Must lactose-free milk be ultra-pasteurized? In this question I asked why lactose-free milk lasted such a long time. The answer was because it is ultra-pasteurized. This leads naturally to another question: does lactose-free milk have to be ultra-pasteurized?My initial guess is that it does because:Since the lactase added to make the product lactose free breaks down lactose into twice as many sugar molecules, any living bacteria have twice as much nutrients to thrive in.Since the disaccharide lactose has been broken down into the simple monosaccharides glucose and galactose, the bacteria do not need to produce their own lactase to use the sugar; thus any non-lactase producing bacteria can thrive in the milk.And finally, I have been adding lactase to regularly pasteurized milk to produce my own lactose-free milk. However, this milk almost always goes bad a couple of days before the Best-By date stamped on the container.This all leads me to think that lactose-free milk must be ultra-pasteurized in order for it to have any reasonable shelf life.
You can now buy (at least in Switzerland where I live) lactose-free milk which is not ultra high-temperature pasteurized. They are kept chilled in the supermarket alongside "normal" milk. So I would say based on this, no lactose free milk does not have to be ultra pasteurized. Though I will note, they hardly tasted sweet at all and they are quite expensive, nearly double the price of ordinary milk.