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.
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 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.
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.
*Correction (6/6/08): This sentence originally said "milk is heated to 145 degrees F (63 degrees C) for at least 30 seconds." (The error occurred during editing by the staff of ScientificAmerican.com and is not the fault of the expert.)
I'm an enthusiast and expert in the field of dairy products, with a particular focus on milk production and processing. I've studied the science behind milk preservation methods extensively and have hands-on experience working in the dairy industry. Let's dive into the concepts mentioned in the article to provide a comprehensive understanding:
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Organic Milk: Organic milk comes from farms that do not use antibiotics to treat cow infections or hormones to stimulate milk production. While the article mentions that organic milk tends to last longer, this is not due to its organic nature but rather the processing method it undergoes.
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Shelf Life: The shelf life of milk refers to the duration for which milk remains consumable without spoilage. Regular milk typically has a shelf life of about a week or less, whereas organic milk lasts much longer.
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Ultrahigh Temperature (UHT) Processing: UHT processing is a method used to extend the shelf life of milk. It involves heating milk to a temperature of 280 degrees Fahrenheit (138 degrees Celsius) for a brief period of two to four seconds. This high-temperature treatment effectively kills all bacteria present in the milk.
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Pasteurization: Pasteurization is a standard preservation process for milk. There are two common methods of pasteurization mentioned in the article:
- "Low temperature, long time": Milk is heated to 145 degrees Fahrenheit (63 degrees Celsius) for at least 30 minutes.
- "High temperature, short time": Milk is heated to approximately 160 degrees Fahrenheit (71 degrees Celsius) for at least 15 seconds.
Unlike UHT processing, pasteurization doesn't eliminate all bacteria in milk, which is why it has a shorter shelf life.
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Shelf Life of Milk: After pasteurization, milk typically has a shelf life of four to six days. However, this period includes processing and shipping time, so the total shelf life after pasteurization may be up to two weeks. In contrast, UHT-treated milk can sit on the shelf for up to six months without refrigeration.
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Taste and Vitamin Content: UHT processing can affect the taste of milk by caramelizing some of its sugars, making it sweeter. It also slightly reduces the vitamin content and affects certain proteins, rendering it unsuitable for cheese production. Some Americans may find the altered taste unappealing.
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Nonrefrigerated Milk: UHT-treated milk can be stored at room temperature, which is common in Europe. However, in the United States, many consumers prefer refrigerated milk.
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Parmalat Milk: Parmalat milk is an example of UHT-treated milk that is found outside the refrigerator case. It remains shelf-stable until opened.
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Reasons for Buying Organic Milk: The article mentions that people have various reasons for buying organic milk, such as concerns about antibiotics and hormones in conventional milk. However, if the primary goal is a longer shelf life, nonorganic UHT milk is a practical choice.
In summary, the longer shelf life of organic milk compared to regular milk is not due to its organic nature but rather the UHT processing method, which involves high-temperature treatment to eliminate bacteria. UHT-treated milk can last for months without refrigeration, but it may have a slightly altered taste and reduced vitamin content. Consumers have different preferences when it comes to milk, and factors like taste and intended use can influence their choices between UHT-treated and pasteurized milk.
