What is Butter milk ?

Buttermilk refers to a number of dairy drinks. Originally, buttermilk was the liquid left behind after churning butter out of cream. It also refers to a range of fermented milk drinks, common in warm climates (e.g., India, or the Southern USA) where fresh milk would otherwise sour quickly.   Whether traditional or cultured, the tartness of buttermilk is due to the presence of acid in the milk. The increased acidity is primarily due to lactic acid, a by-product naturally produced by lactic acid bacteria while fermenting lactose, the primary sugar found in milk. As lactic acid is produced by the bacteria, the pH of the milk decreases and casein, the primary protein in milk, precipitates causing the curdling or clabbering of milk. This process makes buttermilk thicker than plain milk. While both traditional and cultured buttermilk contain lactic acid, traditional buttermilk tends to be thinner whereas cultured buttermilk is much thicker.  Production process  The fermentation that takes place in traditional buttermilk is accomplished by controlled strains of lactic acid-producing bacteria, sparking a chemical reaction due to the environment. Traditionally, before cream was skimmed from whole milk, it was left to sit for a period of time to allow the cream and milk to separate. During this time, the milk would naturally be fermented by the lactic acid-producing bacteria in the milk. One reason this was done was to facilitate the butter churning process since fat from cream with a lower pH will coalesce more readily than that from fresh cream. The acidic environment helped prevent potentially harmful microorganisms from growing, thus the soured liquid helped increase the shelf-life of the product. Commercially available cultured buttermilk is pasteurized and homogenized (if 1% or 2% fat) milk which has been inoculated with a culture of lactic acid bacteria to simulate the naturally occurring bacteria found in the old-fashioned product. Some dairies add colored flecks of butter to cultured buttermilk to simulate the residual pieces of butter that can be left over from the churning process of traditional buttermilk. Buttermilk solids have increased in importance in the food industry.[  Such solids are used in ice cream manufacture.  Adding specific strains of bacteria to pasteurized milk has allowed for more consistent production. In the early 1900s, cultured buttermilk was once labeled as artificial buttermilk, to differentiate it from traditional buttermilk, which was also known as natural or ordinary buttermilk. This has since been obsolete, as cultured buttermilk is now considered to be natural.   Acidified buttermilk is a related product that is made by adding a food-grade acid to milk. Benefits Cultured buttermilk is lower in fat and calories than regular milk because the fat from buttermilk has already been removed to make butter. It is high in potassium, vitamin B12 and calcium. Buttermilk is more easily digestible than whole milk and it also contains more lactic acid than skim milk. Due to being more easily digestible (a result of the bacteria added to the milk), protein and calcium can be taken up more easily by the body. There are 99 kilocalories and 2.2 grams of fat in one cup of buttermilk (fat content may be different with some buttermilk brands, as some brands are made with skim milk while others are made with reduced fat milk), as opposed to whole milk that has 157 kilocalories and 8.9 grams of fat.