Lassi

Lassi (stirred dahi) is a ready-to-serve fermented milk beverage popular in India particularly in summer months. Good quality lassi should have creamy consistency,smooth texture, glossy sheen and white colour with yellowish tinge. Mild acidic flavour and sweetish taste of lassi make it a refreshing soft drink. It is flavoured either with salt or sugar and other condiments or spices like ginger, coriander, and mint, depending on regional preferences. Lassi is obtained from pasteurized whole milk or partly skim milk, cultured with lactic and aroma/flavour producing organisms.In many parts of the country products, like butter milk, chhach, mattha obtained after churning of sweet cream, or whole milk dahi and removal of butter are termed as lassi and usually consumed in salted or spiced form. Also a product prepared from cultured skim milk, commonly known as cultured butter milk is classified as lassi.

i. Chemical Composition

Lassi is a white to creamy-white viscous liquid with a sweetish, rich aroma and pleasant mild acidic taste. The chemical composition of lassi depends on the type of milk, initial composition of milk, level of concentration of milk solids and the sugar level. The proximate composition of lassi is given in table. 

Proximate composition of lassi

ii. Manufacture of Lassi

Production of lassi has been confined, to a large extent, to the households and local halwais mainly because of non-availability of a standardized technique for the manufacture of uniform quality lassi and its limited shelf life. In 1972 the technology was standardized at NDRI, Karnal and regular production of lassi started. The method of manufacture of lassi involves standardization, heating and cooling of milk to inoculation temperature, addition of starter culture and setting of milk. Sugar @ 12-15% of milk dissolved in equal quantity of water is added in the form of a syrup which has been pasteurized and cooled separately. Smooth consistency of lassi is obtained by homogenization of the mix. Flavour is added before packaging. In general, the quality of milk, starter culture and the method of manufacture influence the quality of lassi. Chemical quality of milk is important for desired body and texture and consistency and to meet the legal requirements, if any. But the more important effect of chemical and bacteriological quality of raw milk is on the growth of starter organisms. Therefore, the milk, which serves as a growth medium for the microorganisms must be of high microbial quality and free from mastitis milk, lipolytic rancidity, residual antibiotics and germicides. There should not be any bacteriophage contamination.

Pooled milk is considered to be the most suitable for the manufacture of fermented milk products, like, yoghurt, dahi, shrikhand etc. A suitable heat treatment is applied to milk to make it free form most of the vegetative cell of microorganisms associated with raw milk. However, some spore formers and stable enzymes remain unaffected by the commonly employed heat treatment in the manufacture of fermented milks.

The basic role of starter culture is to bring about acid coagulation of milk and impart characteristic flavour. The culture must be pure, active and free from gas producing microorganisms. Presence of more than one type of lactose fermenting microorganisms in the starter culture is required for the production of diacetyl flavor in dahi. A lactic culture comprising of Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris and Lactococcus lactis subsp. diacetilactis is used for dahi for lassi making. Setting of milk is terminated at an acidity of 0.70 – 0.80 per cent LA. To the set curd sugar syrup is added which requires sufficient heat treatment (80-90oC) to prevent microbial contamination through sugar. It is also essential to cool the syrup to room temperature before addition to dahi to prevent hardening of fine curd particles and whey separation. Homogenization prevents cluster formation, rising of fat to the surface and improves consistency.

In a typical method of manufacture of lassi, standardized milk (4% fat) is heated to 90oC for 10 min and cooled to 25oC before addition of starter culture (1%). Cultured milk is incubated for 12-16 hr at 25-28oC, the set curd is broken by stirring and sugar syrup is mixed. The mixture is homogenized and packaged after the addition of flavour. On an average the product contains 3 per cent fat., 6-7 per cent SNF and 10-11 per cent sugar. The acidity ranges from 0.6 to 0.7% LA. Flow chart for mechanized production of lass is depicted in Fig.

Flow diagram for manufacture of lassi

iii. Technical Developments

Lassi keeps good only for a day or two at room temperature. Under refrigeration,the keeping quality of lassi is extended considerably. Further extension of shelf life is achieved by UHT processing after fermentation and packaging aseptically. Wheying off may occur but it can be avoided by using a suitable stabilizer and proper processing conditions.

UHT Lassi: Significant advancements have been made towards the industrial production of lassi through application of UHT. Standardized milk (9-10% SNF and 0.5-1.0% milk fat) is warmed to 85oC for 30 minutes or 91oC for 2.5 to 5 minutes and cultured with suitable lactic culture (dahi culture at 31oC). It is then fermented at 22oC to lower its pH to 4.5. Set curd is broken with the help of a stirrer while sugar solution (30% in water) is added to give 8-12 percent sugar concentration in the blend. Lassi is then homogenized at 13.7 Kpa (2000 psi) and UHT processed at 135-145oC for 1-5 seconds and packaged aseptically employing standard equipment.

Directly acidified milk beverage: The addition of organic acids such as acetic, fumaric, lactic, tartaric, citric, and phosphoric acid to milk result in the formation of a coagulum at pH less than 4.6. Employing this principle a method for the manufacture of long life directly acidified milk beverage has been developed at NDRI, Karnal.Toned milk is diluted with water in the ratio of 7:3, preheated to 45oC and additives like sugar (18%), carboxyl methyl cellulose (0.8%), trisodium citrate (0.09%) are added and mixed. The milk is pasteurized at 70-75oC and cooled to 6-8oC. The pH of milk is then adjusted to 3.75 with the addition of diluted phosphoric acid (2.25 N) followed by heating to 65oC, addition of colour and homogenization. The homogenized mix is cooled to room temperature prior to addition of flavour and bottling, the filled bottles are finally sterilized at 110oC for 5 min, cooled and stored.The beverage has a shelf life of 120 days at 5oC and 75 days at 30oC.

Lassi Powder: In order to meet the seasonal and regional requirements of lassi, a technology has been developed for the manufacture of lassi powder, which upon reconstitution yields lassi like beverage. The method involves concentration of skim milk by reverse osmosis process, standardization of the concentration with cream to contain 10 per cent fat and 30 per cent total milk solids, inoculation with starter culture and setting of curd. The curd is broken by agitation to obtain a smooth slurry which is subsequently spray dried under predetermined conditions. Sugar is  blended. The powder on reconstitution with water yields lassi-like beverage.Acceptability of the beverage could be enhanced by fortification with fruit juices.The lassi powder was found to contain moisture 5 per cent, fat 29-31 per cent and protein 23-34 per cent.