Before I met Dominic, eight years ago, I had no idea how the lighting in food displays and retail stores can REALLY affect the milk you buy. Light oxidizes the milk in plastic gallon containers that are exposed to direct lighting. This light exposure not only affects the taste of said milk, it also can affect the nutrient content of it.
My buying tip: if you purchase milk at a grocery store like the one in the photo, always dig to the very back, darkest shelf area of the milk display to pick out your milk for purchase.
I have been asked by a store employee, one time, why I was digging to the back for my milk and of course I told him the reason why; that I didn't want to buy oxidized milk. It's amazing the difference in taste, my kids will even notice the taste of even the slightest oxidation, it's very apparent. Now, if you buy milk in cartons, it will be safe from light oxidation and if you happen to buy milk at Costco, where it's sold in plastic containers but boxed in cardboard, it's also safe from oxidation.
A study conducted by Milk Quality Improvement Program (MQIP) scientists at Cornell University, Ithaca, N.Y. measured the amount of time it took to get noticeable flavor changes. Here's what they found:
'Reduced fat (2%) milk in high-density polyethylene (HDPE) containers were exposed to lighting similar to the retail dairy case (2000 lux), where the average light exposure is 8 hours. The study was conducted from 1999 to 2001. The conclusions? Half of the teen and adult consumers could detect an off-flavor with less than 2 hours of light exposure. Also, the teens were asked how much they liked the milk'. They thought that the light-oxidized milk was objectionable. The longer the milk was exposed to light, the less they liked the milk.'