Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, I'm Lauren vogel Bomb, and we've all had moments of uncertainty and, let's face it, paranoia about the state of the food sitting in our refrigerators. You might be able to eyeball some of the suspicious items, check for expiration dates on others, and with some milk maybe you'll probably
take a quick whiff and hope for the best. But if you've ever looked a shelf life chart to figure out how long your milk might last, you might have noticed that skim milk is said to last a day or two longer than whole milk. But is that really true and if so, why? Before we really get started, I should state that there is by no means universal agreement on this issue. Some dairy scientists say skim milk lasts longer because certain fat loving microbes can't develop as
quickly in non fat milk. Others say that whole milk lasts longer because free fatty acids might actually be natural preservatives. Still, others say that maybe there isn't a difference in spoilage at all, it's just that we notice flavor changes more in one or the other. There's only been one major controlled study on the spoilage rates of whole and skim milk, and it was somewhat inconclusive. Skim milk was found to spoil slightly faster, but the researchers weren't exactly sure why.
Bacteria that are psychotrophic, that is, cold resistant, are what caused spoilage in the fridge, and in the study, they multiplied at the same rate in both types of milk. When the milk spoiled, both whole and skim contained similar strains of bacteria. There was a pronounced difference and how whole and skim milk reacted when they were injected with the same spoilage microorganisms, but they affected the milks taste and smell more than they did the actual spoilage rate.
Whole milk, for the record, tended to turn sour and skim milk was on the bitter side. So for the purposes of your average milk consumer, there's really no hard and fast rule about which kind will spoil faster. If whole milk does last longer than skim, the difference is so slight that any given gallon of skim milk could
outlast any given gallon of whole milk. The spoilage rate depends on so many variables manufacturer production methods, milk formulation, plant sanitation, storage temperatures, pH level, moisture content, just to name a few. A small change in just one of them could give any particular container of milk a slightly longer shelf life than another. A couple other factors make things even more ambiguous. For one, it's pretty much impossible
to pinpoint the exact moment of spoilage. Depending on your sense of smell and taste and your tolerance for changes in milk flavor, you might turn up your nose at a gallon of milk that someone else might readily swig. And there's no federal regulation of milk expiration dates in the United States. Only twenty states legally standardized the date that's printed on the bottle, and those standards vary widely.
One state might mandate a cell by date of a certain number of days after pasteurization, whereas milk jugs and another state would be printed with a use by date. The upshot don't base your milk purchases on which type might last longer. If you're concerned about shelf life. You'd be better off following a few simple steps to slow down milk spoilage, whether you're a whole or skim drinker. First,
make sure your refrigerator is the correct temperature. It should be set at forty degrees fahrenheit that's four point four degrees celsius. Store your milk on an interior shelf instead of on the door, which fluctuates more in temperature. And make sure you put your milk back in the fridge as soon as possible after using it. Leaving it out on the counter for even a few minutes exposes it to light and heat, giving bacteria a chance to spring
into action. Today's episode was written by Alison Cooper and produced by Tyler Clang. Bonus fact for the episode, the origin of milks expiration date labels and of expiration date labels in general in the United States rests with a campaign started by al Capone. To learn more about that,
check out an episode of my other podcast, Saber. The episode is called expiration Dates Best if listened by and of course, for more on this and lots of other fresh topics, visit our home planet pastuff works dot com.