state fair for a different type of potato in 2003. Supposedly – or so his story goes – an unidentified lady there gave him one of these, without saying where it came from. He cultivated it. Lo and behold, it turned into a 2nd career for him. Prior to that, he spent 3 decades in law enforcement catching car thieves.

While not as pretty or nutritious, you could settle for Okinawan or Hawaiian purple sweet potatoes, which seem to more readily available and can even be found for sale online if you’re willing to pay the shipping.

Step 2: Preheat the oven NOT per instructions

preheating over to 275 degreesOn the Frieda’s bag you will see instructions for heating them at 350 degrees. If you enjoy eating potentially carcinogenic substances, then go ahead and do that.

Acrylamide is classified as Group 2A carcinogen by the International Agency for Research on Cancer (IARC), which is part of the World Health Organization. It’s found in most carbohydrate-rich foods when they are cooked. Avoiding it completely is impossible, but you can greatly reduce its formation by:

  • Cooking at lower temps, ideally below 300 degrees
  • Not allowing carb-rich foods to dry out

Baking at less than 300 degrees may seem impossible for a lot of foods but trust us, it isn’t. Everything from Christmas cookies to pizza (homemade dough and all) we regularly make without any trouble, using temperatures in the mid 200’s. The trick is you just have to plan for more time. More on that in a minute.

For this recipe, we used 275. If you have the time, doing 250 for longer may be better for you.

Step 3: Rinse the potatoes

Clean the spuds off while you’re preheating. They’re pretty clean to begin with.

raw Stokes purple potatoes

With the Frieda’s brand at least, there was no dirt residue. The only things that really needed attention were the little hairs or strings, which are actually tiny root remnants left over that you will find on not just purple yams, but all yams.

BTW we know yams and sweet potatoes are technically different species. But several decades ago, the USDA “officially” declared there to be no difference between yams and sweet potatoes, at least in terms of their marketing. Since then, the public uses the terms interchangeably and for that reason, we do too.

rinsing potatoes in sink

Step 4: Put in glass casserole dish with lid

Foil? Not here. Most recipes for oven baked purple sweet potatoes are one of the following:

  • Slicing, dousing in oil, and placing in a baking sheet or dish
  • Individually wrapping each potato tightly in foil
  • Putting them in the oven unwrapped, without foil

All of these are a total disaster for your health. Openly cooking them on a cookie sheet or in a dish has a drying effect. Remember the acrylamide.

With the exception of certain acidic foods like some tomatoes, foil is perfectly fine (and we use it a lot) for wrapping cold foods for storage in the fridge – i.e. covering a bowl or plate. However when you heat foil as well as aluminum pots and pans, higher amounts leach into your food (2) (3) (4; big PDF, loads slow).

They tell us that’s perfectly safe, is it?

For many decades, there has been quite a bit of research suggesting aluminum (AI) may act as precursor or contributor to Alzheimer’s disease (5). You’ve likely heard that. But if we had to bet on that, we would actually say it might not. Why? Because most of the studies, especially the earlier ones, had assumed correlation = causation. In other words, they assumed the higher amounts of AI present were causing the Alzheimer’s.

cross section of raw purple potato
cross section view of raw potato

More recent data, at least in our opinion, suggests that the higher levels of aluminum *might* be due to the changes in brain structure from the disease. In other words, it may not be causing the disease, but rather the disease is causing more AI and other compounds like copper and iron to accumulate in the plaques and tangles, which represent the hallmarks of the diseased brain (6). If anything, the copper appears to be more of a concern than the increased AI. It might be a situation where correlation ≠ causation. That said, recent studies continue to support the theory that higher exposure to AI = higher Alzheimer’s rate (7) (8). Both sides make good points, no one really knows.

To veer on the side of caution, we prefer to cook with clear glass instead. In theory at least, ceramic bakeware is fine too, except you don’t always know with the made-in-China rubbish what exactly is in its glazing… are there higher amounts of heavy metals present?

