School of Biosciences

Milk and the 'sniff test'

Cath Rees, Professor of Microbiology in the School of Biosciences, explains the science about why you could keep milk longer than you think and help prevent unnecessary food waste.  

All food production produces greenhouse gas emissions. Wasting edible food is bad for the environment, as well as our finances. Morrisons supermarket recently announced that it will move from putting “use by” to “best before” dates on milk. It says this could potentially save seven million pints of its own-brand milk from being wasted each year. 
Milk is estimated to be the third most wasted food item in the home (after potatoes and bread) with more than 490 million pints thrown away in the UK annually.
Morrisons have advised using the “sniff test” to see if the milk is safe to use.

Prof Rees agrees this is sensible advice. If there is no detectable evidence of spoilage, the milk is safe to drink. During pasteurisation milk is heated for a short time to a high temperature. This process kills bacteria which can be present in raw milk and cause infections in humans (often called “pathogens”). Although the pathogens are killed in this process, some non-harmful microbes remain in pasteurised milk. Milk is stored in the fridge to slow the growth of these remaining microbes. Microbes will still grow, and it is the growth of these non-harmful bacteria that cause the milk to spoil. Milk may curdle and produce the “off” smell we associate with spoiled milk. However, there is no evidence the microbes growing in the milk will cause any serious harm. 

View Professor Cath Rees explaining in more detail on Notts TV interview (08/02/22)  Scroll to 7.32 on the timeline to view.

NB This advice applies only to pasteurised milk. Raw milk can still contain pathogens and should never be consumed beyond the use-by date.


Posted on Thursday 10th February 2022

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