Sweet Potato — Rhodamine-B Surface-Colour Screen

What FSSAI's sweet-potato test does

FSSAI DART describes a cotton-ball screen for artificial red colour on the outer surface of sweet potato. The test can be done with cotton dampened in water and, separately, with cotton dampened in vegetable oil. If the outer colour transfers visibly to the cotton, the sample is suspicious for surface colouring.

Run the two versions separately

Do not use the same cotton ball first with water and then with oil. Use a fresh white cotton piece for each version so the observations remain independent. A separate test also avoids carrying pigment from the first rub into the second.

Gentle rubbing is enough

Rubbing too hard can damage the skin and pull natural plant material onto the cotton. Use only light pressure on a small area. Kitchen Check should show a short animation or instruction that the goal is to test the surface coating, not scrape the vegetable.

Do not say Rhodamine B is confirmed

The official rapid screen is designed to raise suspicion of colouring, but the cotton stain itself is not an instrumental identification of Rhodamine B. Kitchen Check should use the wording 'Rhodamine-B surface-colour screen suspicious' and send confirmation questions to laboratory analysis.

Appearance alone is not enough

Sweet-potato skin varies naturally from pale tan to red, purple or brown depending on variety. A bright red skin is not by itself adulteration. The relevant consumer observation is transferable surface colour in the FSSAI screen.

Do not try to wash a suspicious colour away chemically

Do not use detergent, bleach or solvents to make the vegetable look normal. If the colour screen is strongly suspicious, document the seller and batch where possible. Ordinary clean-water washing is appropriate for normal produce handling, but it is not a substitute for official investigation.

Recommended result wording

Use 'No obvious transferable red colour', 'Result unclear—repeat gently with fresh cotton', or 'Obvious red/pink colour transferred—screen suspicious'. Do not show a chemical concentration or certainty percentage.

Keep the cotton comparison visible

A useful interface can show the clean cotton beside the used cotton so the user compares the actual transfer rather than relying on memory. The app should not digitally enhance the colour or calculate a dye percentage from the photo. Lighting and camera settings can change red and pink shades. The observation remains a simple consumer screen, and any strong result should be documented without pretending that the phone camera has identified Rhodamine B.

Do not compare different sweet-potato varieties

Red, purple, tan and cream-skinned sweet potatoes are all possible natural varieties. Kitchen Check should never compare a naturally pale variety with a red variety and treat the colour difference as fraud. The cotton test is only relevant when an outer colour appears transferable. Product variety and seller information should be kept beside the screen result.