White Sweet Potatoes Aren’t Less Sweet Because They’re White: In a 15-Variety Baking Test, a Japanese Type Ranked Among the Sweetest
White sweet potatoes aren’t less sweet because of color: a 15-variety baking test ties sweetness to starch and one enzyme. Types, growing, curing and fixes.
In a USDA and NC State test that baked 15 sweet potato types whole, the two sweetest were an orange variety, Covington, and a Japanese type that the researchers group with the white and cream varieties. One of the two least sweet was a breeding line with 37.2% dry matter that made less than 2 mg of maltose per gram of root. Flesh color didn’t sort the sweet from the bland. Starch and a single enzyme did most of the sorting.
The usual story about white sweet potatoes is that they’re drier and therefore blander. The first half holds up for some types, especially boniato. The second half doesn’t hold as a rule, and the reason changes what you should grow, how you should cook it and what you should expect from it.
One caution up front: this is one trial of 15 genotypes with a single Japanese type in it. It’s strong evidence for the mechanism, not a ranking of the roots in your grocery store. Where the sources disagree, the tables below show both sides.
What Counts as a White Sweet Potato
Five kinds of root get sold under this name, and they differ in the garden and in the oven. The table below uses the breeders’ own plant-patent filings, Florida Extension and the NC State test.
Skip the guesswork — get a pre-planned 4×8 kitchen garden bed
Free printable planting plan: what goes where, when to plant it, and how to keep it alive. Plus two bonus flower bed plans.
| Type | Skin and flesh | Cooked character | Garden notes |
|---|---|---|---|
| O’Henry | Light tan to brown-toned skin; white flesh with an orange cast or streaks (per the Louisiana filings) | Sorted with the US white/cream cluster in the NC baking test | A white-flesh mutation of Beauregard; susceptible to southern root-knot nematode |
| Bonita | Light tan skin with a pink cast; bright white flesh with a yellow cast | Drier than O’Henry (breeder’s filing); same US white/cream cluster | Bred in Louisiana as an O’Henry alternative: better nematode resistance, higher yield |
| Murasaki-29 | Deep purple skin; white flesh | High dry matter (breeder’s filing) | Better nematode resistance than Beauregard; soil rot and Fusarium root rot resistance similar to Beauregard |
| Japanese types (Kokei No. 14 in the NC test) | Skin not described in the study | Cohesive, uniform texture; one of the two sweetest baked | Sweetness varies a lot by Japanese variety (see below) |
| Boniato (Cuban sweet potato) | Reddish-brown to burgundy skin; bright white, “very dry” interior | Drier, fluffier and less sweet than orange types; chestnut-like | 120–180 days to harvest; hard for home gardeners to source; tender and short-lived in storage |
Only boniato is described as dry and less sweet by an extension source. For the US types, the documented differences are disease traits and flesh shade. Purple skin doesn’t mean purple flesh either: Murasaki-29 is purple outside and white inside.
Retail names such as “Hannah” show up in grocery stores too. We found no university release record for it, so what’s written about it online is seller description, not trial data.
Sweetness Comes From Maltose, and Color Isn’t in the Chain
A baked sweet potato tastes sweet mostly because heat turns its starch into maltose, and that conversion needs two things: enough starch and a working enzyme called β-amylase. Flesh color isn’t one of them.
The raw roots in the NC test had no detectable maltose. Baked, the same roots held between 0.8 and 108.2 mg per gram. As the oven heats a root, its starch gelatinizes (swells and loosens), and β-amylase chops the loosened starch into maltose. Japanese researchers point out the enzyme can’t digest raw starch, which is why most of the maltose appears in the oven, not in the ground.
Starch is the raw material. After two enzyme-dead lines were set aside, maltose in the baked roots tracked starch content closely (R² = 0.90). The same starch also makes a root denser: in the NC panel, higher starch meant lower perceived moisture (R² = 0.64) and more mealiness (R² = 0.68). On this evidence, the trait that makes a root feel drier is also the trait that gives it more sugar to make, provided the enzyme works.
