Reception includes following operations: Unloading, grading, conveying, sampling,testing, weighing or measuring and recording, dumping and pumping.
i. Unloading
Milk brought either in cans or in tankers is unloaded.
Milk cans: As soon as vehicle carrying milk in cans arrives at the reception dock,the cans are unloaded manually and generally placed on the conveyors. If the level of the truck surface is in line with the platform, the unloading of cans requires least
effort.
Road/Rail tankers: Tanker, after grading and sampling, is connected with the pump and piping and milk is pumped through a flow meter where the volume of milk is automatically recorded.
ii. Conveying
Milk cans are placed on gravity roller or power chain conveyor. The lids are removed and each can is subjected to rapid sensory evaluation and some preliminary tests to decide the acceptance or rejection of the milk.
Conveyors: Conveying systems and related devices must be considered in connection with efficient materials handling to provide direct and continuous flow from a point of origin to the ultimate destination. The conveyor system should be simple, direct,flexible, and free from trouble spots. It should have proper elevation at all points,and easy to clean, lubricate and maintain. Sharp curves, sudden changes of elevation switching of various size packages and other tasks can be handled without difficulty.
Pipelines: In a milk plant, liquids are conveyed from point to point by means of pipes that are joined together and attached to equipment by sanitary pipe fittings.Special metals are needed for the construction of pipe fittings coming in contact with dairy products in order to protect flavour and purity. Stainless steel sanitary pipe is now used throughout the industry. The size, length and joints of piping must be optimized in light of quantity of product to be pumped to desired destination in a given period of time.
Conveyors: Conveying systems and related devices must be considered in connection with efficient materials handling to provide direct and continuous flow from a point of origin to the ultimate destination. The conveyor system should be simple, direct,flexible, and free from trouble spots. It should have proper elevation at all points,and easy to clean, lubricate and maintain. Sharp curves, sudden changes of elevation switching of various size packages and other tasks can be handled without difficulty.
Pipelines: In a milk plant, liquids are conveyed from point to point by means of pipes that are joined together and attached to equipment by sanitary pipe fittings.Special metals are needed for the construction of pipe fittings coming in contact with dairy products in order to protect flavour and purity. Stainless steel sanitary pipe is now used throughout the industry. The size, length and joints of piping must be optimized in light of quantity of product to be pumped to desired destination in a given period of time.
iii. Examination of Raw Milk
Raw milk has to pass through rigorous examination which may include organoleptic,physical and chemical tests to assess the quality of intake milk rapidly, and decide for its acceptance or rejection. All these tests known as “platform tests” are performed on each can/tanker to assess the quality of the incoming milk before it is accepted and weighed. These tests must be easy to perform, give quick and reliable results and should not require complicated and elaborate equipment. The classification of milk on the basis of quality is usually referred to “grading of milk”.So grading of milk is done on the basis of platform tests which include organoleptic
as well as preliminary tests.
Purpose: Milk received is further subjected to some sort of processing including heat processing for manufacturing products, and finally marketed to consumers. A good quality product cannot be made from bad quality raw ingredients. So, quality and composition of raw milk must be checked for freshness, hygiene and conformity to the legal standards. These can be accomplished by examination of raw milk through platform and other laboratory tests. Accordingly, the main purposes of examination of raw milk at reception dock are assessment of (i) freshness, (ii) hygienic quality, and (iii) composition.
Organoleptic tests: Organoleptic or sensory tests are performed with the help of five sensing organs, viz. eye, nose, tongue, ear and skin. The general appearnce,cleanliness, colour, taste and smell of milk are tested before emptying the transport containers.Milk in can is evaluated while moving on the conveyor. Organoleptic tests are quick, cheap and with growing experience of the assessor, very reliable. Since practically no equipment is needed, the sensory test can be carried out anywhere and anytime. However, sensory tests are subjective and would depend on the assessor’s faculty of perception.
