Why Organic Milk Lasts Longer than Regular Milk - The difference lies NOT in the source of the milk but in how it's processed.
LTLT Pasteurization - The pasteurization process commonly used with regular milk is called "low temperature, long time" (LTLT) pasteurization, which heats the milk to 145 degree F for at least 30 minutes. The temperatures used in LTLT pasteurization do NOT kill all the bacteria in the milk, but do kill enough to keep it safe for a week or so.
UHT Pasteurization - The pasteurization process commonly used with organic milk is called ultrahigh-temperature pasteurization (UHT) and heats the milk to 280 degrees F for 2-4 seconds. UHT pasteurization kills all bacteria in the milk.
Why not use UHT for Regular Milk? Besides killing all bacteria, UHT pasteurization destroys some of milk's vitamins (a small amount) and alters some proteins in the milk so that it cannot be used for making cheese.