“Can you sniff this?” is rarely a promising conversation starter at the best of times, but when it’s right before you thrust a questionable bottle of milk under someone’s nose, it’s borderline criminal. 

We imagine this was the final workplace gripe in the UNSW tea room before things got technical, and now we, the public, will reap the benefits. Researchers at the UNSW School of Computer Science and Engineering have been hard at work developing a smartphone app that can detect if your milk is fresh or destined for the dump.

The app has been developed in a bid to reduce food waste (and ease tensions in the break room), citing UN data that around 20 percent of dairy products are wasted globally each year. 

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So how does this noseless piece of tech actually administer the sniff test? It’s all about the vibe of the thing. The app, called VibMilk, captures vibration signals created by your smartphone’s motor and its built-in inertial measurement unit (IMU) – the part that orients you in maps, balances your spirit level, etc. 

When milk spoils, its density changes as bacteria growth increases lactate levels and decreases glucose levels. The uniform consistency of fresh milk will split into water, curds and whey as bacteria levels rise. Using VibMilk, your phone can detect these changes in density and viscosity without even having to open the bottle. VibMilk takes those vibration readings and then analyses them against known spoiling pH levels of milk. Science!

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Can you drink milk after its use-by date?

Team lead, Professor Wen Hu notes that use-by dates are an educated guess as to when milk will actually spoil.

“The ‘use-by’ date represents an indication rather than a definitive expiration,” he says. “When manufacturers set these dates, they make assumptions about factors like temperature and storage duration based on worst-case scenarios.”

Fridge temperature, where in the fridge you store your milk and bacteria potentially introduced after opening can all affect the accuracy of the use-by label. 

Of course, the types of packaging that the milk is stored in will impact the vibration readings, so the team is now testing the app against various packaging materials used by milk manufacturers. Stay tuned, and in the meantime, bring air freshener.

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