Sour curd, commonly referred to as plain yogurt, is a versatile dairy product that plays a significant role in various cuisines around the world. It is made by fermenting milk with lactic acid bacteria, specifically Lactobacillus bulgaricus and Streptococcus thermophilus, which convert lactose into lactic acid. This process gives the curd its distinctive tangy flavor and thick, creamy texture.

The preparation of sour curd begins with heating milk to a specific temperature to kill any unwanted bacteria. The milk is then cooled to a suitable temperature for fermentation, at which point a starter culture containing live bacteria is added. The milk is kept at a warm temperature for several hours to allow the bacteria to ferment the lactose, resulting in a thickened, tangy curd.

Sour curd is a staple in many culinary traditions. In Indian cuisine, it is used in a variety of dishes such as raita, lassi, and kadhi, and is also enjoyed on its own or with rice. In Mediterranean and Middle Eastern cuisines, it is a key ingredient in dips like tzatziki and is often served with grilled meats and vegetables. In Western cuisine, plain yogurt is commonly consumed as a breakfast item, often paired with fruits, honey, or granola, and used in baking and cooking to add moisture and a tangy flavor to dishes.

Nutritionally, sour curd is rich in protein, calcium, vitamins B6 and B12, riboflavin, potassium, and magnesium. It is also a natural source of probiotics, which are beneficial bacteria that support gut health, boost the immune system, and aid in digestion. The fermentation process also makes yogurt easier to digest than milk, making it a suitable option for those with lactose intolerance.

The tangy taste of sour curd can vary depending on the fermentation time and the type of milk used. Longer fermentation results in a more pronounced sourness, while using full-fat milk produces a richer, creamier texture. Homemade sour curd allows for control over the flavor and consistency, tailored to personal preferences.