Lactose-free milks are the same as regular milk, except for the addition of lactase.
Regular milk contains the milk sugar lactase, while lactose-free milk does not. Lactase, an enzyme produced by the stomach, breaks down the milk sugar galactose so you can absorb it. People who have lactose intolerance, a lactase deficiency, have gastrointestinal symptoms when they consume dairy products containing lactose. Commercial milk producers add lactase to lactose-free milk so that you can drink it without experiencing gastrointestinal symptoms. Lactase makes the milk taste sweeter. To render the lactase enzyme inactive, manufacturers ultra-pasteurize the milk, which can change the consistency and taste. Ultra-pasteurization also extends the shelf life.
Lactose-free milk tastes sweeter than regular milk because the milk sugar lactase is broken down into two simple sugars, galactose and glucose. Simple sugars taste sweeter on your tongue than complex sugars. A Kansas State University study published in the June 2009 issue of "LWT Food Science and Technology" on the characteristics of lactose-free milk reported that the sweeter, more highly processed, cooked taste of lactose-free milk might be a deterrent to consumer interest in the product.
Ultra-pasteurized milk has a longer shelf life than regular milk, lasting up to 60 days compared with between seven and 16 days for regular milk, according to Strauss Family Creamery. This is a benefit for the manufacturer because lactose-free milk doesn't have as rapid a turnover on the store shelves, since there isn't as high a demand for it as for regular milk. Producers heat the milk to at least 280 degree Fahrenheit for at least two seconds. Regular pasteurized milk is heated to 170 degrees Fahrenheit for 19 seconds and then immediately cooled to 40 degree Fahrenheit or lower.