Smell or odour: Just after opening the lid of the container, sniffing will detect the smell/odour of the milk. Normal milk should not have any off-or unnatural smell in it. If the smell is slightly sour, the milk might have undergone microbial deterioration.
Appearance: After the odour test, milk in each can is observed for any floating extraneous matters, off-colour, or partially churned milk. Normal milk should be free from these. Presence of visible dirt, straw or manure indicates that milk has been handled in an unhygienic way. The colour of milk of cows and sheep should be slightly yellowish-white, that of buffaloes and goat absolutely white. If the colour is reddish, the milk may contain blood; if it is yellowish, it may contain pus, such milk may be secreted from infected udder (mastitis) and should not be accepted.
Taste: Taste of milk can be noted by taking a spoonful milk in the mouth and rotating inside with the help of tongue. When doubt exists concerning smell, the taste of the milk may help to determine sourness and if so, milk should be rejected.Adulteration of milk with salt, sugar, etc. can also be detected by taste and found positive must be rejected.
Temperature: With practice, the grader can judge the temperature of milk with a high degree of accuracy by touching the container. Abnormal to the weather or condition may indicate the prehistory of milk with respect to its cooling or heating,etc.
Preliminary tests: Preliminary tests as discussed below. These are simple and rapid physical-chemical tests which can be performed easily on the reception dock:
Clot-On-Boiling (C.O.B.): A small portion of milk is heated to boiling point in a test tube for checking whether it withstands heat treatment without clotting. If the milk clots on boiling it is sour or abnormal. This milk cannot be processed any more and hence it should be rejected.Alcohol test: Milk with increased acidity or of abnormal salt balance or mastitis flocculates after addition of alcohol. This test is used to determine heat stability of milk. If no flocculation occurs after addition of alcohol, the milk is fresh or its acidity is only very slightly increased. If milk flocculates with alcohol, the milk is heat unstable and it should be rejected.
Titratable acidity (T.A.): The titratable acidity of milk is determined by titrating 10 ml of milk with N/9 NaOH solution to assess sourness in milk. The result is either expressed in degrees Dornic, i.e. ml of N/10 NaOH used being equal to 1 degree Dornic(Do) or in % lactic acid, whereby ml of N/10 NaOH used is equal to 0.01% w/v lactic acid. Milk testing more than 0.15% lactic acid should be rejected.
pH: The pH value can be measured with an electronic pH meter or with the help of different pH-indicators to assess the acidity of milk. Normal milk has pH ranging from 6.6 (in cow milk) to 6.8 (in buffalo milk). A higher pH (7.0 to 7.4) means milk from infected (mastitis) udders or it is neutralized by alkali. The major shortcoming of this method is its poor sensitivity since milk is extremely well buffered system,slight change in acidity or alkalinity cannot be detected.
Lactometer test: Lactometer is used for determination of specific gravity. However,test result obtained can be misleading due to variation in temperature and fat content in milk etc. This method is correct only when carried out at the correct temperature and combined with milkfat test.
Sediment test: The sediment test is used to check the visible foreign matter contained in the milk. Off the bottom sediment tester or barrel type sediment tester may be used. Test is carried out by allowing a measured quantity of milk (usually 500 ml) to pass through a fixed area of a filter disc and comparing the sediment left with the prepared standard (Table). Any hair flies, pieces of hay or straw or any large particles of dirt are not included in grading sediment. Presence of appreciable sediment indicates careless or insanitary dairy farm practice. However lack of sediment is not always indicative of ideal conditions, since visible sediment may be readily removed by straining at the dairy farm. It may have bacterial contamination.
Purpose: Milk received is further subjected to some sort of processing including heat processing for manufacturing products, and finally marketed to consumers. A good quality product cannot be made from bad quality raw ingredients. So, quality and composition of raw milk must be checked for freshness, hygiene and conformity to the legal standards. These can be accomplished by examination of raw milk through platform and other laboratory tests. Accordingly, the main purposes of examination of raw milk at reception dock are assessment of (i) freshness, (ii) hygienic quality, and (iii) composition.
