QUALITY OF WATER USED IN DAIRY PROCESSING
The water received in the dairy shall be primarily fresh and of potable in nature. The drinking water supplied to a dairy in its original or treated state shall be suitable for human consumption without causing any health risks and shall be without any objections in taste, odour and appearance.
Fresh water that has been used in heat exchange circuits for cooling purposes and has absorbed heat can be used as warm water, e.g. for cleaning purposes. Warm water is fresh water coming off from cooling installations. Quality requirements depend on the utilization, whether water is used in production (as cooling water, water for cleaning, boiler feed water) or for social services (bathrooms, kitchens). Water used in a dairy must meet microbiological standards, so that germs do not have any effect on the manufacturing processes or on products. It must be free of inorganic or organic sediments and must be colourless.
Certain requirements regarding temperature and chemical composition must also be met; organoleptic quality must be in line with that of drinking water.
Water for production purposes
This includes water that is in direct contact with or incorporated in milk or milk products. Examples are water for the production of long shelf life products, for the manufacture of lactose, butter wash water, water for cheese production and water as a solvent for product preparations. This water must meet drinking water quality standards.
The standards for drinking water quality are shown in the following Table.
S.No |
Criterion |
Unit |
Guideline |
Maximum tolerance |
1 |
pH |
|
6.8-8.6 |
≥6 and ≤ 9 |
2 |
Temperature |
°C |
8-12 |
≥ 3 and Not more than ≤20 |
3 |
Chloride ions |
mg/l |
≤250 |
350 |
4 |
KMnO4 |
mg/l |
≤12 |
20 |
5 |
Potassium ions |
mg/l |
≤10 |
10 |
6 |
Fluoride ions |
mg/l |
1.0 |
1.3 |
7 |
Calcium ions |
mg/l |
≤ 100 |
280 |
8 |
Sodium ions |
mg/l |
≤ 80 |
150 |
9 |
Total hardness |
° |
2 - 25 |
40 |
10 |
Carbonate hardness |
° |
2 - 25 |
25 |
11 |
Oxygen, dissolved oxygen O |
mg/l |
610 |
≥ 4 and ≤ 14 |
12 |
Carbon dioxide |
mg/l |
0.4 |
|
13 |
Dry matter |
mg/l |
1000 |
1500 |
14 |
Iron, total |
Mg/l |
≤ 0.1 |
0.3 |
15 |
Mesophilic microorganisms |
per ml |
< 5 |
20 |
16 |
Psychrophilic microorganisms |
per ml |
< 50 |
100 |
17 |
Coliform bacteria |
|
absent in 100 ml |
absent in 100 ml |
18 |
Pathogenic bacteria |
|
absence |
absence |
Cooling water
Cooling water, that is used directly for cooling of milk and milk products must meet drinking water quality standards but can be used later as warm water for cleaning processes or in heat recovery circuits. However when surface water that does not meet drinking water standards is used for cooling purposes, it must be discharged as wastewater.
A special requirement for cooling water is that the hydrogen carbonate hardness should not exceed 6° (German hardness); otherwise sediments and incrustations can form on the walls of the equipment and inside the pipelines. If cooling water is recirculated for heat recovery in open cooling installations, another aspect to be considered is that the original components in the water are concentrated by evaporation and are deposited on the heat exchanger surfaces.
Quality standards for drinking water used for manufacturing processes in dairies
Water for cleaning purposes
Water used for cleaning of machines, installations, pipelines and storage tanks must also meet drinking water quality standards. If permitted by the authorities, used water can be utilized for cleaning purposes if
a) The original quality has been drinking water.
b) It has been used only in closed circuits.
c) Storage tanks for used water are closed.
d) Used water from storage tanks has been chlorinated.
The objective is to utilize used water for all cleaning purposes in order to reduce fresh water consumption and to recover energy. For cleaning premises and streets, other types of water can be used.
Boiler feed water
There are no hygienic requirements for water that is used in the manufacture of steam in boilers. An exception is the manufacture of "culinary steam". In the UHT processing of milk, the steam produced is called culinary steam and for its production, the water quality standards must be equivalent to the drinking water. Boiler feed water does not have to meet the standards for nitrate and chloride content. However, carbonate and sulfate hardness must be very low.
Hardness in water is generally caused by dissolved calcium, magnesium and iron salts (especially hydrogen carbonates and sulfates). Total hardness of water is composed of temporary or carbonate hardness and permanent or sulfate hardness, which is due to calcium and magnesium sulfate. It is possible to remove carbonate hardness by boiling.
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