The enzyme is the catch. Two lines in the NC test had β-amylase activity below 10 units per 100 g, and both made under 2 mg/g maltose. One of them, NCDM04-001, was the 37.2% dry matter line from the opening, and it ranked among the least sweet. Japan has the same problem in its own varieties. ‘Satsumahikari’ (released 1987) and ‘Okikogane’ (2002) steam to only about 7–9 Brix because almost no maltose forms, and the missing-enzyme trait is a single recessive allele that turns up often in breeding stock. A starchy root with no working enzyme is bland, and you can’t see that from the outside.
| Factor | Role in baked sweetness | Evidence | Does flesh color predict it? |
|---|---|---|---|
| Starch content | Raw material for maltose | Maltose vs starch R² = 0.90 with active enzyme (NC State/USDA) | Loosely: in a 13-genotype Ghana panel, deeper orange meant lower dry matter |
| β-amylase activity | The converter; near zero in “null” lines | Under 2 mg/g maltose in both null lines; single recessive allele (Japan) | No link reported |
| Starch pasting temperature | Lower temperature, more maltose | r = −0.53 across 221 samples (Japan) | No link reported |
| Texture and particle size | Changes how sweet the same sugar tastes | Sweetness depended on both sugar and texture (NC State/USDA) | US white/cream types clustered together: cohesive, uniform, small perceived particles |
The only color pattern in this data is indirect: deeper orange tracked lower dry matter in the Ghana panel, which, on the starch logic above, would mean less raw material to convert (that’s our inference, not a finding of that study). Orange isn’t a handicap either: Covington was the other of the two sweetest roots in the NC test.
Raw sugar counts mislead for the same reason. The deep-orange Ghanaian line Apomuden had the highest total sugar of its panel (36%) and the lowest dry matter (20%). In the NC test, total sugar in the baked root explained only about a third of the sweetness scores (R² = 0.34); weighting each sugar by its sweetness raised that to 0.60, and texture covered part of the rest. “Which root has more sugar before cooking” is a poor guide to “which tastes sweeter baked.”
Where the Dry-and-Bland Reputation Comes From
The reputation is right about texture for some types and wrong as a rule about sweetness. In the NC test, the orange Beauregard and Covington formed their own texture cluster: high in perceived moisture, fibrous, low in mealiness and firmness. The US white/cream types (Bonita, O’Henry and the Japanese type) formed another: cohesive, adhesive (sticky) and uniform, with a small perceived particle size. The mealier, firmer, less moist cluster was represented by Dimbuka Bukulula, not by any of the US white types.
Dryness is documented for boniato (Florida Extension calls the interior “bright white, very dry”) and for Bonita relative to O’Henry (the breeder’s filing). The NC panel doesn’t call the US white types dry. Most of the dry-and-bland reputation seems to come from boniato and from high-starch, low-enzyme lines, not from white flesh itself.
Even the textbook explanation for dryness is contested. The tidy version says dry types carry less amylase. The sources don’t agree:
| Source | What it reports | What it implies |
|---|---|---|
| Allan et al. 2024 (summarizing earlier work) | “In general,” higher starch and dry matter, lower amylase activity and higher gelatinization temperature tend to give dry, firm roots | Dry type, low amylase |
| Shin and Ahn 1987 (Korea) | The dry-type ‘Wonki’ had more starch and higher amylase activity than the moist-type ‘Chunmi’, and gelatinized later; the hardness gap vanished once both were fully gelatinized | Dry type, not low amylase; how far the starch has gelatinized matters |
| Nakamura et al. 2018 (Japan) | Across Japanese cultivars, maltose rose with β-amylase activity up to a threshold, and “null” variants exist | Check the enzyme, not the dryness label |
The practical takeaway: “dry” describes the texture you get, not the sweetness you’ll get. Two roots can both bake dry, and one can still be far sweeter.
