December, 1950]
ABSTRACTS
287
Milk Condensing. W. P. CROCKER (1950). J. Soc. Dairy Tech. 3, (2) 110-114
T HE author has given a review containing the latest imformations about the
manufacture of the two forms of condensed milks viz., the sweetened variety
and the unsweetened or evaporated one. For sweetened condensed milk the manu-
facturing cycle comprises of (a) the preheating of the raw milk, (b) the addition of
sugar (c) the condensing of the sweetened mixture and (d) the cooling of the condensed
milk. The purpose of preheating is to kill the pathogenic and other undesirable
organisms, and to inactivate those enzymes causing spoilage of the condensed milk.
As a relatively severe preheating has a stabilizing effect (which reduces the tendency
of the condensed milk to thicken progressively after manufacture), in the present
commercial practice the preheating process may range from 180ºF. with a long holding
time, to momentary heating to 212ºF. (or even higher) according to circumstances.
The same is carried out in continuous units—either by the familiar plate pasteurizer
or the tubular type. The addition of sugar, which exerts a preservative action,
may preferably be done by mixing boiled and filtered sugar-syrup with the milk
in the condensing pan through a separate line. The condensing is carried out in a
vacuum pan. The cooling of the condensed milk has to be slow in order to prevent
crystallization of the lactose into larger crystals. The same is carried out by cir-
culating the milk through tubes surrounded on the outside by cold water. When
the condensed milk attains normal temperature it is filled into its final containers.
With the unsweetened condensed or evaporated milk the cycle of operations is
(a) preheating, (b) condensing, (c) homogenization and (d) sterlization. In the pre-
heating, the milk is raised at least to the boiling point. For the condensing, special
continuous double effect (or even triple effect) pans are now coming into general
use, which save about 40 per cent of the steam necessary to operate coil pans used
before. The condensed milk is homogenized before cooling, with the purpose of
securing a stable emulsion. The evaporated milk is then filled into tins which are
subjected to complete sterilization by heating to a temperature of 240ºF. for 15
minutes. Immediately afterwards the tins are cooled by means of water.
Both the full-cream sweetened and unsweetened condensed milks must have at
least 31 per cent of total milk solids, including 9 per cent of fat in the final product.
The variable composition of the initial raw milk has, therefore, to be counteracted
by standardization before condensing in order to give a constant ratio of fat to non-
fatty solids in the condensed milks. Also the proportion of the added sugar in the
percentage composition of sweetened condensed milks is not a fixed amount, but
must be related to the water-content of the product.
In the manufacturing precautions to be observed are included good quality raw
milk, adequate preheating treatment, avoiding all sorts of metallic and bacterial
contamination and good air-tight sealing of the condensed milk tins, in order to secure
a first-class product of requisite keeping quality. (S.D.)
Factors Affecting the Keeping Quality of Ghee. D. P. PERSAI AND C. R. BARNICOAT
(1949), J. Dairy Res., 356-362
I N this paper, the effect of (a) nature of the starter, (b) method of manufacture,
and (c) heating conditions on the keeping properties of ghee made from cow
butterfat are described. Keeping qualities were assessed from the times required by