Organoleptic tests: Organoleptic or sensory tests are performed with the help of five sensing organs, viz. eye, nose, tongue, ear and skin. The general appearnce,cleanliness, colour, taste and smell of milk are tested before emptying the transport containers.Milk in can is evaluated while moving on the conveyor. Organoleptic tests are quick, cheap and with growing experience of the assessor, very reliable. Since practically no equipment is needed, the sensory test can be carried out anywhere and anytime. However, sensory tests are subjective and would depend on the assessor’s faculty of perception.
Smell or odour: Just after opening the lid of the container, sniffing will detect the smell/odour of the milk. Normal milk should not have any off-or unnatural smell in it. If the smell is slightly sour, the milk might have undergone microbial deterioration.
Appearance: After the odour test, milk in each can is observed for any floating extraneous matters, off-colour, or partially churned milk. Normal milk should be free from these. Presence of visible dirt, straw or manure indicates that milk has been handled in an unhygienic way. The colour of milk of cows and sheep should be slightly yellowish-white, that of buffaloes and goat absolutely white. If the colour is reddish, the milk may contain blood; if it is yellowish, it may contain pus, such milk may be secreted from infected udder (mastitis) and should not be accepted.
Taste: Taste of milk can be noted by taking a spoonful milk in the mouth and rotating inside with the help of tongue. When doubt exists concerning smell, the taste of the milk may help to determine sourness and if so, milk should be rejected.Adulteration of milk with salt, sugar, etc. can also be detected by taste and found positive must be rejected.
Temperature: With practice, the grader can judge the temperature of milk with a high degree of accuracy by touching the container. Abnormal to the weather or condition may indicate the prehistory of milk with respect to its cooling or heating,etc.
Preliminary tests: Preliminary tests as discussed below. These are simple and rapid physical-chemical tests which can be performed easily on the reception dock:
Clot-On-Boiling (C.O.B.): A small portion of milk is heated to boiling point in a test tube for checking whether it withstands heat treatment without clotting. If the milk clots on boiling it is sour or abnormal. This milk cannot be processed any more and hence it should be rejected.Alcohol test: Milk with increased acidity or of abnormal salt balance or mastitis flocculates after addition of alcohol. This test is used to determine heat stability of milk. If no flocculation occurs after addition of alcohol, the milk is fresh or its acidity is only very slightly increased. If milk flocculates with alcohol, the milk is heat unstable and it should be rejected.
Titratable acidity (T.A.): The titratable acidity of milk is determined by titrating 10 ml of milk with N/9 NaOH solution to assess sourness in milk. The result is either expressed in degrees Dornic, i.e. ml of N/10 NaOH used being equal to 1 degree Dornic(Do) or in % lactic acid, whereby ml of N/10 NaOH used is equal to 0.01% w/v lactic acid. Milk testing more than 0.15% lactic acid should be rejected.
pH: The pH value can be measured with an electronic pH meter or with the help of different pH-indicators to assess the acidity of milk. Normal milk has pH ranging from 6.6 (in cow milk) to 6.8 (in buffalo milk). A higher pH (7.0 to 7.4) means milk from infected (mastitis) udders or it is neutralized by alkali. The major shortcoming of this method is its poor sensitivity since milk is extremely well buffered system,slight change in acidity or alkalinity cannot be detected.
Lactometer test: Lactometer is used for determination of specific gravity. However,test result obtained can be misleading due to variation in temperature and fat content in milk etc. This method is correct only when carried out at the correct temperature and combined with milkfat test.
Sediment test: The sediment test is used to check the visible foreign matter contained in the milk. Off the bottom sediment tester or barrel type sediment tester may be used. Test is carried out by allowing a measured quantity of milk (usually 500 ml) to pass through a fixed area of a filter disc and comparing the sediment left with the prepared standard (Table). Any hair flies, pieces of hay or straw or any large particles of dirt are not included in grading sediment. Presence of appreciable sediment indicates careless or insanitary dairy farm practice. However lack of sediment is not always indicative of ideal conditions, since visible sediment may be readily removed by straining at the dairy farm. It may have bacterial contamination.
