Curd and Yogurt-Dahi or curd is the Indian variety, a version of yogurt and is widely used in the daily menu of an average Indian. Several organisms are involved in the preparation of Curd which contains lactic acid. Yogurt is the preparation with the action of two organisms, Streptococcus thermophilus and Lactobacilius bulgaricus. The ideal ratio of these two organisms is 1: 1 for best results. In common usage, Curd refers to 'the domestically prepared fermented milk using a starter of the previous day' while yogurt refers to the 'industrially produced fermented milk using a particular bacteria as the starter.'