Introduction to Cold Culturing and Fermentation
Fermentation is one of the oldest and simplest methods used to preserve milk and enhance its nutritional properties. In humid climates, the acidic flavor imparted by fermentation is highly desirable. Fermentation also improves digestibility and introduces functional health benefits absent in raw milk.
Fermented dairy products like curd (dahi) are essential across many cultures. Ancient Indian Vedic literature references various types of cultured dairy products, such as:
- Prasadjya: Diluted, churned dahi with suspended butter grains
- Payasya: A mix of strained curd, boiled milk, crystallized sugar, and herbs
- Shrikarini: Dahi blended with sugar and spices
Product Description: What is Dahi?
Dahi, or curd, is a semi-solid fermented milk product produced using lactic acid bacteria (LAB) as starter cultures. These bacteria consume lactose to produce lactic acid, carbon dioxide, and volatile flavor compounds like diacetyl—key to the signature flavor of dahi.
A balanced mix of acid- and flavor-producing bacteria helps develop dahi with a firm body and pleasant texture, critical for large-scale dairy manufacturing.
Definition of Curd (Dahi)
Dahi is made by souring pasteurized or boiled milk with LAB or related microorganisms. It can optionally include cane sugar and must meet the minimum fat and solids-not-fat (SNF) levels of the milk it’s derived from.
Note: If sold without specifying the type of milk, the buffalo milk standard for Dahi applies, unless explicitly labeled as skimmed milk dahi.
Methods of Dahi Preparation
4.1 Traditional Method
- Boil milk for 5–10 minutes
- Cool to room temperature
- Add buttermilk or previous day's curd
- Let it set overnight undisturbed
In halwai shops, milk is condensed to raise solid content, particularly proteins, resulting in custard-like curd that doesn’t whey-off easily.
4.2 Industrial Method of Dahi Manufacturing
4.2.1 Raw Material Selection
High-quality milk that meets microbiological, physical, and chemical standards is essential.
4.2.2 Filtration & Clarification
Raw milk is preheated to 35–40°C and filtered to remove foreign matter.
4.2.3 Standardization
- Fat: 0.5% (adjustable)
- SNF: 11–13% using skim milk powder (SMP) or condensed skim milk
- Increased SNF improves curd texture, protein, and calcium content
4.2.4 Homogenization
- Performed at 60°C, pressure: 175 kg/cm²
- Reduces cream separation
- Enhances smooth texture
4.2.5 Heat Treatment
Milk is treated at 90°C for 10 minutes to:
- Denature proteins for viscosity
- Kill contaminating microorganisms
- De-aerate for better bacterial growth
- Improve nutritional environment for starter cultures
4.2.6 Packaging & Fermentation
- Cool milk to 37°C, add 1–1.5% starter culture
- Use food-grade polystyrene or polypropylene cups
- Incubate at 37–42°C till pH reaches 4.4–4.5
- Then, rapidly chill to <5°C
Packaging sizes: 100g, 200g, 400g
Machines with speeds up to 400 cups/minute are used for efficient packaging.
4.2.7 Storage
Store finished curd at 4–5°C in clean, hygienic environments to avoid contamination.
Conclusion
This article explored cold culturing in curd, detailing both traditional and industrial production methods. Curd production is a vital part of food processing consultancy, offering opportunities for process optimization, plant automation, and value-added product development.
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