10 STUDIES ON DAHI .—I. INTRODUCTION [ Vol. XXII, Part I
acetoin and diacetyl. Pasricha and associates [1938] examined bacteriologically
some 24 samples of bazaar dahi while Madhok and Kapoor [1942] carried out some
experiments on the preparation of dahi using pure cultures of lactic acid bacteria
singly and in combination.
From the foregoing review it is evident that dahi constitutes a highly nutri-
tious food for the people, apart from its usefulness as a refreshing drink or as a
possible therapeutic agent. It provides a satisfactory means of utilising surplus
milk economically and of preserving the food value of milk over considerable periods
under the tropical conditions prevailing in this country. Dahi is prepared in prac-
tically every cultivator's house on a cottage industry basis ; by churning it and selling
the butter or ghee made from it the cultivator earns ready cash while the by-product,
lassi, forms a palatable and nutritive drink or article of diet for the use of the family.
It is estimated that over 2,069.4 million gallons of milk or 52.4 per cent of the total
net annual production of milk in the country is converted into dahi, most of which
is utilised for manufacture of desi butter and ghee [Agricultural Marketing Adviser,
1949]. Large quantities of lassi (butter milk) are produced annually as a by-pro-
duct. The quantity of milk used for making dahi for direct consumption is estimated
at 359.1 million gallons or 9.1 per cent of the total production of milk per year. The
manufacture of dahi is, therefore, of immense economic importance both to the in-
dividual producer as well as to the dairy industry as a whole. There is also consi-
derable scope for the economic utilisation of large quantity of separated milk,
formed as a by-product in the separation of cream for butter manufacture, by con-
verting it into dahi, thus adding to the food resources of the nation.
The existing conditions of dihi manufacture in India are, however, far from
satisfactory and the quality of the product available in the market is inferior as
well as highly variable, except for a few isolated cases. Obviously, this important
branch of the dairy industry has not been properly exploited either for meeting
the nutritional needs of the people or improving the economic condition of the
producers. An additional factor to be considered in this connection is the ultimate
effect of using dahi of poor quality in ghee manufacture since the flavour and keeping
quality of ghee are said to be influenced by the quality of desi butter which in tarn
is governed by the quality of dahi [Rangappa and Banerjee, 1946].
SCOPE OF PRESENT STUDY
The above considerations are sufficient to indicate the importance of dahi
and lassi manufacture in India and the need for effecting improvements in the
existing methods of production and marketing so as to ensure a uniformly high
standard in the quality of dahi. The formulation of any step for improving the
production of dahi should, however, be based on a proper appreciation of the factors
which go to determine the quality of dahi, such as the types of organisms associated
with dahi produced in different parts of the country and their characteristics,
influence of climatic and seasonal variations, quality of milk used and method of
manufacture, about which there is very little information available. The present
study was undertaken with a view to (a) collect systematic information on the above
aspects, (b) prepare pure culture starters containing desirable organisms for the
manufacture of dahi; (c) build up technical data for guidance in the preservation