A: Beneficial bacteria basically predigest milk for us, making it much easier for our digestive tracts to absorb the nutrients in milk. When bacteria are introduced to warm milk, they do what any other living thing does: feed, multiply, and produce by-products. The bacteria feed on milk sugar (lactose), converting it to lactic acid and thereby making milk accessible to those who have difficulty digesting lactose. Lactic acid helps break down milk proteins and other nutrients, making them easier to process. Lactic acid also has an astringent preservative effect on the body after consumption.