Dahi (Curd): Intro, Classification, Composition, Nutritive Value and Uses

In this article we will discuss about:- 1. Introduction to Dahi 2. Definition of Dahi or Curd 3. Classification 4. Food and Nutritive Value 5. Composition 6. Method of Production 7. Market Quality 8. Packaging, Storage and Keeping Quality 9. Uses.

Contents:

1. Introduction to Dahi
2. Definition of Dahi or Curd
3. Classification of Dahi
4. Food and Nutritive Value of Dahi
5. Composition of Dahi
6. Method of Production of Dahi
7. Market Quality of Dahi
8. Packaging, Storage and Keeping Quality of Dahi
9. Uses of Dahi

Introduction to Dahi:

Indian curd, known as dahi, is a well-known fermented milk product consumed by large sections of the popula­tion throughout the country, either as a part of the daily diet or as & refreshing beverage. In 1966, the production of dahi was esti­mated to be about 7.8 per cent of the total milk production in India and 14.0 per cent of the milk used for the manufacture of dairy products.

Since conversion of milk into dahi is an important intermediary step in the manufacture of indigenous butter and ghee, it can be said that over 40 per cent of the total milk production in India to­day is converted into dahi.

An extensive all-India survey project on dahi was carried out nearly three decades ago. It revealed that there are, broadly speaking, two types of dahi prevalent in the country for direct consumption, viz., a sweet/mildly sour variety with a pleasant flavour, and a sour variety with a sharp, acid flavour. The micro­organisms responsible for these two types were also identified, and are maintained in selected centres as freeze-dried cultures for sale to the industry and public alike.

Definition of Dahi or Curd:

According to the PFA Rules (1976), dahi or curd is the product obtained from pasteurized or boiled milk by sour­ing, natural or otherwise, by a harmless lactic acid or other bac­terial culture. Dahi may contain additional cane sugar. It should have the same percentage of fat and solids-not-fat as the milk from which it is prepared. Where dahi or curd, other than skimmed milk dahi, is sold or offered for sale without any indication of the class of milk, the standards prescribed for dahi prepared from buffalo milk shall apply.

The Indian Standard Specifications for designation of fermented milk products based on the types of culture used are given in Table 11.11, and requirements in Table 11.12.

Classification of Dahi:

Broadly speaking, dahi may be classi­fied into two types:

I. For churning into desi (or indigenous) butter (makkhan);

II. For direct consumption.

Dahi for direct consumption may be further classified into:

(a) (i) Whole milk dahi;

(ii) Skim milk dahi.

(b) (i) Sweet (or mildly sour) dahi;

(ii) Sour dahi;

(iii) Sweetened dahi.

Food and Nutritive Value of Dahi:

It has been established that fermented milk products including dahi increase in food and nutri­tive value as compared to the original milk.

The following points are cited in their favour:

(i) Dahi is more palatable, and those who usually do not like drinking milk would consume it readily;

(ii) Dahi is more easily digested and assimilated than milk;

(iii) Dahi seems to exert a possible therapeutic value in the stomach and during intestinal disorders, due possibly to its content of antibiotics.

Composition of Dahi:

An average composition of (whole) milk dahi is given in Table 11.13.

Method of Production of Dahi:

A. For churning into desi butter (makkhan).

B. For direct consumption.

I. Sweet/Sour Dahi:

1. Traditional Method:

This invariably involves production on a small scale, either in the consumer’s household or in the sweet­meat-maker’s (halwai’s) shop in urban areas. In the household, the milk is boiled, cooled to body temperature, inoculated with 0.5-1 per cent starter (previous day’s dahi or buttermilk) and then allow­ed to set undisturbed overnight.

In cooler weather, the dahi-setting vessel is usually wrapped up with woollen cloth to maintain warmth. In the shops, the method is more or less the same except that the milk is concentrated somewhat before inoculation and the dahi is usually set in a circular earthenware mould.

2. Standardized Method:

Need:

The quality of market dahi presently sold in halwai shops in the country is generally sub-standard and variable.

The factors responsible for this are:

(i) Use of low-quality milk;

(ii) Use of unsuitable starter cultures;

(iii) Unfavourable temperatures of incubation;

(iv) Contamination from badly-cleaned utensils.

