Fried-food stalls reuse oil until it turns dark because testing it and selling it back are both a hassle
Thai rules cap polar compounds in frying oil at 25% of its weight, and PPTV notes the level climbs with every reuse. A Pantip commenter says stall vendors buy big bags of reused oil and fry with it openly. A would-be fried chicken shop owner asks Pantip how shops dispose of used oil, whether they can sell it, and whether a grease trap is required. Bangchak buys used oil at 20 baht a kilo, but the seller brings an ID copy and signs a slip: one Pantip reviewer got 74 baht for 3.7 kg.
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Hardware and sensors
Oil Light: a dip probe that turns red when frying oil is spent
A stall owner dips a small probe into the wok at closing. An ESP32 reads how the oil conducts electricity and lights green, yellow or red against a color chart the team calibrates on fresh, once-used and black oil. The owner stops guessing by color and smell.
Build with ESP32, 2-pin dip probe, 3 LEDs, 18650 battery
Camera and vision
Oil Card: photograph your oil on a white card and get fry-or-change
The team prints a white card with a color strip. The owner pours a spoonful of oil on it and takes a photo; Claude vision compares the oil with the strip and says keep, watch or change, and logs the batch with the date for the day's notebook.
Build with Printed color card, Claude vision, Google Sheets
Web portal
Soi Oil Run: neighbors pool used oil into one trip to the Bangchak station
Stalls in one soi list how many kilos of used oil they have. The page picks a day and one person who drives to a Bangchak 'Tod Mai Ting' station with everyone's ID copies, then splits the cash by weight so nobody loses a day over 74 baht of oil.
Build with Next.js, Google Sheets, Bangchak station list, printable weigh slip
Voice and phone
Oil Diary Line: call a number, say what you fried, hear when to change
An owner who never types calls a phone number at closing and says in Thai what was fried and how many hours the wok ran. Breaded and battered food darkens oil faster, so the voice line counts a score per batch and says 'change tomorrow' before the oil turns black.
Build with Twilio voice, Thai speech recognition, Claude, Google Sheets
Web portal
Oil Proof Sign: a printable sign that shows customers when the oil was last changed
Customers on Pantip say they can't tell which stalls fry in tired oil. The tool prints an A5 sign with a QR code; each time the owner logs a change, the page shows the date and a photo, so careful stalls earn trust instead of being lumped in with the rest.
Build with Next.js, QR generator, print-ready PDF, phone photo upload
What people reported
Oct 2026 review: sold 3.7 kg used oil to Bangchak at 20 baht/kg for 74 baht; needs ID copy and a signed slip
pantip.comMar 2026: would-be fried chicken shop owner asks how shops dispose of used oil, if they can sell it, if a grease trap is needed
pantip.comReused oil turns thick, black and smoky; polar compounds rise past the legal 25% limit with each reuse
pptvhd36.comBangchak press release: 162 stations buy used cooking oil at 20 baht/kg, price follows the vegetable oil market
thaipublica.org