can the sniff test replace ‘use by’ dates on milk?

posted on october 26, 2022   by nathan devlin

nathan devlin writes about his undergraduate research project which investigated the microbial counts of milk samples at the end of their shelf life, to determine whether a simple 'sniff test' could safely replace 'use by' dates.

what is your research about and why did you choose to study this topic?  

my research is about the microbiological status of pasteurised cow’s milk at the end of shelf life. this research is vitally important to ensure what we are consuming is safe up to the use-by date. there is currently a debate on whether to change this to a best before date. i had to select a title for my bsc food technology final year dissertation and originally chose a title about how conservative use-by dates are. i then tailored my project to focus on milk samples selected from retailers in northern ireland and tested on their use-by dates.  

what research techniques did you use? 

i focused on current literature to discover what current research has taken place and found some but limited research on this topic. to carry out the research, i used ‘pour plate’ and ‘spread plate’ techniques, focusing on total viable count (tvc) and enterobacteriaceae. i also carried out limited testing for levels of bacillus cereus and pseudomonas. i then turned my results into graphs and charts to compare shop types and milk types.  

what challenges did you face in the lab? 

i faced two major challenges which had a significant impact on my project, the budget and covid-19. as someone who loves microbiology, i love looking at the different covid-19 variants and their structures, but this pandemic struck during my testing. we hit the second wave and i had to stop testing myself and the great staff at my university carried it on. the communication was excellent so i got the results accordingly, but i would have loved to carry out all the testing myself. in terms of budget, as it was a university project, i had to budget on milk samples and testing equipment.   

what part of this research did you enjoy the most? 

the most exciting part was the results. the results were not as i expected; however, they did tally up with my literature review of worldwide studies. i expected results within the lines of specifications i was following, but the results showed that some milk samples do have high counts of viable bacteria at the end of their shelf life.  

what do you hope the future implications of your research will be? 

the research showed that it may be premature to change dating on milk. all samples when taste tested had no signs of change of aroma or taste, but when the microbiological status was studied, high microbe counts were found in some samples. i would love this project to be carried out on a large scale over a number of regions to get a better understanding. i also would love to open the debate further and fight the case for more research and argue that while controlling food waste is crucial, it’s just as important to ensure products remain safe for the consumer. my study suggests post-pasteurisation contamination was causing the concern, so i would also love further research into how this contamination has happened and what stages are contributing to this contamination.