I will not claim to be the expert in the dairy processing department, so I have reached out to find some answers. First, let's break down a few definitions...
Pasteurization - discovered by Dr. Louis Pasteur in 1862. While looking for a solution to prevent wine and beer from souring, Dr. Pasteur demonstrated that by heating the beverages to boiling and then allowing them to cool, the microbes responsible for souring the beverages were destroyed. Pasteurization is the process of heating liquids or foods to kill disease-causing microorganisms and to increase shelf life. Commonly found pasteurized products include: fruit juices, beer, milk, ice cream and non-carbonated beverages.
Low-Temp Pasteurization - also known as "Vat Pasteurized" or "Low Temp, Long Time" - refers to milk being pasteurized at a low temperature for a long time. LTLT milk is heated to 63*C (145*F) for 30 minutes. This method can result in a "cooked" flavor in fluid milk.
LTLT is the primary form of pasteurization in processed dairy foods, including starter cultures for cheese, yogurt, buttermilk and some ice cream mixes.
High-Temp Pasteurization - "Traditional Pasteurization" or "High Temp, Short Time" (HTST) - milk is heated to a minimum of 72*C (161*F) for 15 seconds (sources ranged from 161*F to 165*F, for 15 seconds). This is the most common pasteurization method used in the United States. The process involves metal plates and hot water to heat the milk, followed by rapid cooling.
Side note: A similar process is used to Cool milk on our farm. Milk fresh from the cow is hot, as her normal body temperature ranging between 101.5-103*F. The milk passes through a Plate Cooler, metal plates with ice cold water rolling through on one side and the hot milk on the other. The rolling motion of the liquids maximizes contact on the metal and cools the milk instantly before it arrives in the bulk storage tank to await transportation to the milk plant.
Ultra High-Temp Pasteurization (UHT) - milk is heated to 138*C (280*F) for 2 seconds and packaged in sterile, air tight containers. UHT milk is considered 'sterile' and does not need to be refrigerated and has a shelf-life of up to 90 days, however it does need to be refrigerated once the container has been opened. UHT is commonly used by the Armed Forces as a mandatory supplement, and in countries where refrigeration is unavailable or expensive. It is gaining popularity in the US due to the extended shelf-life and the increasing variety of container size.
The larger issue at hand here, is the claim that pasteurization reduces the nutritional value of milk. This claim is FALSE. While Pasteurization does kill the bacteria found in milk that can cause disease and does break down some of the components of milk, the actual nutritional value is the not effected. While the enzymes, or milk proteins, may break down during pasteurization, they are not destroyed. Your body breaks the enzymes down even further during the course of digestion.
This graphic is an excellent depiction of the effects of HTST and UHT Pasteurization on milk, compared to Raw Milk. I tried to make the graphic appear larger, with no such luck. Click on the image to see it in larger view.
As noted by this graph, only a few vitamins are effected by pasteurization, and the largest effect is about a 3% reduction in Ascorbic Acid, also known as Vitamin C. The last time I checked, milk wasn't readily consumed as a source of Vitamin C. And typically the orange juice I purchase in the store is also pasteurized.
On our farm, we have installed a pasteurizer to pasteurize milk that we feed our baby calves. This ensures that the live enzymes in the raw milk do not have the opportunity to make our calves sick, another step we take to maintain their overall health and nutrition.
Another note on the graphic above suggests that pasteurization makes "milk difficult to digest." Typically, milk digestion issues are correlated to lactose intolerance. Lactose is a natural sugar found in raw milk, that is NOT effected by the process of pasteurization. Lactose intolerance is the inability of your body to digest the "milk sugar", commonly as the result of a deficiency of lactase, an enzyme produced by the lining of your small intestine. A body unable to digest lactose does not constitute a milk allergy, which can have symptoms similar to other allergic reactions.
Lactose Free Milk is an option for those who like dairy, but have an intolerance to lactose. Lactase, is added to convert the lactose into glucose and galactose, thus making it easier to digest. Lactose free milk can be found in the dairy case of grocery stores.
Yes, raw milk can be and is consumed in many areas. However, handling and food-safety are absolutely critical when it comes to handling raw milk. Immediate refrigeration, constant and accurate temperature control, and shelf-life restrictions are all things to take into consideration. Be sure to check the raw milk distribution laws and licensed distributors in your area before making a purchase. You can also find more information at RealRawMilkFacts.com. If the health benefits of milk are what you're after, rest assured that you're getting the same nutrients in pasteurized milk, Organic or not.
I hope that this helps explain the process of pasteurization and the minimal effect it has on the nutritional value of your milk. I enjoy the opportunity to answer questions about dairy farming or the surrounding industry and am happy to do my best to answer your questions!