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Cold Culturing in Curd – A Food Technology Insight

Q: What standardization targets should we set for fat and SNF in industrial dahi production?

For industrial dahi manufacturing, milk is typically standardized to 0.5% fat (adjustable to the product) and 11–13% SNF, with solids-not-fat raised using skim milk powder (SMP) or condensed skim milk. Increasing SNF improves curd texture and raises the protein and calcium content of the finished dahi, which supports a firmer body and reduces the tendency to whey off.

Q: What homogenization and heat treatment conditions are used for curd milk?

In dahi manufacturing, homogenization is performed at 60°C at a pressure of 175 kg/cm², which reduces cream separation and gives a smoother texture. Heat treatment follows at 90°C for 10 minutes to denature proteins for viscosity, kill contaminating microorganisms, de-aerate the milk for better bacterial growth, and create a better nutritional environment for the starter cultures.

Q: At what temperature and pH do we incubate and then stop fermentation for dahi?

After heat treatment, the milk is cooled to 37°C and inoculated with 1–1.5% starter culture. Incubation is carried out at 37–42°C until the pH reaches 4.4–4.5, at which point the product is rapidly chilled to below 5°C to arrest fermentation. Finished curd is then stored at 4–5°C in clean, hygienic conditions to prevent contamination.

Q: Which packaging materials, cup sizes and filling speeds are used for curd?

Industrial dahi is filled into food-grade polystyrene or polypropylene cups, with common pack sizes of 100 g, 200 g and 400 g. Because incubation happens in the pack, filling occurs before fermentation, immediately after inoculating milk at 37°C with 1–1.5% starter culture. Cup filling machines with speeds up to 400 cups per minute are used for efficient packaging at scale.

Q: How does the traditional halwai method differ from the industrial process, and why does that curd not whey off?

The traditional method boils milk for 5–10 minutes, cools it to room temperature, adds buttermilk or the previous day's curd, and lets it set overnight undisturbed. In halwai shops, the milk is condensed to raise solids content, particularly proteins, producing a custard-like curd that does not whey off easily. The industrial route achieves similar body by standardizing SNF to 11–13% instead.

Q: Which milk standard applies if our dahi label does not state the type of milk used?

Dahi is defined as pasteurized or boiled milk soured with lactic acid bacteria or related microorganisms, optionally containing cane sugar, and it must meet the minimum fat and solids-not-fat levels of the milk from which it is made. If dahi is sold without specifying the type of milk, the buffalo milk standard applies, unless the product is explicitly labelled as skimmed milk dahi.

By PMG Engineering · 19 Nov 2024

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.

Frequently asked

What standardization targets should we set for fat and SNF in industrial dahi production?

For industrial dahi manufacturing, milk is typically standardized to 0.5% fat (adjustable to the product) and 11–13% SNF, with solids-not-fat raised using skim milk powder (SMP) or condensed skim milk. Increasing SNF improves curd texture and raises the protein and calcium content of the finished dahi, which supports a firmer body and reduces the tendency to whey off.

What homogenization and heat treatment conditions are used for curd milk?

In dahi manufacturing, homogenization is performed at 60°C at a pressure of 175 kg/cm², which reduces cream separation and gives a smoother texture. Heat treatment follows at 90°C for 10 minutes to denature proteins for viscosity, kill contaminating microorganisms, de-aerate the milk for better bacterial growth, and create a better nutritional environment for the starter cultures.

At what temperature and pH do we incubate and then stop fermentation for dahi?

After heat treatment, the milk is cooled to 37°C and inoculated with 1–1.5% starter culture. Incubation is carried out at 37–42°C until the pH reaches 4.4–4.5, at which point the product is rapidly chilled to below 5°C to arrest fermentation. Finished curd is then stored at 4–5°C in clean, hygienic conditions to prevent contamination.

Which packaging materials, cup sizes and filling speeds are used for curd?

Industrial dahi is filled into food-grade polystyrene or polypropylene cups, with common pack sizes of 100 g, 200 g and 400 g. Because incubation happens in the pack, filling occurs before fermentation, immediately after inoculating milk at 37°C with 1–1.5% starter culture. Cup filling machines with speeds up to 400 cups per minute are used for efficient packaging at scale.

How does the traditional halwai method differ from the industrial process, and why does that curd not whey off?

The traditional method boils milk for 5–10 minutes, cools it to room temperature, adds buttermilk or the previous day's curd, and lets it set overnight undisturbed. In halwai shops, the milk is condensed to raise solids content, particularly proteins, producing a custard-like curd that does not whey off easily. The industrial route achieves similar body by standardizing SNF to 11–13% instead.

Which milk standard applies if our dahi label does not state the type of milk used?

Dahi is defined as pasteurized or boiled milk soured with lactic acid bacteria or related microorganisms, optionally containing cane sugar, and it must meet the minimum fat and solids-not-fat levels of the milk from which it is made. If dahi is sold without specifying the type of milk, the buffalo milk standard applies, unless the product is explicitly labelled as skimmed milk dahi.

CITE THIS

PMG Engineering. (2024). Cold Culturing in Curd – A Food Technology Insight. PMG Engineering. https://pmg.engineering/Article/383/cold-culturing-in-curd-a-food-technology-insight/

https://pmg.engineering/Article/383/cold-culturing-in-curd-a-food-technology-insight/