What you see: A milky white liquid that appears on freshly cut surfaces of raw sweet potatoes.
What it is: A milky sap produced by sweet potatoes.
Eat or toss: Eat! This is normal and the sweet potato is perfectly fine.
Why do some sweet potatoes leak a white liquid when cut?
When you slice into a sweet potato, it can be a bit unsettling to see a white goo seep out. But rest assured: it’s perfectly normal. You’re seeing a type of sap that is unique to sweet potatoes.
It’s “part of the defense mechanism of a sweet potato,” Louisiana State University professor David Picha, who specializes in how produce, particularly sweet potatoes, behaves after harvest, told me. “It’s rich in chemicals that minimize the entrance of fungal and bacterial disease organisms.”
He estimated that milky sap, which is often called a “latex,” will stop flowing within a minute or so of slicing into a sweet potato. You’re much more likely to encounter these little white beads of liquid if your roots are freshly harvested. After a long time in storage, sweet potatoes are unlikely to exude the white stuff.
The “milk” that leaks from cut sweet potatoes can leave a dark stain
Eventually the milky liquid will oxidize and go dark. If sweet potatoes are injured during harvest, the defensive substance will ooze onto the scene to help protect the root, but then ultimately leave behind a black stain that you can only remove by peeling the sweet potato.
The white liquid from sweet potatoes isn’t known to trigger allergies
What’s often referred to as “sweet potato latex” shouldn’t be an issue for people with a standard latex allergy, which allergists say is triggered by certain proteins in rubber tree latex. While sweet potatoes produce a milky sap, they aren’t known to produce those allergenic proteins. (Conversely, some plants, even some that don’t produce a latex do produce similar proteins and can still cause allergic reactions. Luckily for latex allergy sufferers, sweet potatoes are not one of those plants; bananas, on the other hand, are.)
Aside from triggering allergies, some plant saps can irritate skin immediately or bind to skin proteins and cause a rash that will show up a little while after exposure. Eric Macy, a physician in the allergy department at Kaiser Permanente in San Diego, said skin irritation was theoretically possible with the sticky, white goo emerging from a sweet potato, but it wasn’t known to cause discomfort as commonly as caustic saps from other foods, such as mango.
Macy said he had never seen a patient develop contact dermatitis due to contact with a sweet potato.
Are you seeing milky white secretions from your squash, potatoes, onions or lettuce? Each scenario is different. Follow the links to learn more.
SOURCES:
- David Picha. Professor of Horticulture. Louisiana State University. Phone interview and email communication.
- Eric Macy. Physician, allergy department at Kaiser Permanente, San Diego. Phone interview and email correspondence late 2023.
- Sweetpotato Production, Processing, and Nutritional Quality. V. D. Truong (USDA‐ARS Food Science Research Unit, Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh); R. Y. Avula (Department of Food Science and Technology, University of Georgia, Athens); K. V. Pecota and , and G. C. Yencho (Department of Horticultural Science, North Carolina State University, Raleigh). Chapter from Handbook of Vegetables and Vegetable Processing, Volume II, Second Edition. Edited by Muhammad Siddiq and Mark A. Uebersax. Published 2018 by John Wiley & Sons Ltd.
- Of sweet potatoes and putting down roots. Botanist in the Kitchen. Katherine Angela Preston November 22, 2012.
