Skim Versus Whole Milk: Which Spoils Faster?

Some food safety charts claim that whole milk goes off more quickly than skim milk, but the scientific evidence is mixed. Learn more about milk science in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
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

(00:24):
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

(00:46):
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

(01:07):
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

(01:27):
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.

(01:51):
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

(02:13):
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

(02:35):
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.

(02:57):
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,

(03:21):
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

(03:43):
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,

(04:04):
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.