Here is a list of Important machineries used in dairy industry: 1. Milking Machine 2. Heater 3. Pasteurizer 4. Bottle Filling Unit 5. Bottle Capping Unit 6. Bottle and Can Washing Unit 7. Cream Separator 8. Refrigerator.
1. Milking Machine:
Milking machine is used for milking of milch cattle.
The machine consists of:
(a) Vacuum pump
(b) Teat cups
(c) Pulsator
(d) Claw
(e) Tubes and
(f) Bucket
Principle of Working:
Milking is done with the help of electric motor or a small engine. The vacuum pump produces a suction which is transmitted by a pipe line to the milking units. This suction is continuous. The teat cups are double walled units with metal bodies and rubber linings.
A device called Pulsator connects alternately the space between the metal walls and the rubber lining, first with the atmosphere and then with the suction. When the space between the Liners and the metal walls is connected to the atmosphere, the liner collapses, squeezing the teat. The vacuum level inside the liner is momentarily reduced. The intermittent squeezing and release is essential to machine milking.
(a) Vacuum Pump:
It is a pump used for sucking air from the vacuum reservoir and pushing it out to atmosphere. Vacuum pump may be rotary type or reciprocating type. It creates a pressure of about half of the atmospheric pressure i.e. about 0.5 kg per sq cm. To check the excessive vacuum, a vacuum regulator or a relief valve is provided in the pipe line. A vacuum gauge is also fitted in the line to show the degree of vacuum created in the line.
(b) Teat Cup:
It is a cup like thing which sucks the milk from the teat of the cows or buffaloes. The cups are double walled with metal bodies and rubber linings. The space between the metal walls and the rubber lining is alternately connected first with atmosphere and then with the suction side.
(c) Pulsator:
It is an air valve which alternately connects the space between the metal walls and the liners of the teats, first with the atmosphere and then with the suction side. Usually it is driven by the vacuum itself, operating alternately on two diaphragms or on the two ends of a piston. The pulsation varies between 45 to 55 per minute.
(d) Claw:
It connects the teat cups to the vacuum and milk lines. The milk is separated from vacuum by claw bowl. It provides a vacuum reservoir which helps to stabilize the vacuum at the teats.
(e) Tubes:
Suitable tubes are provided for transferring milk from the teats to the reservoir.
(f) Buckets:
Usually stainless steel buckets are used for storage of milk. Buckets of different size and shapes are available for use.
2. Heater:
Milk is required to be heated or cooled for conditioning purpose. Devices used for heating and tooling the milk is called Heat exchanger.
It is divided into four classes:
i. Internal tube type
ii. Barrel type
iii. Plate type
iv. Surface type
i. Internal Tube Type:
Two tubes of different diameters are placed horizontally, one after other. The number of tubes may vary between 8 and 24. The internal tube carries the milk and external tube carries steam or boiling water. With both liquid moving in tubes, lying side by side, heat is transferred from one to another.
ii. Barrel Type:
It consists of a barrel and tubes. Tubes are usually made of stainless steel. Steam or boiling water flows through the barrel. The tubes containing milk pass through the barrels. The barrel is provided with an inlet and outlet for the heating and cooling medium. Pumping arrangement is there to pump milk through the tubes.
iii. Plate Type:
It consists of corrugated steel sheets or plates which are arranged in vertical position. Sheets are separated with the help of gaskets. Milk and heating medium pass in alternate spaces. It is used for large size dairy. The sheets or plates are sealed at the edges with gasket and are clamped tightly within a press. The channels and ridges of the corrugations increase the effective area of the heat exchange. The heat transfer efficiency of this system is as high as 70 to 80%.
iv. Surface Type:
There are small diameter horizontal tubes in rows, carrying the heating medium. A thin stream of milk flows down under gravity over the outside portion of tubes. Suitable troughs are there on the top of the tubes for distributing the milk. There is collecting trough at the bottom also.
3. Pasteurizer:
Pasteurization is defined as heating the milk up to specified temperature for a predetermined duration of time for removing bacteria and harmful organism from the milk.
Pasteurization is mainly done in one of the following ways:
(a) Heating the milk up to 61°C and holding it at that temperature for 30 minutes.
(b) Heating the milk up to at least 71°C and holding it at that temperature for at least 15 seconds.
The followings are the main types of pasteurizers commonly used:
i. Batch type
ii. High temperature short time (HTST)
iii. Vacreators
i. Batch Type:
Small quantity of milk is handled by batch type pasteurizer. Milk is heated to 61°C for 30 minutes. It consists generally of a cylindrical tank of about 500 litres capacity. Hot water is circulated or sprayed through a jacket all-round the milk except at the top. For heating the milk uniformly, a mechanical agitator is also provided for agitation of milk.
ii. High Temperature Short Time (HTST) Pasteurizer:
HTST pasteurizer is such that milk is heated to 71°C and is maintained at that temperature for at least 15 seconds. A similar pasteurizer known as Ultra high temperature short time is also used at some places in which milk is heated to 135°C temperature and kept at that temperature for only two seconds. Usually plate type heat exchanger is used.
