20
STUDIES ON DAHI : II—GENERAL SURVEY [Vol. XXII, Part I
and uniform texture with a sweet to mildly sour taste and pleasant aroma. Only
a small percentage of the samples showed any peptonisation, gas formation or other
defect even during summer. Some of the best samples for the whole series were
obtained from Darbhanga and Brindavan (Mathura). Many of them were markedly
sweet although there was no evidence of any extraneous sugar. having been added
to them.
There is thus a considerable variation in the quality of market dahi obtained
in different centres and in some centres in different seasons of the year. The north
Indian samples as a class possessed a better texture and flavour than their south
Indian counterparts, which were generally poor in consistency and were highly
acidic in flavour. While this difference may be mainly attributed to the quality
of raw material used as well as the methods of manufacture described earlier, the
types of microflora occurring in the samples should also be considered. As a matter
of fact, the microorganisms would be responsible for the summer samples being
more acidic than the winter ones in many places and for a large number of samples
collected during the monsoon season, particularly in Bombay and in Calcutta,
showing estery or alcoholic flavours together with peptonisation, gas formation, and
other defects.
Most of the south Indian samples showed a preponderance of lactobacilli and
yeast cells over the cocci. Although streptococci were present in some of them
they must have been over-grown by the more acid tolerant and high acid producing
lactobacilli due to the nature of the starter, effect of age and temperature. This
may account for the high degree of souring in these samples. A few samples which
showed a sweeter flavour contained streptococci in greater abundance. On the
other hand, streptococci were predominant in the north Indian samples, with lacto-
bacilli and yeasts occupying a secondary place. The pleasant aroma and sweet
or mildly sour taste of these samples must be attributed primarily to them. During
summer, however, the lactobacilli were more prominent in some samples although
the majority still showed either a preponderance of cocci over rods or an equal
proportion of both cocci and rods. A few highly sour samples collected from
Calcutta and Brindavan (Mathura) contained a majority of lactobacilli, which
appeared to be different from the common types occurring in south Indian samples.
These were short rods in pairs and in chains, often developing into filaments while
the latter were long rods showing granules predominantly.
The yeasts seem to be inevitable contaminants of dahi and their greater incidence
in south Indian samples may be due to their higher acidity. Most of the yeasts
in dahi do not produce much alcohol although some are able to attack lactose as
evidenced by the presence of gas in a number of samples. They are probably res-
ponsible for bringing about peptonisation and flavour defects as well as for creating
favourable conditions for the growth of lactobacilli [Joshi and Ram Ayyar, 1936].
An appreciable number of samples obtained in Calcutta and Bombay, particularly
during the monsoon, were characterised by alcoholic and estery flavours, presum-
ably due to the action of some Saccharomyces and species of Oidia. The humid
conditions in these areas are particularly favourable for the growth of these organisms.
Of the other contaminants found in dahi, spore.forming bacteria were the most
frequent ones. A number of samples showed small rods (probably some species