Concentrated milk products

Concentrated milk products

It is a very valuable products in that it consists of milk which is reduced in
bulk and given a very long keeping quality, reduction in transport and storage
costs, as well as the need to supply milk to locations where is shortage of
fresh milk.
Concentrated milks may be whole or skimmed milks which has been
concentrated by removed of apart of its water (40-50 %) with or without
addition of sugar, there are two kinds of concentrated milks (evaporated and
condensed)

Manufacture
(A) Condensed milk:
{1} Inspection of raw milk: (Total solids, fat %, sanitary and keeping
quality tests)
Milk must be of good keeping quality and of normal chemical composition.
{2} Pretreatment of milk:
Clarification, cream separation.
{3} Standardization:
The ratio of fat % to the total solids is particularly well controlled in the
production of the kind of milk (full fat or skimmed).
{4} Preheating to raw milk (Pasteurization):

By HTST (at 72 0C for 15 seconds or at 105-120 for 1-3 minutes) to destroy all pathogenic microorganisms and the higher percent of saprophytic one and also, to inactivate the milk enzymes.
{5} Addition of sugar (sucrose):
Milk is cooled to 40-50 0C then sugar is added (16-18 kg /100 kg milk).
Sugar should be obtained in a very pure condition, but it must be stored dry in order to avoid contamination with yeast and moulds, which would ferment the finished product.
Sugar is dissolved completely by thorough mixing.
{6} Evaporation or condensation or concentration:
This process performed by using vacuum pan system at which milk boils at a
temperature below the boiling point to decrease the physical and chemical changes of milk, i.e. ranges between 51-54
0C, this process continues until the content of dry matter reach to 72 %.
{7} Cooling:
Condensed milk is rapidly cooled to 30-34 0C to avoid crystallization of lactose which create a gritty taste (Sandiness) and this considered a fault in
manufacture.
Another method to avoid this fault (Sandiness) by seeding the partially cooled milk (25-30 0C) with very fine lactose crystals or lactose powder with
vigorous agitation for one hour to induce the formation of very high numbers of minute lactose crystals. (Undetectable crystals, less than 30
).
{8} Packing:
Condensed milk does not require sterilization.
The sugar content make as a preservation because it raises the osmotic pressure in milk to level at which many bacteria cannot develop, but other microorganisms especially yeast and moulds are able to develop. So, the containers used for filling should be sterilized by gas flame or stream or ultraviolet light and the air space in the can should be minimal to prevent mould growth.
(i) Vacuum method:
Cans are filled and sealed in vacuum sealing chamber by entering the uncovered cans to the vacuumed, covered and sealed or covered cans enter the vacuum chamber then pored, vacuumed and sealed.
(ii) Atmospheric method:
Cans are completely filled with milk without leaving any space inside, covered and sealed.
(B) Manufacture of Evaporated milk:
{1} Inspection of raw milk: (Total solids, fat %, sanitary and keeping quality tests)
Milk must be of good keeping quality and of normal chemical composition.
{2} Pretreatment of milk: Clarification, cream separation.
{3} Standardization:
The ratio of fat % to the total solids is must be 1:3.4 in evaporated milk and separation of fat in case of skim milk.
{4} Preheating to raw milk (Pasteurization):
By HTST (at 72 0C for 15 seconds or at 105-120 for 1-3 minutes) to destroy all pathogenic microorganisms and the higher percent of saprophytic one and also, to inactivate the milk enzymes.
{5} Homogenization by using Homogenizers: The milk is forced to pass in the homogenizing vulve in the form of spray under certain pressure rendering the fat globules small in size, loosing its ability to rise up to the surface and remaining
homogenous in the milk.

{6} Evaporation:
As in condensed milk but in case of evaporated milk 60 % of the water has been removed and the dry matter became 25 %.
{7} Cooling:
Evaporated milk is cooled at 14 0C, stabilizers as disodium phosphate or sodium citrate up to 0.1 % is added to prevent the protein precipitation during long storage of the product.
{8} Packing:
By atmospheric method and the filled and sealed cans are sterilized at 110-120 0C for 15-20 minutes, then cooled at 20 0C.
Defects (faults) of concentrated milks:
(I) Microbial defects
(1) Gassy fermentation (Gassiness or Blowing):
Gas fermentation must be sufficient in some cases to make the can bulge or even burst, the contents are mainly highly acidic, lumpy and unfit for consumption due to its bad odour and taste.
The internal surface of the affected can is usually discoloured and dark.
Causes:
{A} Certain types of coliform organisms such as Enterobacter aerogenes or Klebsiella aerogenes. Although preheating (pasteurization) destroys these organisms, it may be enter the product after pasteurization through various sources of contamination.
{b} Certain types of yeast, such as Torulopsis spherica (Torula lactis condensi) which grows well in media containing high sugar content. The yeast may survive preheating process or enter through sugar contamination or utensils contamination. In general vacuum treatment inhibits the growth of such
organisms.
{c} Certain types of anaerobes, such as Clostridium sporogenes and Cl. butyricum, which survive preheating, process and can, grow in an aerobic condition.
(2) Thickening:
Certain types of cocci or bacelli as Micrococcus ferundei or aerobic spore former e.g. Bacillus may cause this defect, they produce rennin like enzyme,
which causes aggregation of casein micelles into a three dimensional network.
Lower temperature storage and improved plant sanitation have been found helpful in combating this defect.
(3) Buttons:
Development of small reddish brown pieces of coagulated casein firm in consistency may be found on the surface of the can.
The causative organism is mould (Aspergillus repens) which, produce enzyme causing localized coagulation with disagreeable odour and taste.
(4) Rancidity:
It may be caused by the presence of high amount of lipase enzyme in milk from which the product is manufactured or the presence of lipolytic
microorganisms as yeasts and moulds.
The defect developed after 1-2 months after canning.
(II) Non- microbial defects:
(1) Grittiness: (Sandiness)

The product is gritty, instead of being normal smooth or homogenous in texture.
The fluid is characterized by the presence of large numbers of coarse crystals of sugar (lactose) due to slow cooling, which leads to formation of large (detectable) crystals of lactose.
(2) Lumpiness:
Appearance of numbers of lumps, either soft or cheesy, floating in the product.
These lumps are white in colour, mainly caused by using a milk of unusual high content of albumin and globulin (mastitic milk).
If acid flux soldering material is used in sealing of the cans, reddish lumps well developed in the product.
(3) Thickening:
Due to change in the colloidal constitution of albumin and casein, mostly due to high temperature used for preheating, condensation and storage.
(4) Brown colouration:
Condensed milk usually becomes darker in colour during storage at high temperature.
This change is exaggerated or advanced until exhibiting or involving all contents of the can.
The cause may be interaction between sucrose, lactose and milk proteins. The acidity and temperature are factors. (high temperature during processing)
Prevention of this defect is possible, if cans are stored at suitable temperature. 

You can also read Fermented milk products

 

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