One more nuance from Japan: breeding changed the answer within the same country. The 1945 variety ‘Kokei 14’ and 1960’s ‘Tamayutaka’ made under 10% maltose in steamed roots, while ‘Beniharuka’ (2007) and ‘Himeayaka’ (2009) made over 12%. Variety, not color, is the variable. (In the NC panel, Kokei No. 14 still ranked among the sweetest; the two studies used different panels and cooking methods.)
Bake It Whole and Slow
To get the sweetness a variety is capable of, bake it whole in its skin, and give it time. The NC test wrapped each root in foil and baked it for 60–75 minutes at 370°F (188°C). That slow heat-up gives the starch time to gelatinize and the enzyme time to work.
Stop buying the wrong pot size.
Enter plant type and growth goal — get exact pot diameter, depth, and volume before you spend a cent.
→ Find the Right PotA 2017 Chinese study compared baking (392°F/200°C for 45 minutes), boiling and steaming on four non-white cultivars. Every method cut α-amylase activity sharply, baking lost the least starch, and it produced the largest maltose gain in the yellow-fleshed Jinyu (+240 mg/g dry weight). That paper’s text and tables disagree in places, and it tested no white-fleshed type. We found no study that baked, boiled and steamed a white type side by side, so treat “bake whole” as a well-supported default, not a proven white-type rule.
If you’ve never tasted a variety, bake one root before you plan a dish around the harvest. Florida Extension compares boniato’s flavor to chestnuts, so judge it as a savory root, not a dessert one.
Growing White Types: What Changes From the Orange Playbook
Very little changes in the field. What changes is where you get slips, how long the season has to be, which pests you can live with and how long the harvest keeps.
Planting is the same. White types start from slips, go in when the soil is warm (our guide to planting sweet potato slips when soil reaches 70°F covers the trigger), and need the same space: Florida’s handbook gives 10–12 inches between plants and 36–48 inches between rows. Boniato can also start from 8- to 10-inch vine cuttings planted 12 inches apart. If you want to raise your own plants, see how to grow sweet potato slips. Our full sweet potato growing guide covers the rest of the season.
Sourcing is harder. Florida Extension says home gardeners will find it difficult to get boniato roots or plants, and that red-skinned, white-fleshed sweet potatoes bred in other states may be available from their breeders or through certified slip producers. Buy certified slips of a named variety. For the orange side of the comparison, see our sweet potato varieties compared.
Season length is the sticking point. The sources measure different things, so they don’t line up:
| Source | Days | What the number describes |
|---|---|---|
| UF/IFAS boniato publications | 120–180 (average season 150) | Harvest after planting, South Florida boniato |
| UF/IFAS vegetable handbook | 85–130 | Days to maturity listed for sweetpotato/boniato together |
| NC State/USDA baking trial | 120–140 | Harvest after planting (planted June 10–July 1, dug in October), 15 genotypes including Bonita and O’Henry |
| Louisiana plant patents (Bonita, Murasaki-29) | 90–110 | Age of the plants in a botanical description, not a harvest recommendation |
No source we found gives a minimum days-to-harvest for the US white types. As a planning figure, use the NC trial’s 120–140 days for them (our inference), and count boniato’s 150-day average only where you have a long frost-free season.
Nematodes can decide the variety. The breeders’ filings say O’Henry is susceptible to southern root-knot nematode, Bonita improves on it, and Murasaki-29 resists better than Beauregard. These are the breeders’ own statements. If you know nematodes live in your bed, start with Bonita or Murasaki-29 rather than O’Henry.
Dry doesn’t mean it keeps. Florida Extension says root decay from Rhizopus, Diplodia and Fusarium prevents long-time storage of boniato, and that boniato doesn’t keep long once harvested or cooked. For the US types, the filings report soil rot and Fusarium root rot resistance on Murasaki-29, but none of our sources gives storage life by variety. In the NC test, the roots (Bonita and O’Henry among them) were cured, then held at 57°F (14°C) and 60% humidity until the following June, but the study doesn’t report losses per variety.
