TRADITIONAL DAIRY PRODUCTS

Lesson 24. MISTI DAHI PREPARATION, QUALITY, PACKAGING AND SHELF LIFE, DEFECTS

Module 7. Fermented dairy products

Lesson 24
MISTI DAHI PREPARATION, QUALITY, PACKAGING AND SHELF LIFE, DEFECTS

24.1 Introduction

Misti dahi is also known as Misti doi, Payodhi and Lal dahi. It is a traditional sweetened fermented milk product popular in the eastern part of India, notably West Bengal, Bihar and Assam. It is prepared by lactic acid fermentation of sweetened milk. Misti dahi is regarded as a special dessert on ceremonial occasions both in the rural and urban Bengal. The product is commonly available in earthen pots of different sizes. A good misti dahi has a characteristic brown colour, firm consistency, smooth texture and caramelized flavour.

Buffalo milk is preferred for the preparation of Misti dahi due to high fat content, which induce a rich creamy product with excellent mouth feel. The high protein content of buffalo milk leads to the formation of firm coagulum which resists whey separation during storage and transportation.

24.2 Traditional Method of Misti Dahi Preparation

Traditionally, it is prepared by Halwais on a small scale to meet the local demand. Whole cow milk or buffalo milk or their combination is added with sugar (upto15% of the milk) and it is heated continuously in an open pan at a simmering temperature of 68-70°C for 6-7 hours or boiled to reduce the volume to 60-70% of the original. Intense heating imparts cooked flavour and brownish colour to the product. Artificial colour, caramel sugar and/or jaggery are also added based on the consumer preference. The mix is then cooled to about 40°C and inoculated with the previous day’s product. It is then filled into earthen pots of consumer size or bulk size vessels and incubated overnight at room temperature. After firm setting of curd, it is shifted to a cooler place or stored under refrigeration temperature.

The conditions, under which the product is generally prepared, stored and marketed by the halwais are unhygienic. The product is sometimes contaminated with different types of microorganisms including yeasts and moulds which gain entry into the product from utensils and surroundings. Many flavour defects such as fruity, alcohol, highly acidic and flat and textural defects such as gassiness, weak body, wheying off and thick crust on top surface are observed in most of the market samples. These defects may be due to difference in quality of milk, degree of concentration of milk solids, type of culture used, incubation time, processing conditions and temperature of storage.
In view of the growing demand, a technology for industrial production of this product has been standardized.

24.3 Industrial Method of Production

In the organized sector a wide range of milk products are used for sourcing milk solids for the production of misti dahi. Extreme care is needed in the selection and use of the raw materials and sweeteners. The ingredients should be fresh, good in microbial and sensory quality.

Calculated amount of milk and cream is taken into a multipurpose vat. Skim milk powder is added through a venturi assembly to increase the level of total solids and sugar is added at the rate of 9 – 10%. Commercially available Caramel is added normally at the rate of 0.10 to 0.12%. After the mix is prepared, it is heated to 90°C for 10 min in a vat or plate pasteurizer. Then the product is cooled to 40 – 42°C and starter culture containing Lactococcus lactis subsp. lactis and Lactococcus lactis var. diacetilactis is added at the rate of 1% to the mix and mixed well. Selection of appropriate type of starter culture is very important and crucial as it affects the flavour, consistency and acidity development in the presence of sugar and caramel. After inoculation the product is packed into sanitized polystyrene cups and sealed airtight. The sealed cups are incubated at 40 – 42°C for about 6 to 8 hours till the acidity develops to about 0.8 % lactic acid.

Once the product develops the desired acidity level of 0.8% lactic acid, it is shifted from incubation room to cold store and maintained at < 5°C. Care should be taken to maintain the temperature of the cold store, so that product doesn’t freeze.

*Homogenization can be omitted where consumer look for malai on the top of misti dahi

Fig. 24.1 Flow diagram for production of misti dahi

Sugar controls the acid production of misti dahi because of its effects on osmotic pressure and improves its acceptability. Sugar helps in carmalization and development of brown color which is desirable, product should be stored at 5°C or below. Higher temperature of storage can lead to defects like whey separation and bitterness. Very low temperature induces ice-crystals formation which damages the texture.

Table 24.1 Chemical composition of misti dahi

24.5 Shelf Life

Due of high acidity (0.8%) and high sugar level misti dahi has a shelf life of about 12 days at 4°C and 2days at 30°C. The shelf life mainly depends on post manufacture contamination particularly with yeast and moulds. Hence attempt should be made not to unduly expose the finished product to atmospheric contamination.

24.6 Packaging

Misti dahi is packed in food grade polystyrene and polypropylene cups in 100g, 200g pack sizes. Various packaging machines of upto 400 cups/min speed are available to package cultured dairy products in different sizes. The packaged product should be stored at <5°C for extended shelf life.

24.7 Factors Affecting the Quality Misti Dahi

24.7.1 Level of fat

With the increase in the fat percentage there is a decrease in acid development and increase in flavour volatile due to stimulation of the culture to produce more flavour volatiles specially acetoin. Misti dahi prepared with low fat content produces a firm curd with higher curd tension.

24.7.2 Homogenization pressure

The flavour volatiles increase with the increase in homogenization pressure due to availability of substrate material, consequent to homogenization which may stimulate the flavour production activity of starter culture. In unhomogenised misti dahi, there is fat separation and the product lacks in smooth creamy taste.

24.7.3 Level of milk solids not fat (MSNF)

The average initial acidity of milk increases with the increase in MSNF content and the rate of acid development lowers with increase in MSNF content. The increased osmotic pressure (Due to increase in soluble constituents e.g. lactose and salts from higher level of MSNF) in milk slows down the acid development by the culture bacteria. There is reduction in amount of flavour volatiles due to high MSNF which is dependent on pH. The firmness of misti dahi increases with the increase in MSNF content. The increased concentration of casein improves the water binding capacity the curd.

24.7.4 Level of cane sugar

At higher sugar levels there is a reduction in water activity which inhibits the growth of starter bacteria. Thus diminishing acid and flavour production. The production of diacetyl and acetyl methyl carbinol decreases with increase in sugar level. The curd tension of misti dahi is lowered with the increase in sugar level. The higher sugar concentration leading to lower acid development and correspondingly with higher pH will prevents formation of a firm gel.

24.7.5 Defects in Misti dahi

Fruity flavor, alcoholic, acidic and flat flavor are the common flavor defects normally found in market samples of Misti dahi. Common textural defects include gassiness, weak body, whey off and soggy body. By following standard manufacturing protocol and maintaining chemical standard these defects could be controlled.

References

Aneja, R.P., Mathur, B.N., Chandan, R.C. and Banerjee, A.K. 2002. Technology of Indian Milk Products. A dairy India Publication, Delhi, India
Kanawjia, S.K., 2006. Developments in the manufacture of lassi. In: Developments in Traditional Dairy Products, lecture compendium of the 21st short course. CAS in Dairy Technology, NDRI, Karnal. Pp: 55-63
Ghosh, Jayanta and Rajorhhia 1990.Misti Dahi. Indian.J. Dairy Sci. Page No. 239