Pastuer discovered that heating beer and wine was enough to kill most of the bacteria that caused spoilage, preventing these drinks to turn sour. The process achieves this by eliminating pathogenic microbes and lowering microbial numbers to prolong the quality and the shelve life of the beverage. The process is widely used today in the diary industry and other food processing industries to prolong the shelve life of foods and also for food safety
Pasteurization enables a can or bottle of beer to be stored at room temperature for up to 120 days and beyond. Draft beer that has not been pasteurized has a shelve life of about 45 to 60 days. Draft beers that are not pasteurized often have a life of 6 to 9 months.
Contents of a non-pasteurized keg that has been used at special outdoor events, and stored outside during the event should not be served once the event has ended.
Pasteurized kegs can be returned to the the cooler, and it's content can be served or consumed at later time.
Unpasteurized beer on the other contain most of the micro-organism and noble yeast left over from the brewing process. They tend to have a short shelve life as compared to pasteurized beers and should be mostly keep in it's cooler to preserve taste and quality.
It's highly not recommended to re-consume an unpasteurized beer that has been left open (whether bottled or canned) for a while.
Impact on Beer Flavour - Does pasteurization has an impact on the taste of beer? This is a question that has long been debated and, is truly based on personal preference.
Do you like to eat your veggies cooked or raw? Some people might argue that raw vegetables have the best taste and best attributes such as the crispiness, freshness whereas other might argue that cooking the vegetables releases more flavour in the vegetable
The choice is mostly tuned to personal taste.
If you'd like to read more about the differences, you can check out this article on ''Pasteurized and Unpasteurized Juice'' from the Michigan State University's website