Pasteurization does effect finished product outcome. Is it homogenized? If so, I would state that could be the problem... find an un-homogenized product and see.
About 24 hours should produce a stool softening or light laxative effect... 36 hours should be neutral... or balancing... more than that could be binding... as in making cheeses and such.
Of course this also depends on the conditions... temperature, humidity, covering (lid or cloth), etc.