We came across an article published on 25 August 2026 by Thai news outlet The Thaiger, reporting on a Facebook post that has revived debate over pesticide residue on Shine Muscat grapes.
The post was made on 24 August 2026 by a user identified as Ms Orsuda On-Khwun in the Thai consumer group “We Are Consumers”, which has over 1.3 million members. Ms Orsuda shared photographs of a bunch of Shine Muscat grapes she said she had bought on 10 July and left out of the fridge for the 43 days since. The berries were still green and still attached to their stems. The skins had wrinkled, but she said the fruit had not rotted and remained edible.
The post went viral, drawing over 10,000 reactions and over 1,000 comments. Several users concluded that fruit which refuses to spoil must have been treated with heavy doses of agricultural chemicals, with one joking that the grapes contained no preservatives, only formaldehyde. Another relayed a warning from a driver at a vineyard that pesticides sprayed while the fruit is still small can seep into the flesh and cannot be washed off.
When we conducted our research on this, we found that the detail that answers the question is the one Ms Orsuda mentions in passing – that the skins had wrinkled. Wrinkling is the signature of water loss, not of chemical preservation. Grapes are non-climacteric, meaning they do not continue ripening after harvest, and they carry a waxy outer layer that slows but does not stop moisture escaping. Left in open air, a berry steadily loses water. As it does, the sugars inside become more concentrated and the water activity of the fruit falls below the level that moulds and bacteria need to grow.
This is the same process in which raisins are made, using nothing but sun and time. A review of raisin productiondescribes dehydration as the mechanism that naturally prevents fruit from deteriorating, by lowering water activity to the point where microbial spoilage stops. A bunch of grapes left on a counter is in a race between drying out and rotting. Where conditions favour drying – low humidity, good airflow, unbroken skins, fruit that was sound to begin with – drying wins, and the result looks much like what Ms Orsuda photographed. Where a berry is bruised or punctured, or the bunch is sealed in something humid, rotting occurs instead.
On the Facebook comments attributing the grapes’ condition to pesticides, we found that insecticides and fungicides are applied to a living vine, generally weeks or months before harvest, with a mandatory waiting period – the preharvest interval – built in precisely so residues can break down before the crop is picked, as the National Pesticide Information Center explains. By the time of harvest those residues sit at the milligram-per-kilogram scale and are already falling; one field study tracking grapes as they matured measured pesticide levels declining by roughly 0.033 mg/kg for every additional day on the vine. Quantities at that scale are far too low to have any general antimicrobial effect on a whole berry.
The chemical genuinely used to stop table grapes rotting is not a pesticide at all but sulphur dioxide, applied by fumigation or slow-release pads inside the packaging, primarily to control grey mould, the fungal disease responsible for most postharvest spoilage in grapes, as a review of SO2-generating pads sets out. It works alongside cold storage, not on a kitchen table: one study found that Red Globe grapes given periodic low-dose SO2 fumigation held their quality for 240 days – eight months – under refrigeration. That is the industry mechanism behind properly refrigerated grapes lasting months, not the presence of pesticide residue.
For our readers in Singapore, the Singapore Food Agency (SFA) said on 30 October 2024 that its testing of Shine Muscat grapes had not detected pesticide residue levels of concern. Malaysia and Indonesia ran their own checks and reached broadly similar conclusions.
SFA nonetheless recommends washing, which can read as a contradiction but is not one. Its testing checks produce against maximum residue limits, and the agency is explicit that MRLs are not food safety limits but standards set with a large safety margin – fruit that passes carries residues within those limits, not none at all. Washing is the consumer’s end of a chain SFA treats as shared with government and industry, and it takes off dirt as much as residue: a 30-second rinse, a 15-minute soak and a final rinse, rubbing the surface while rinsing, and peeling where practical, since most residue sits on the skin. A 2017 University of Massachusetts study found a 15-minute soak removed surface residues of two test pesticides from apples far more effectively than plain water.
Therefore, we rate this claim as misleading. Ms Orsuda’s account of her grapes may well be accurate – fruit left in a dry, airy spot can and does shrivel rather than rot, and 43 days is not implausible. What does not follow is the conclusion drawn from it. A long shelf life at room temperature is the result of dehydration and falling water activity, not of pesticide loading, and residue levels of the kind documented in Thailand are far too low to preserve anything.
