Re: Pasturized milk

Do you think pasturization actually kills bacteria or just puts it in a state of suspension?

Why would milk start to spoil a few weeks after purchasing the milk if the bacteria was killed with pasteurization/ in other words it seems like some of the bacteria survives pasteurization because of how fast milk can spoil(lactose fermentation) after purchasing it.

The bacteria is killed during the pasteurization.  This does not mean the milk stays sterile though.  We have bacteria all around us that contaminate many surfaces.  For example, if you take purified water that it sterile it quickly grows bacteria.  This is one of the reasons ultrapure water, such as type 1 water, has to be continually purified.  So the water picks up bacteria from the air or from the container that is exposed to the air.  The same applies to the milk jugs being filled,  the lids they put on the jugs and the nozzles that fill the jugs.  All of these are exposed to bacteria from the air.  As the milk jugs are filled the milk is once again exposed to to bacteria.

Over in Iceland, and fro what I hear Europe. they use peroxide to sterilize the milk instead of pasteurization.  The shelf life of the milk is 4 months without refrigeration.

Of course once the milk is opened its shelf life will drop as the milk is exposed to higher levels of bacteria.  And as any traces of peroxide finish decomposing the milk is again more prone to more bacterial overgrowth.