| If you want… | Start with | Why | Caveat |
|---|---|---|---|
| Dry, fluffy, chestnut-like roots and have a long hot season | Boniato | Florida Extension describes it as drier and less sweet than orange types | 120–180 days; slips are hard to find; short shelf life |
| A white type for beds with root-knot nematodes | Bonita or Murasaki-29 | Breeders report better resistance than O’Henry or Beauregard | Self-reported by the breeder |
| Sweet baked roots | Pick by variety record, not color | A Japanese type baked among the sweetest; Japan’s breeding shows large variety differences | We found no published sweetness score for Bonita or Murasaki-29 on its own |
| Vitamin A from the harvest | An orange variety | White types lack β-carotene (see below) | Trade-off in texture and dry matter |
Curing White Types: Same Box, Same Rules
Cure white types the way you cure orange ones: about 10 days at 80–85°F and 85–90% relative humidity, according to Purdue Extension. The NC test cured its roots for 7 days at 81°F (27°C) and 85% humidity, so the working range among these sources is 7 to 10 days. Our 10-day sweet potato curing method walks through the box setup.
Purdue says curing converts starch to sugar and improves flavor and keeping quality. A Ugandan study of five varieties (flesh colors not reported) measured it: after eight weeks, cured roots held 47.7% total starch against 52.3% for uncured ones, while sucrose and glucose climbed during storage. Then move the roots to a dark place at 55–60°F and keep them out of the refrigerator. Purdue also notes that soil at or below 50°F can chill roots and cause internal decay in storage, so dig before the ground gets that cold.
We found no curing study that compared white types with orange ones. And because most maltose forms in the oven, not in the curing box, curing can’t supply an enzyme the variety doesn’t have.
Why Did My White Sweet Potato Taste Flat?
Most flat results trace to the variety, to skipped curing or to cold damage, and only some of those are fixable. The table pairs each symptom with its documented cause.
| What you notice | Likely cause | Evidence | What to do |
|---|---|---|---|
| Dry, chestnut-like, mild even after a long bake | It’s a boniato-type root | Florida Extension: drier, fluffier, less sweet | Cook it savory (mash, roast, soup); nothing to fix |
| Dry, bland and never turns sweet in the oven | A variety with little or no β-amylase | Null lines made under 2 mg/g maltose; two Japanese varieties steamed to only 7–9 Brix | Cooking can’t fix it; plant a different variety |
| Starchy and plain a week after digging | Not cured | Purdue: curing converts starch to sugar; cured roots had less starch than uncured | Cure 7–10 days warm and humid, then store at 55–60°F |
| Decay appears inside roots in storage | Chilling injury | Purdue: soil at or below 50°F, or refrigerator storage | Dig before cold soil; never refrigerate raw roots |
| Soft or rotting within weeks | Storage rots, especially in boniato | Florida Extension: Rhizopus, Diplodia, Fusarium; tender, bruises easily | Handle gently; eat boniato first |
| Plain after boiling or steaming | Cooking method (untested in white types) | All methods sharply cut α-amylase in a 2017 study of non-white cultivars; baking gave the biggest maltose gain in one | Bake whole, 60–75 min at 370°F; compare with a boiled root of your own |
| Poor yield in a bed with known nematode trouble | Southern root-knot nematode | Florida Extension: nematodes are a serious boniato pest; breeders’ filings: O’Henry susceptible, Bonita and Murasaki-29 more resistant | Switch variety; don’t replant the same bed with O’Henry |
What White Types Give Up: Vitamin A
White-fleshed types lack β-carotene, the pigment your body converts to vitamin A. A review of sweet potato programs in sub-Saharan Africa describes the common local varieties as “high dry matter white-fleshed types, lacking beta-carotene,” and presents orange-fleshed varieties as the plant source of it. In the Ghana panel, deeper orange also went with lower dry matter, which is the same color-versus-dry-matter trade-off. If vitamin A is why you’re growing sweet potatoes, grow orange. If flavor and texture are the point, white types earn their bed.
