Acidophilus milk is milk which has been fermented with Lactobacillus acidophilus bacteria, creating a very distinctive tangy flavor and slightly thickened texture. In addition to tasting a bit different from regular milk, acidophilus milk is also believed to be beneficiary, because the bacteria can help restore the healthy balance of bacteria in the gut, promoting smooth digestion. Health food stores often carry acidophilus milk, and sometimes major markets carry it as well, especially in health-conscious communities.

The culture process used to make acidophilus milk is much like that used to make yogurt, except that acidophilus milk is not allowed to thicken as much as yogurt does. It starts with inoculation of sterile milk with the bacteria, and then allowing the milk to sit at a warm or neutral temperature so that the bacteria can thrive. The bacteria thrives in the mildly acidic environment of milk, consuming some of the lactose in the milk in the process.

Acidophilus bacteria is considered a probiotic, which means that it is an organism which is viewed as beneficial to human health in some way. Some people may have been told to eat yogurt with live active cultures for the treatment of some digestive problems and yeast infections, to take advantage of the nature acidophilus in live yogurt cultures, and acidophilus milk confers much the same benefit.

Some natural health practitioners claim that regular consumption of acidophilus milk and yogurt with live cultures can help regulate digestion and reduce the risk of yeast infections. In theory, the introduction of good acidophilus bacteria to the gut could potentially reduce the numbers of bad bacteria, which might cause problems with digestion. Some people also simply enjoy the flavor of acidophilus milk, preferring it to regular milk.

Depending on the producer, acidophilus milk may be treated to make it slightly sweet, or the tangy flavor may be retained. Some producers try to make their acidophilus milk taste as much like regular milk as possible, so that consumers can use it like regular milk in beverages and recipes, distinguishing the product from more strongly flavored cultured milk products like kefir.

Like other fermented foods, acidophilus milk should be handled with care, as it has active bacteria which can continue reproducing in the milk, changing the flavor and texture. It is a good idea to keep acidophilus milk chilled so that it does not become even tangier, and if it smells off or develops a strange color, it should be discarded.