In view of the nutritional and economic importance of dahi, it has long been realized that this product should be produced on scientific lines in the organized sector of the Indian dairy industry. The conditions of production, packaging and distribution should be standardized so as to ensure the supply of an uniformly good quality product from day to day.

Technique:

Flow Diagram of Production:

Details of Production:

Fresh, sweet, good-quality milk (cow, buffalo or mixed) is received, pre-heated to 35-40°C, and subjected to filtration/clarification. It is then standardized to 2.5-3.0 per cent fat and 10 per cent solids-not-fats (in order to improve the body), pre-heated to 60°C and homogenized single-stage at a pressure of 176 kg/sq. cm.

The milk is pasteurized at 80-90°C for 15-30 minutes, cooled to 22-25°C and inoculated with 1-3 per cent of specific starter culture. It is then filled in suitable con­tainers (glass bottles/plastic cups, etc.) of the required capacity and incubated at 22-25°C for 16-18 hours, during which period the acidity reaches 0.6-0.7 per cent and a firm curd is formed. The curd is cooled to less than 12°C in about 1 hour (by circulating chilled water or air around the containers) and then stored at about 5°C in a cold room.

Note:

During overnight storage, the acidity may increase slightly.

II. Sweetened Dahi:

In the eastern region of the country, espe­cially West Bengal, a sweetened variety of dahi known as misti dahi, lal dahi or payodhi (the trade name of one particular manu­facturer in Calcutta) is quite popular. It has a characteristic brown colour, a cooked and caramelized flavour and a firm body. It is pre­pared commercially by adding 6.25 per cent cane sugar to milk (cow or mixed) either before boiling or at the time of setting.

The pronounced and intense heating causes the milk to brown and get partially concentrated. (The volume gets reduced to about three- fourths of the original.) Artificial colour, sugar-caramel and gur (jaggery) are also added during production.

After heat-treatment, the milk is cooled to room temperature and then seeded fin variable amounts) with the previous day’s product. It is usually set in earth­enware basins and the finished product obtained after 15-16 hours. The method for the production of sweet dahi has been standardized.

Note:

Studies have been made on:

(i) Utilization of colostrum for the preparation of dahi;

(ii) Development of dahi-making equipment, and

(iii) Production of new varieties of dahi.

A suggestion has also been made for a new product named dahi-kusum.

Market Quality of Dahi:

The desirable qualities in dahi offered for sale for direct consumption have been given in Table 11.14.

Note:

The effect of different salts and chemical additives on the quality of dahi has been observed. The effect of starter cultures and incubation (period and temperature) on the acidity and quality of dahi has been ascertained and the survival of pathogens in dahi investigated.

Packaging, Storage and Keeping Quality of Dahi:

The traditional container for dahi is an earthenware cup. However, modern packaging includes glass bottle and plastic/plastic-coated cup. The recommended sto­rage temperature is around 5-10°C.

Keeping Quality:

When prepared in the conventional manner, dahi has a short keeping quality at room temperature; on prolonged storage, it becomes highly acidic; this is accompanied by whey formation, making the product unfit for human consump­tion. Under refrigerated storage (5-10°C), it usually keeps well for a maximum period of one week.

Increasing Keeping Quality:

Efforts to increase the keep­ing quality of dahi at room temperatures have led to the develop­ment of a carbonated product, which has a storage life of 15-30 days without refrigeration. It is prepared as follows- good-quality milk, after heat-treatment (preferably boiling for 3-5 minutes) is cooled to 30-35°C. It is then inoculated with a starter culture @ 1 per cent and mixed well.

The culture may consist of lactic acid producers such as Str. lactis and/or Str. cremoris, together with an aroma producer such as Str. diacetilactis. The inoculated milk is filled up to the neck of each glass bottle. Now carbon dioxide gas is bubbled through the milk at 1 psi for 1 minute and the bottles are crown-corked. The milk is then incubated at 25-30°C for 16-18 hours until a firm curd is obtained.

Note:

The role of contaminating yeasts in the spoilage of dahi has been reported.

Uses of Dahi:

(a) Whole Milk Dahi:

(i) For direct consumption: either as such with salt/sugar; or as a beverage after beating the curd and mixing it with water, salt/ sugar, etc.;

(ii) For the preparation of chakka and srikhand;

(iii) For the preparation of makkhan.

(b) Skim Milk Dahi:

For direct consumption- especially by heart patients since it is low in fat, and by the low-income group of the population because it is cheap yet nutritious.