HTST pasteurizer mainly consists of:
(а) Regeneration unit
(b) Heater
(c) Filler
(d) Holding pipe
(e) Flow diversion valve
(f) Cooler.
Regeneration is the method of using the heat of pasteurized milk to warm up cold raw milk. The regenerator unit consists of a couple of tubes, one carrying raw milk and other carrying pasteurized milk which is to be cooled. The cold raw milk is warmed by the hot pasteurized milk, flowing in the opposite direction. In regenerating unit, the cold milk is heated from 5°C to about 55°C. After the milk is heated, it is pumped to the plate where it is heated to 71°C. There after the milk is sent through a tube. The milk takes about 15 seconds to travel through it.
There is a flow diversion valve at the end of the holding tube. If the milk is not at the proper temperature of 71°C, the flow diversion valve automatically diverts back the raw milk to the supply tank. Hot pasteurized milk is cooled from 70°C to 18°C by the incoming raw milk at 5°C. From there the pasteurized milk flows directly into the cooling section where it is cooled to 4°C. It is kept there in proper bottle for consumption purpose. Usually ice water or brine is circulated in the cooling section.
In flow diagram it can be seen that raw milk is stored in the storage tank, from where it goes to a balance tank. The pump sucks the milk from balance tank and sends it to regenerating unit. From regenerating unit, milk passes through a number of items in regular sequence. It goes to filter and then to cooler through the regenerating unit. Finally it reaches the bottling unit.
Comparison between HTST Pasteurizer and Batch Type Pasteurizer:
HTST Pasteurizer:
a. Low initial cost.
b. Space requirement is less.
c. No possibility of milk getting spoiled due to delay in pasteurization.
d. Automatic cleaning of the plant can be done easily.
e. Capacity can be increased by increasing the plates for heat exchange.
Batch Type Pasteurizer:
a. High initial cost.
b. Space requirement is comparatively more.
c. Some possibility of getting the milk spoiled due to delay in pasteurization.
d. Cleaning of the pasteurizer is not very easy.
e. Capacity is almost fixed.
iii. Vacreators:
It is used for butter, cream and other similar products. It consists of three vacuum chambers, condenser and a pump.
The first chamber maintains 10 to 22 cm vacuum at 90° to 95°C, the second one maintains 35 to 50 cm vacuum at 70°C to 80°C, while the third one maintains 65 to 70 cm vacuum at 40°C to 45°C. The milk product passes through these three chambers one by one. Finally the product goes to a cooler with the help of a pump.
4. Bottle Filling Unit:
Bottle filling machine in a dairy industry is an important item for maintaining efficiency and economy. Mechanical filling of bottles reduces loss of time and increases output per day.
There are two types of mechanical filler:
i. Gravity type
ii. Vacuum type
i. Gravity Type:
There is a circular tank provided with a series of valves around the periphery of the tank. The bottle is kept beneath the valves and as soon as the valve is lifted slightly upward, the valve is opened and the milk starts coming into the bottle. There is a vent pipe provided in the central position of the valve for allowing the bottle to go out.
The following are the disadvantages of this type of bottle filling:
(a) A defective valve leaks to a great extent.
(b) Filling speed is slow and hence large quantities of milk cannot be handled efficiently.
(c) Bottles which are not seated well or distorted in shape, start overflowing while filling.
ii. Vacuum Type Filler:
It consists of a tank which is sealed completely. The inside pressure of the tank is maintained at about 35 cm. There is a float valve provided in the milk tank which maintains the heat of the milk at about 23 cm. The bottle is raised against the rubber ring on the filling valves. Air from the bottle is drawn out through a vertical vacuum pipe. The milk fills the space vacated by air.
5. Bottle Capping Unit:
Bottle capping is as important as bottle filling. As soon as bottle is filled by the milk, it goes to the capping machine where the bottle is capped one by one with the help of mechanical capper. Usually aluminium caps are used which are punched from a continuous strip of thin aluminium foil. The cap is never allowed to be touched by dirty hands. There is some trade mark printed on the cap of the particular dairy industry.
6. Bottle and Can Washing Unit:
Bottle Washing:
Soaker type washing unit is used for large dairy industry.
