Does reduced-fat milk last longer than whole milk? If so, why?

Scientists are still looking into this, but skim milk tends to last a few days longer than regular milk because some bacteria develop more slowly in skim milk, said Cornell University dairy researcher Steven Murphy. According to Murphy, fat itself doesn’t speed deterioration of milk, but perhaps, one theory goes,  bacteria spores migrate to fat. Whatever the reason, food scientist Susan Brewer claims that fat does, in fact, cause almost all dairy products to deteriorate.  The unsaturated fatty acids break down into compounds which have rancid, cardboard, sweaty odors.
 
Source(s):
Steven C. Murphy, Senior Extension Associate (Milk Quality Improvement Program)
Department of Food Science, Cornell University
Susan Brewer, Ph.D.  University of Illinois, Department of  Food Science and Human Nutrition