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Studies in the Transport of Milk in Warm Condition
(iii) Storage of processed milk at room temperature
(80°-90°F.) and low temperature (48º-50ºF:) for
20 hours in small aluminium cans.
(iv) Storage of processed milk in bulk at a fluc-
tuating storage temperature (130°-150°F.) for eight
hours in large tinned steel milk cans.
PLAN OF WORK
Required quantities of raw, mixed milk as detailed
under different sections were collected and heated
to 150ºF. and retained at that temperature for 30
minutes in a specially constructed milk pasteur-
izing can, provided with a stirrer, a tight-fitting
lid and an arrangement for inserting the thermometer
to record the temperature of the milk without
opening the lid. This can was inserted in a bigger
vessel containing water which was directly put
over a charcoal fire. The milk while being heated
was stirred at five minutes intervals to attain uniform
temperature. After the process of heating and
retaining the milk at the temperature was comple-
ted, it was immediately distributed in containers,
which were previously sterilized. After filling the
containers, they were closed with tight-fitting
lids. Those samples which were to be maintained
at an elevated temperature were at once transferred
to a hot chamber maintained at 150°F. and the sam-
ples were immediately cooled down to between
48º-50ºF. by immersing the containers in cold brine
solution and then transferred to cold storage
(48º-50ºF.).
Section I
Eight pounds of milk were taken, heated, re-
tained at the temperature and then distributed in
glass milk bottles as detailed above. These were
stored at 150ºF. and 48º-50ºF. for the total period
of eight hours.
Section II
In this section the experimental treatment to the
milk was the same as described above, the modi-
fications being (i) the use of 12 lb. of milk (ii) the
use of aluminium milk cans of 5 lb. capacity as
containers and (iii) the storing of milk for a total
period of 16 hours,
Section III
To study the behaviour on processed milk, held
at room temperature (80°-90°F.) versus that held
in cold storage (48º-50ºF.), this part of the work
was done. The modification made was the holding
of one lot of milk, after heating and retaining at
150°F. for half an hour, at room temperature while
holding the other lot of samples, after cooling,
at cold storage temperature (48º-50ºF.).
Section IV
These trials were made to study the effect of high
storage temperature, within a certain fluctuating
limit, which may be obtainable under field conditions
on a large quantity of milk.
Sixty pounds of milk were employed for the
trials. The method of heating followed here was
slightly different. The whole milk can was immersed
in hot water and the milk heated to 150°F. and held
at that temperature for half an hour. After com-
pletion the can was removed and transferred to
an insulated chamber which was heated by a char-
coal fire. The inside temperature was not cons-
tant but fluctuated between 130° and 150°F.
In every case the following chemical, bacterio-
logical and physical tests were applied to milk
samples, drawn at various stages:
Chemical
1. Fat per cent
2. Acidity (lactic
acid per cent)
Bacteriological
1. Total No. of
organisms per c.c.
of milk
2. Presence of B.
coli in milk.
3. Methylene blue
reduction test
4. Fermentation
test
Physical
(only applied to
milk after hot
storage)
1. Smell
2. Taste.
The milk samples were drawn and examined at
the following stages:
(i) Raw milk (before treatment).
(ii) Milk heated to 150°F. and held at that
temperature for 30 minutes.
(iii) Milk after complete storage period at both
the storage temperatures, i.e. 150°F. and 50ºF
(iv) Milk samples drawn at three and six hourly
intervals in the case of trials under section III.
RESULTS AND DISCUSSION
Results of the chemical analysis of various samples
are given in Table I, while the data on bacterio-
logical examination are given in Tables II
and III.
From the chemical results it will be observed
that the fat percentage in milk was not altered by
the two different treatments, namely storage at