Dahi

Dahi, Indian curd, is a well known fermented milk product consumed by large sections of the population through out the country, either as a part of the daily diet or as a refreshing beverage. In India, dahi also known as dadhi is largely made at home using traditional kitchen recipes, involving milk of buffaloes, cows and goats. Generally a mixture of cow and buffalo milk is used. Milk is boiled and cooled, inoculated with dahi starter, usually the left over from the previous day’s stock, and incubated undisturbed at ambient temperature for four to six hours until it acquires a thick consistency. Dahi is generally consumed in its original form as an accompaniment to the meal or it may be converted into raita. Dahi may be consumed as such or as sweet or savoury drink as a dessert containing sugar, spices, fruits, nuts, etc. An extensive all-India survey project on dahi revealed that there are, broadly speaking,two types of dahi prevalent in the country for direct consumption, viz. a sweet/mildly acidic variety with a pleasant flavour, and a sour variety with a sharp, acidic flavour.

i. Composition

The PFA Act deifines dahi or curd as a semi-solid product, obtained from pasteurized or boiled milk by souring (natural or otherwise), using a harmless lactic acid or other bacterial cultures. Dahi may contain additional cane sugar. It should have the same minimum percentage of fat and solids-not-fat (SNF) 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 Bureau of Indian Standards (BIS) specifications for fermented milk products are based on the type of culture used in their preparation. Mild dahi is made from mesophillic lactococci. Leuconostocs may be adjunct organisms for added buttery odour and flavour. Sour dahi contains additional cultures belonging to the thermophillic group, which are generally employed in the manufacture of yoghurt. These thermophillic organisms grow rapidly at 37-45oC, producing dahi in less than 4 hours.

Like dahi, yoghurt is a semi-solid fermented product made from a standardized milk mix by the activity of a symbiotic blend of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus cultures. For brevity we shall term the yoghurt culture organisms as ST and LB and typical dahi organisms as LL. The body and texture of yoghurt depends largely on the composition of milk employed in its manufacture. Although milk of various mammals can be used for making cultured dairy products, their industrialized production is mainly based on milk of cows and buffaloes. The composition of various milks used in the manufacture is given in Table .

                                           Composition of milk used in the preparation of cultured dairy

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ii. Classification

In a country as big as India, the consumers have different taste preferences for traditional products varying from region to region. This made the traditional products available with a varied taste. Dahi is also made in different varieties with region specific tastes. The technological developments have led to the commercialization of this pro duct. Dahi may be classified on the following basis.

•  Dahi is used for consumption, production of desi butter
•  Preparation of chakka, shrikhand and lassi.
•  Dahi is prepared from whole milk, skim milk, standard milk, and special milk.
•  Dahi is also prepared by addition of sugar and fruits.
•  Acidity of normal dahi is less than 0.7% while acidity of sour dahi is more than 0.7%.

Dahi made from buffalo milk produces a thick bodied product because of its high SNF content. It is recommended to make dahi/ yoghurt from a mix containing 11-13 percent SNF. The increased protein content in the mix results in a custard like thick consistency following the required fermentation. Higher milk solids also keep the product from wheying off. Dahi prepared from whole milk contains about fat 5- 8, protein 3.2 – 3.4 lactose 4.6 – 5.2, Ash 0.70 – 0.72, and titratable acidity 0.60 –0.80 percent.

iii. Method of Manufacture

i) Traditional method: In this method dahi is prepared at small scale, either in the consumer’s household or in the confectionary (Halwais) shop. In the household, the milk is boiled, cooled to room temperature, inoculated with 0.5 to 1.0 percent starter (previous day’s dahi or butter milk) and then incubated undisturbed for setting for about overnight. In cold weather, the dahi setting vessel is usually wrapped up with woolen cloth to maintain appropriate temperature. In the confectionary shops, the method employed for preparation of dahi is more or less same except that the milk is concentrated in a open pan before inoculation and usually dahi is set in a earthenware.

ii) Standardized method: Process on the basis of scientific lines has been developed for dahi making in the organized sector. Fresh, sweet, good quality milk is received, pre-heated and subjected to filtration and clarification. The milk is standardized to 2.5 to 3.0 percent fat and 10 percent solids not fat, pre-heated to 60oC and homogenized single-stage at a pressure of 176-kg/sq cm. The milk is heated to 85– 90oC for 15-30 minutes, cooled to 22-25oC and inoculated with 1-2 percent of specific dahi starter culture. It is then filled in suitable packaging containers of the appropriate size and incubated at 22-25oC for 16-18 hours. After proper setting of the dahi, the acidity of dahi reaches 0.6 to 0.7 percent and a firm curd is formed.The curd is cooled by circulating chilled water or air around the containers and then transferred to cold room maintained at about 4-5oC. The flow diagram for manufacture of dahi is presented here under (Fig.)

Manufacture of Dahi