And refined oils? Those are not healthy, not even olive oil, but that’s too big of an argument to have here. Since most people tend to care about their vanity way more than their health anyway, we will just make our oil-free appeal based on that motive because…

  • 1 serving of 3.9 ounces (about 1 potato) = 130 calories
  • 1 tablespoon of olive oil = 120 calories

By using oil, you may be doubling your calories. It’s pure fat. Even light oil use is likely an increase of 50%. Plus that’s not even counting any oil/butter you smother on after (butter is still 102 calories per tbsp).

If you’re struggling with weight loss, these nutrition facts should make the no-oil decision obvious. But even if you’re not dieting, wouldn’t you rather eat up to 2x that amount of spuds for almost the same amount of calories? Being the pigs we are, that’s how we roll at Superfoodly.

Speaking of pigs, the one below looks like he’s about to eat them…

casserole dish of raw purple yams

Fill the dish with a couple inches of water, this will keep the sweet potatoes moist throughout and with the lid closed, will have a steaming effect.

If your home’s water is unfiltered, bottled may be preferable depending on your water quality. If you live in the middle of nowhere with clean well water (i.e. no pesticide contamination from farms), then likely your faucet H20 is better for you than getting it from a plastic bottle.

Step 5: Put in oven

Stick ’em in on the middle rack or slightly higher.

yams in oven

How long do you cook them?

The total cooking time will vary based on how many there are (density of contents) and the type of casserole dish you use. Expect anywhere from 2 hours and 15 minutes, up to 2 hours and 45 minutes.

Before you say that amount of time is ludicrous, keep in mind the original instructions (at 350) call for up to 2 hours. Regardless of the temperature, you have to cook these significantly longer versus white potatoes and traditional orange sweet potatoes.

How long do you boil purple sweet potatoes? That’s a shorter amount of time, 45 to 60 minutes. However we are far too lazy to deal with stirring a pot and cleaning up water that spills over the side. You may be a better cook, but don’t lie you know it happens to the best of us, especially with the high BTU gas burners.

Check them periodically, say every 20 to 30 minutes. Shuffle them around a bit, bringing the potatoes from the bottom to the top. Refill the water as needed, so there’s always at least an inch of it.

The great part about baking at 250 degrees is that it makes it very hard to burn/overcook the food. So you can be busy doing other stuff and not freak out if you forget to check them.

Step 6: Confirm they’re ready

Here they took about 2 hours and 30 minutes. When ready, this is what they look like…

cooked yams fresh out of oven

You know they’re done when they’re easily falling apart…

fully cooked yams

If in doubt, plop a purple yam on a plate and cut it open..close up of a cooked purple yam

Step 7: Time to eat!

Before serving, some of the ends you may want to cut off. Not only will they be less appetizing due to their texture, but also they’re the driest part of the potato (and hence, have the highest acrylamide concentration).

burnt ends of potato

There are two reasons why it’s better to cut the ends off after baking instead of before:

  • The potatoes are more prone to fall apart once you cut them.
  • Exposing the inside of the potato would lead to drying.

How do you eat them? However you want! Just don’t smother in oil/butter or we will smack you.

These were used for a simple dinner. A plant-based macrobiotic meal consisting of nutritious high-protein grains and legumes; rainbow quinoa, buckwheat, and lentils. In the top right is a basic wild mushroom medley with minced garlic. A simple arugula salad with yellow cherry tomatoes and a zero calorie coconut vinegar dressing.

vegan gluten free meal close-up photo

Oh and about that missing butter/oil, with this recipe you will be left with something that tastes so moist and juicy, it’s the next best thing to having an extra 120 calorie tablespoon of oil on it. Even naked, they taste amazing!

vegan gluten free meal photo

If you want to jazz up the taste without upping the calories, sprinkle some cinnamon and nutmeg on these purple sweet yams. Seriously, it makes them taste like a dessert. If you’re not dieting, toss a few crumbled raw walnuts on. All three of these add-ons have extremely high ORAC values.