After years of research, scientists at the Norwegian Institute of Food, Fisheries and Aquaculture Research (Nofima) have concluded that chlorophyll is "probably more harmful to milk exposed to light than riboflavin."
Photosensitive riboflavin (vitamin B2), which oxidises when exposed to blue or violet light, has long been blamed for "sun light flavour" in milk - a taste Nofima compared to the "whiff of singed hair."
Nofima discovered in 2002, however, that red and orange light cause this off taste in milk as well.
“We previously though the main reason for sun light flavour was riboflavin,” Nofima scientist, Jens Petter Wold, told DairyReporter.com.
“But if this is the case, why is sun light flavour induced when milk is exposed to anything other than blue or violet light?”
Nofima delved deeper, using a method called fluorescence spectroscopy, and identified chlorophyll and degraded chlorophyll, which arrive in milk from the grass eaten by dairy cows, as the culprit.
“We started to understand that this other component was probably more harmful to milk when exposed to light than riboflavin," said Wold.
Low concentrations
While acknowledging the dairy industry "should be aware" already, Wold explained why it has taken until now to realise of the taste-damaging potential of chlorophyll in milk.
"I guess why no one has discovered it before it that the concentration of the components are very low," he said.
"When we found this, we told some dairy scientists. They laughed and said there's no chlorophyll in milk."
“It’s not good news because it shows that milk is more sensitive to light than we knew," Wold continued.
"But now we know they're there and we know they play a role in the photosensitivity of milk."
Put on the green light!
To address the issue, Wold suggested two solutions.
"The easiest way to protect the milk is to fill it in cartons that do not transmit light," he said.
"In Norway, the cardboard used for cartons is dark brown inside. That's the easiest way to protect milk."
Meanwhile, retailers stocking milk in transparent bottles should consider using only green surrounding lights, he said.
"All wavelengths of light will induce this sun light flavour," he said. "But the light that will least induce sun light flavour is green."
While Wold believes such measures are a necessity, not everyone agrees.
"In the US, most milk is in transparent containers. To me this is very strange because the shelf life is shorter," Wold said.
"I discussed this with some Americans and they said they are used to the sun light flavour."
"But to me, the flavour is terrible," he added.