Although buttermilk originates from fresh milk just like yogurt, they are not the same thing. Buttermilk is a by-product of milk that is produced during production of butter. Buttermilk can, however, also be commercially prepared. In a commercial production setup, buttermilk is produced by pasteurization of milk by acidic compounds, that enhances the taste of the milk to a buttery flavour and give it the texture and smoothness of butter. When it comes to its nutrient value, buttermilk is fairly rich in vitamin C and vitamin A (retinol)
Yogurt, on the other hand, is produced by fermentation of milk with the help of two bacterias, Lactobacillus sp. and Streptococcus sp. There are various types of yogurts available in the market : sweetened or flavoured yogurts, containing additive sugars, fruit extracts etc. and unsweetened yogurt contains raw, unprocessed yogurt without any additives. Yogurt is known for its higher quantities of vitamin B-12.