If you’ve ever shopped for milk, you’ve no doubt noticed what our questioner 
 has: While regular milk expires within about a week or sooner, organic milk  
lasts much longer—as long as a month.

So what is it about organic milk  that makes it stay fresh so long?

Actually, it turns out that it has  nothing to do with the milk being 
organic. All "organic" means is that the farm  the milk comes from does not use 
antibiotics to fight infections in cows or _hormones  to stimulate more milk 
production_ 
(http://www.sciam.com/article.cfm?id=milk-industry-gag-order-on-artificial-hormones-lifted) .

Organic milk lasts longer because  producers use a different process to 
preserve it. According to the Northeast  Organic Dairy Producers Alliance, the milk 
needs to stay fresh longer because  organic products often have to travel 
farther to reach store shelves since it is  not produced throughout the country.

The process that gives the milk a  longer shelf life is called ultrahigh 
temperature (UHT) processing or treatment,  in which milk is heated to 280 degrees 
Fahrenheit (138 degrees Celsius) for two  to four seconds, killing any 
_bacteria_ (http://www.sciam.com/topic.cfm?id=bacteria)  in it.  

Compare that to pasteurization, the standard preservation process. There  are 
two types of pasteurization: "low temperature, long time," in which milk is  
heated to 145 degrees F (63 degrees C) for at least 30 minutes*, or the more  
common "high temperature, short time," in which milk is heated to roughly 160  
degrees F (71 degrees C) for at least 15 seconds. 

The different  temperatures hint at why UHT-treated milk lasts longer: 
Pasteurization doesn’t  kill all bacteria in the milk, just enough so that you don't 
get a disease with  your milk mustache. UHT, on the other hand, kills 
everything. 

Retailers  typically give pasteurized milk an expiration date of four to six 
days. Ahead of  that, however, was up to six days of processing and shipping, 
so total shelf  life after pasteurization is probably up to two weeks. Milk 
that undergoes UHT  doesn’t need to be refrigerated and can sit on the shelf for 
up to six  months.

Regular milk can undergo UHT, too. The process is used for the  
room-temperature Parmalat milk found outside the refrigerator case and for most  milk sold 
in Europe. 

So why isn’t all milk produced using  UHT?

One reason is that UHT-treated milk tastes different. UHT sweetens  the 
flavor of milk by burning some of its sugars (caramelization). A lot of  Americans 
find this offensive—just as they are leery of buying nonrefrigerated  milk. 
Europeans, however, don’t seem to mind. 

UHT also destroys some of  the milk’s vitamin content—not a significant 
amount—and affects some proteins,  making it _unusable  for cheese_ 
(http://www.sciam.com/article.cfm?id=dairy-farming-old-and-new) .

There are, of course, lots of reasons people buy organic  milk. But if it's 
the long shelf life you're after, I would recommend you buy  nonorganic UHT 
milk and avoid being charged  double.



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