Don't trust the best before date printed on the cap of your bottle of milk, it is only an estimate, a group of student scientists from Roscommon have warned.
It has happened to all of us - the milk has a pong despite being inside the best before date. The date however is more aspirational than actual because of the number of steps between the cow and the consumer.
"There is no accurate way to measure how long milk will last, it is just a guess," says Shane Maher who along with Thomas Cullen and James Finnerty, all 16-years-old and transition year students at CBS Roscommon, decided to look at how fresh is "fresh" milk.
“We were trying to find which was the freshest milk in our area by carrying out four different tests,” explains James.
The main one was to measure how much lactic acid was in the milk, says Thomas. Lactic acid is what makes the milk turn sour, but it is only there because of the presence of bacteria, he says.
The bacteria release an enzyme that breaks up lactose in the milk and lactic acid forms. The more acid the quicker the spoiling.
It is a challenge keeping bacterial levels low, says Shane. Milk from the cow is collected at 38 degrees and has to be cooled quickly to at least seven degrees or less.
Once pasteurised the milk is sterile but things don’t say that way for long, Thomas says.
It moves through different sets of hands, from farmer to creamery and creamery to shops and shops to consumer so there are lots of opportunities for it to warm up slightly and encourage the growth of bacteria, they say.
The only way to slow spoiling is to keep the milk at a low temperature for as long as possible.
A fridge is best obviously, but they warn against keeping the milk in the door shelves as this is the warmest part of the fridge.
They discovered that of the seven brands they tested Connacht Gold was the "freshest" on the basis of lactic acid levels.
They believe that may be because it is the milk producer closest to where they live so the milk would have spent less time in transit compared to its competitors.
