September, 1950]
ABSTRACTS
221
Cleaning and Sterilization of Dairy Plants. ROWLANDS, A. (1949) J. Dairy Tech.,
2, 152-159
T HE paper deals with the importance of cleaning and sterilization of dairy
plants, methods of ascertaining the cleanliness and sterility of dairy utensils
and the choice of suitable detergents and disinfectants for the purpose.
Objective methods of evaluating cleanliness, by photoelectric measurements of
the surface film on cleaned slides, cannot be practised in the dairies where reliance
has yet to be placed wholly on visual inspection. The available methods of ascer-
taining plant sterility by themselves are not sufficient. An examination of the
first milk that passes through the plant gives valuable information about the extent of
contamination, specially when the examination is conducted on a sample aged for
24 hours at 65°F. to 72°F.
The author is of the opinion that cleaning and sterilization whether carried out
separately or simultaneously are both equally essential and indispensable. The
difficulties, arising out of the formation of hardened milk residues on dairy farm
equipments, can be best avoided by emphasizing the need for a rinse, with cold or
tepid water, immediately after the milk is removed.
A comparison of steam, hot water, hot alkalies and other chemical agents has
been made with regard to their comparative sterilizing efficiency. The suitability
of each of these, for sterilizing specific plant parts and the limitations for their
applicability, has been indicated. Steam at a temperature of 195°F./5 minutes or
170°F./15 minutes is recommended for general farm equipments and for dairy plants
where it is feasible and economical to reach the desired temperature quickly and for
the desired time. Hot water at temperatures higher than 180°F. is recommended
for immersable farm equipments and for closed systems in plants through which
water can be circulated. Use of chlorine in a concentration of 200 to 250 p.p.m.
is recommended for large storage tanks and open surfaces such as coolers open vats,
etc. For the after rinse, while employing chlorine, 10 p.p.m. of chlorine is recommend-
ed to be added to the water if its quality is suspicious. In employing alkalies
as disinfectants, such as in bottle sterilization, a minimum pH limit of 10 in the
detergent solution is considered essential. Substances such as sodium metasilicate,
trisodium phosphate and sodium hexametaphosphate are not to be used singly but
should always be used along with a basic concentration of caustic soda.
The use of quaternary ammonium compounds vis a vis hypochlorite has been
discussed. The former's suitability by virtue of its noncorrosibility, nonirritability
to the skin and freedom from undesirable odour is admitted. The limitations in
its application have, however, been indicated in presence of soaps formed in bottle
washing detergents, sodium hexametaphosphate, sodium metasilicate and water
containing over 10 p.p.m. of iron. (M.R.S.)
Deterioration on Storage of Dried Skim Milk. HENRY, KATHLEEN M., KON, S. K.,
LEA, C. H. and WHITE, J. C. D. (1948) J. Dairy Res., 15, (3) 292-363
T HE authors have carried out a detailed investigation in regard to deterioration
on storage of skim milk powder. For this purpose spray dried separated milk
powder of low (2.9 per cent), medium (4.7 per cent) and high (7.3 per cent) miosture
content, packed in air and nitrogen, was stored at 20°C. 28.5C., and 37°C. for