Bottles undergo the following different treatments:
i. Water at 32°C is used for pre-rinsing the bottle. It is allowed to drain out.
ii. Caustic soda solution at about 63°C is used as detergent.
iii. Detergent at 80°C is jetted from inside and outside of the bottles. It removes all the filth and dirt.
iv. At a temperature of about 60°C, some water is jetted out through the bottle.
v. Fresh water at 35°C is jetted from both sides and the used water is drained out regularly.
vi. Water at 20°C is sprayed from outside to bring the temperature of the bottles sufficiently down, so that cold milk can be filled easily.
Can Washers:
It is necessary to wash, sterilize and dry the cans for milk as soon as it is emptied.
There are two types of washers:
i. Rotary can washer.
ii. Straight through machine.
i. Rotary Can Washer:
Rotary can washer is used for small dairy only. Inverted cans are placed on a platform that rotates under a cover. Arrangement is such that steam vapour can easily escape from the top. It occupies less space.
The various treatments are as follows:
(a) Pre-rinse with water to remove the sticking milk or fat. Water jet under a pressure of about 2 to 3 kg/cm2 is used for this purpose. The treatment is done at about 43°C.
(b) Detergent wash with high velocity warm solution at 75°C is done. Usually sodium silicate or sodium sulphate is used as detergents.
(c) Hot rinsing is done with clean hot water at 75°C.
(d) Hot rinse with clean hot water at 90° to 100°C is done.
Sterilisation is done with the help of super-heated steam at about 105°C. It is for destroying the germs of the can. Drying is done with the air at 110°C.
Pressure gauges and thermometers are used to indicate the pressure and the temperature.
ii. Straight through Machine:
In this method, all the treatments are alike but the loading and unloading of the cans and their lids are done at two opposite ends.
7. Cream Separator:
Cream separator is a device used for separating cream from the milk. Separation is effected by taking advantage of the fact that specific gravity of the fat (0.93) is lower than the milk (average 1.036).
There are two methods of separating cream:
(a) Gravity method
(b) Centrifugal separator
Gravity method is slow and inefficient method and so it is obsolete. Centrifugal separator is a common method.
Cream separator commonly consists of:
(i) Frame
(ii) Worm and driving wheel
(iii) Spindle
(iv) Bowl
(v) Float
(vi) Milk can and faucet.
Milk flows under gravity from milk pan to the bowl. A float valve is there to control the flow of milk. The bowl consists of a number of conical disks, mounted on a spindle. The bowl is an assembly of bowl body, top disc, intermediate disc, bottom disc, cream screw, bowl nut, bowl hood, rubber ring and distributor.
There is arrangement of worm and worm gear for meshing with each other at the lower part of the spindle. The disks rotate at very high speed (6000 to 9000 rev/min). The whole milk is fed in the centre and the milk is divided into thin layers as it enters the space between the disks.
When the disks rotate at very high velocity, the milk fat being lighter in weight, remains in the centre of the bowl. The heavier portion of the milk is thrown to the outer rim of the bowl. Cream screw is provided to control the density of the cream. The cream screw is screwed out if less thicker cream is required.
8. Refrigerator:
The process of lowering the temperature of a substance below that of its surrounding atmosphere is called Refrigeration. The heat extracted from the material by the refrigerant is delivered to the atmosphere by air or water. There are various systems of refrigeration but the most common type used for dairy industry is compression refrigeration system. This system is simple, dependable and easily controllable.
The system consists of following process:
i. Evaporation
ii. Compression
iii. Condensation
iv. Pressure reduction
For achieving these requirements, the system has got:
i. Evaporator
ii. Expansion valve
iii. Compressor and
iv. Condenser
Evaporator is connected with a throttling device called Expansion valve. The liquid refrigerant comes to the evaporator through expansion valve. The evaporator is located within the space where the product is to be cooled. Heat is transferred from the refrigerated substance to the refrigerant. Thus refrigerant is converted into low pressure vapour. This vapour comes to a compressor which is suitably placed in the line.
The compressor has got a piston and a cylinder. The low pressure vapour is compressed by the compressor. This raises the pressure and the temperature of the vapour. This high pressure vapour comes to the condenser unit through discharge pipe.
The condenser is situated between the compressor unit and the expansion valve. Condenser is used for condensing the high pressure vapour into high pressure liquid. This is done with the help of cooling water. The condenser receives the refrigerant at high pressure and temperature in vapour state. As the refrigerant flows in the condenser tubes, water is sprayed on the tubes. The refrigerant cools down to the liquid state. It is collected in a Liquid receiver from where it goes to the expansion valve.
When the high pressure liquid refrigerant reaches the expansion valve, it gets expansion space. Due to this space, the pressure is reduced and refrigerant becomes low pressure liquid. After that the refrigerant enters into Evaporator. The temperature of the space to which the evaporator is exposed, being higher than the boiling point of liquid refrigerant causes the liquid to boil. This refrigerant then goes to compressor in low pressure vapour state and the cycle is repeated again.