I would imagine that you'd have to have some sensors in the inside of the carton to detect the change in the pH balance of the milk. A very interesting idea.

Great idea! I think we can all relate to such an experience... I think this idea can be applied to other perishable food products as well. This will also help promote hygiene in the fridge.

I am sure there must be some chemical in sour milk that could be used for this. If the detector is able to use the gas, then it would be possible to put the detector in a reusable cap.

The pH of Milk rises as it spoils. It should not be difficult to put a litmus-style indicator strip into a carton design. Tthat makes this idea not only useful, but simply and elegantly implemented.

I was thinking about this for leftovers, where you could choose a 1-day, 3-day or 7-day sticker that would change colors as time passed. I'm not sure it's necessary for milk...can't you just look at the date on the carton and give it a sniff?

Great Idea! I've actually seen someone drink an entire quart of rotten milk -- because she was sick and lost her sense of smell.

Bright idea. But could we have different color levels between just spoiled (like yellow) to downright chunky (lime green)

Or perhaps something time-sensitive... Trader Joe's already has stickers where there is a ring that changes colors, but it's not "tapped into" the packaging in any way; it's just a sticker... Based on a time frame, it'll gradually have the outer ring a certain color, then the inside will be lighter/darker than the outside (don't remember which)fresh, then it'll blend in at a halfway point, then it's a lighter/darker color opposite the "fresh".