The Bottom Line
Choose a white sweet potato by its variety record, not its color. Bake it whole, cure it for 7–10 days, and store it at 55–60°F. If nematodes live in your bed, plant Bonita or Murasaki-29 instead of O’Henry. Treat boniato as a savory, long-season specialty crop, and grow an orange variety if vitamin A is the goal. Bake one root of any new variety before you commit a whole bed to it, because a working β-amylase, the trait that can make or break sweetness, is invisible until the oven.
Frequently Asked Questions
Are white sweet potatoes less sweet than orange ones?
Not because of their color. In a 15-variety baking test, the orange Covington and a Japanese white/cream-type were the two sweetest, and sweetness followed starch content and β-amylase activity. Boniato is the exception: Florida Extension describes it as drier and less sweet.
Is a boniato the same as a white sweet potato?
A boniato is one kind of white sweet potato. It’s the same species, Ipomoea batatas, with a bright white, very dry interior and reddish skin, and it’s often called the Cuban sweet potato. US white types like Bonita and O’Henry are tan-skinned releases from Southern breeding programs.
Can I grow white sweet potatoes the same way as orange ones?
Yes. They use the same slips, warm soil, spacing and curing. The differences are sourcing (buy certified slips), a season of about 120 days or more, nematode-prone ground (choose Bonita or Murasaki-29 over O’Henry) and boniato’s poor storage life.
Do white sweet potatoes store longer because they’re drier?
No source we found supports that. Florida Extension says root decay prevents long storage of boniato, a very dry white type. For US white types, we found no storage-life data by variety.
Are white sweet potatoes a good source of vitamin A?
No. White-fleshed types lack β-carotene, and orange-fleshed varieties are the plant source of it.
Sources
- Allan MC, Johanningsmeier SD, Nakitto M, Guambe O, Abugu M, Pecota KV, Yencho GC. Baked sweetpotato textures and sweetness: An investigation into relationships between physicochemical and cooked attributes. Food Chemistry: X 21 (2024) 101072
- Nakamura Y, Kuranouchi T, Ohara-Takada A, Masuda R, Kumagai T, Katayama K. Maltose Generation by Beta-amylase and its Relation to Eating Quality of Steamed Storage Roots of Sweet Potato Cultivars, Including Recently Developed Varieties in Japan. Japan Agricultural Research Quarterly 52(1), 7–16 (2018)
- Shin MS, Ahn SY. Textural Properties of Dry and Moist Type Sweet Potatoes. Journal of the Korean Society for Applied Biological Chemistry 30(4), 315–322 (1987) (abstract)
- Owusu-Mensah E, et al. Multi-locational assessment of some physicochemical attributes and amylase activity of sweetpotato varieties and elite materials in Ghana. 16th Triennial Symposium of the International Society for Tropical Root Crops (2012) (abstract)
- Wei S, Lu G, Cao H. Effects of cooking methods on starch and sugar composition of sweetpotato storage roots. PLoS ONE 12(8): e0182604 (2017)
- Nabubuya A, Namutebi A, Byaruhanga Y, Narvhus J, Wicklund T. Influence of development, postharvest handling, and storage conditions on the carbohydrate components of sweetpotato roots. Food Science & Nutrition 5(6), 1088–1097 (2017)
- Lerner BR. Dig Those Sweet Potatoes. Indiana Yard and Garden, Purdue Consumer Horticulture (2001)
- Stephens JM. Boniato — Ipomoea batatas (L.) Poir. UF/IFAS Extension, publication HS563 (revised 2015)
- UF/IFAS Gardening Solutions. Boniato. University of Florida Institute of Food and Agricultural Sciences
- UF/IFAS Extension. Chapter 15, Root Crop Production (beet, carrot, radish, sweetpotato/boniato). Vegetable Production Handbook, publication CV300
- Louisiana Agricultural Experiment Station. Sweetpotato plant named ‘Murasaki-29’. US Plant Patent PP19955
- Louisiana Agricultural Experiment Station. Sweetpotato plant named ‘Bonita’. US Plant Patent PP22719
- Low JW, Mwanga ROM, Andrade MI, Carey EE, Ball A-M. Tackling vitamin A deficiency with biofortified sweetpotato in sub-Saharan Africa (2017) (abstract)
