Sweet Potatoes vs. Regular Potatoes: Why Are They So Sweet?

When you walk through the produce section, you see Russets, Yukon Golds, Red potatoes, and Fingerlings. Most people assume these are all entirely different plants. In reality, they are the exact same botanical species (Solanum tuberosum). They’re merely different cultivars of the plant; specific varieties that humans have selectively bred over centuries for different starch levels, skin thicknesses, and colors. But sitting right next to them in the grocery bin is the ultimate botanical imposter: The sweet potato.

Despite the name, the sweet potato (Ipomoea batatas) is not a potato at all. It isn’t a different cultivar, a different strain, or even in the same botanical family. Regular potatoes are members of the Nightshade family, alongside tomatoes and eggplants. Sweet potatoes are members of the Morning Glory family. Because they evolved entirely separately on the botanical family tree, they process energy differently. So, they are allowed to be sweet without owing any apologies to regular potatoes.

🍿 Speaking of Botanical Imposters… If you think the sweet potato is a mind-bender, wait until you look at the snack aisle. Most people assume popcorn is a bizarre, engineered anomaly of “regular” sweet corn. The botanical truth? It is the exact opposite. Discover why the corn on your dinner plate is the actual fragile mutant, and why popcorn is the ancient, armored survivor.

The Botanical Breakdown: Species vs. Cultivar

The sweet potato gets to break the rules, but what are the rules? Let’s look back at our standard grocery store potatoes.

Solanum tuberosum is the potato species. It’s the fundamental, genetic blueprint of the potato plant as it exists in nature. But humans rarely leave nature alone. When farmers intentionally and selectively breed that base species over generations to lock in a specific trait, like the thick, baking-friendly skin of a Russet or the buttery, yellow flesh of a Yukon Gold, they create a cultivar (a mashup of the words “cultivated” and “variety”). A cultivar is an engineered plant that relies on human intervention to exist and propagate.

You will often hear people call a Russet a “variety” of potato. Botanically speaking, that is technically incorrect. A true variety is a variation that happens naturally in the wild, without any human help. However, because the general public uses the terms interchangeably, the produce aisle can feel like a botanical wild west.

The key takeaway is this: Russets and Yukon Golds are different human-made cultivars of the exact same species. But the sweet potato isn’t a different cultivar. It isn’t even a distant cousin. It is an entirely different species from an entirely different family.

So, What Actually Makes the Sweet Potato Sweet?

Because the sweet potato evolved on a completely different branch of the botanical tree, it developed an entirely different chemical toolkit for storing and processing energy. While regular potatoes lock their energy up in bland, rigid starches, the sweet potato acts as its own internal sugar factory.

Like a potato, sweet potatoes contain most of their carbohydrates in the form of starch. Starch is a way for the plant to store sugar, by connecting saccharides together in long, branched complexes. Starches, unlike simple sugars, which have only one or two saccharides (sucrose or table sugar has two), do not taste sweet, but deliver a huge carbohydrate punch because our bodies can use digestive enzymes to break them down into simple sugars. Sweet potatoes themselves have a lot of enzyme systems that are responsible for various functions, including degradative ones, within the root.

One of these enzymes is the same kind of enzyme that we use to digest starches: Amylase. In fact, sweet potatoes have so much amylase, in the form of alpha- and beta-amylase, that they are used to produce commercial enzyme preparations. All of the commercial production of beta-amylase in the U.S. comes from sweet potatoes. These amylase enzymes break down a type of starch called amylose. That makes sense, right? The enzyme that breaks down amylose is called amylase.

You will notice that different sweet potatoes have different degrees of sweetness when raw. Some of them are hardly sweet or not sweet at all, while others can be fairly and pleasantly sweet even before cooking. This has to do with the cultivar (variety), and the levels and activities of the amylase enzymes during storage. The way the sweet potato is stored, the temperature, etc., can also influence this. There are other enzymes, as well, that can influence the taste by affecting mouth-feel.

Now, all this enzyme activity, being degradative, means that while the potatoes might get a bit sweeter during storage, other not-so-desirable things can happen as well. Once they start going bad, they go bad very quickly and you really can’t save a sweet potato once it seems like it has begun to rot. Just because you cut off the bad part, the rest of the flesh will be wonky, and texture and taste will be bad. So don’t bother. Store them in a dry place at about 50 to 60°F, by the way. And, like actual potatoes, never wash them until you are about to use them.

But of course, once you cook a good sweet potato, even if it’s not so sweet to begin with, it gets much sweeter. This is because the amylase is more active at higher temperatures, so when the potato starts cooking. the amylose starch really starts breaking down much faster into a simple sugar called maltose.

How to Make Sweet Potatoes Sweeter When Cooking

You can influence the sweetness of the final result with the way you cook the sweet potato. The faster you cook it, the less sweet it will be. The faster the cooking time the less time the enzymes have to break down the starches. For the sweetest taste, you want to bake them in the oven.

Although you’d have to taste it to know how sweet a particular sweet potato is before you cook it, there are a couple of rules of thumb. There are two basic types. One has pale yellow skin and flesh, and the other has dark orange or red skin with deep orange flesh. The darker orange ones tend to be a little sweeter than the pale ones. Keep in mind that within these varieties the colors can vary from an almost white to a deep orange or red. There are even some with a purplish skin. Still, all sweet potatoes are sweet once you cook them.

Botanical FAQ: Decoding the Produce Aisle

If you want to get technically accurate with your gardening terms, here is a quick breakdown of how botanists classify the plants we eat.

Q: What is a Subspecies? Think of a subspecies as a major geographical split. It happens when a single plant species gets physically separated (by a mountain range or an ocean) and evolves slightly different traits to survive in its new environment. They are still the exact same species and can easily interbreed, but they have distinct, localized differences.

Q: What is a true Variety? Unlike a cultivar (which is bred by humans), a variety is a natural mutation that happens in the wild, effectively acting as a smaller, localized off-shoot of a subspecies. If a patch of wild white-flowering plants naturally produces a plant with pink flowers, and that pink-flowered plant successfully reproduces on its own in nature, it is a variety.

Q: What is the difference between a Cultivar and a Hybrid? A cultivar is simply a plant bred for specific traits. A hybrid is a highly specific type of cultivar created by cross-breeding two completely different species or distinct parent lines together (like crossing a grapefruit and a tangerine to get a tangelo). Hybrids are often sterile or produce highly unpredictable seeds, meaning humans have to constantly re-cross the parents or use cuttings to keep the hybrid in existence.

Q: Are all cultivars dependent on humans to propagate? Yes, absolutely. By definition, a cultivar only maintains its specific traits because humans are actively managing it (usually through grafting, taking cuttings, or highly controlled seed saving). If you were to abandon a cultivar in the wild, one of three things would happen: it would die because it lacks natural defenses, its seeds would revert to a chaotic wild form over a few generations, or (in rare cases) it would successfully naturalize and reproduce on its own. If it manages to survive and reproduce independently without losing its traits, botanists would actually stop calling it a cultivar and reclassify it as a true, naturalized variety.