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| Quality of Milk by Sediment Test |
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| Quality of Milk by Alizarin-Alcohol Test |
Alizarin-alcohol test: Incorporation of alizarin in alcohol helps
to determine both heat stability and approximate percentage of acidity
in milk. Milk showing poor heat stability is rejected.
iv. Tilting/Emptying of Milk Cans
Acceptable milk in cans are lifted manually from the conveyor, rested on floor mounted can tipping cross bar padded with rubber and tilted to drain the milk into weigh bowl. When the can tipping device is used, the operator must hold the can until the milk drains from it and then convey the emptied can by hand to the washer via drip saver. For quick, easy and high speed, a dump grid, suspended over the weigh tank, is used on which the can drains and is automatically moved to the can washer.
v. Weighing/Measuring and Recording of Milk
The milk in cans is dumped into the weigh tank/bowl, of single or double compartment,either manually or mechanically. The stainless steel weigh bowl of 250 or 500 Kg capacity is attached to a circular dial weigh scale and the portion towards the outlet valve overhangs with anti-splash stainless steel strainer. The outlet valve of weigh bowl is suited for manual or air actuated operation. The operator makes direct reading of the weight of the milk on the scale and records it separately for individual suppliers. Automatic printing of weight is also possible. The milk in tanker (road/rail) may be measured in volume by passing it through a flow-meter or in weight by using a weigh bridge where tare weight of the tanker is deducted from gross weight of it.
vi. Sampling of Milk
Samples may be drawn during reception of milk for chemical and microbiological analysis in the laboratory. Only representative sample, without any type of adulteration, dilution and contamination should be drawn using correct technique and appropriate device. While strict precautions regarding sterility of the stirrer,sampler, container, etc. are required for obtaining a microbiological sample and dryness and cleanliness of the above appliances should suffice for a chemical sample. Test cannot be accurate unless the test sample is truly representative of the product to be tested. Samples from milk containers may be drawn with the help of a suitable device. The characteristics of various devices have been listed in Table.
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| Characteristics of Milk Sampling Devices |
Sampling methods: Sample should be taken after thorough mixing of milk with the help of plunger or sampler (devices) or some other means.
i) From a small handy batch: Milk is properly mixed before taking sample.
ii) From a large batch: Milk in can or vat or small tank can be mixed by using a plunger manually. Minimum ten times from top to bottom plungering will ensure adequate mixing before drawing sample. Mechanical stirring can also be done wherever facilities available. Vigorous stirring is avoided as milk may get churned at temperatures between 26.5 and 29.5 0C.
iii) From several containers of different size, shape and type: If a large vat is available, milk of all the containers are mixed in vat and a sample is drawn.
iv) From bulk units: Nos. of cans filled from storage tank/bulk unit is not required to be sampled individually. The number of random cans to be sampled shall be as follows:
v) From storage tanks/rail/road tankers: Method of sampling is governed by storage/transport conditions. So, no rigid procedure of sampling can be prescribed.However, a recommended procedure described below may be followed.
Milk is thoroughly mixed by using either a sufficiently large plunger or a mechanical agitator or compressed air till a complete agreement is obtained between samples taken at the manhole and the outlet cock with respect to Fat and SNF. Plunger is inserted through manhole and, pushed forward and pulled back, downward and back, and backward and back in cyclic order repeatedly for not less than 15 minutes. Sampling is done through the stopcock in the tank door or from a valve in the discharge line from the tank as it is being emptied.
Milk is thoroughly mixed by using either a sufficiently large plunger or a mechanical agitator or compressed air till a complete agreement is obtained between samples taken at the manhole and the outlet cock with respect to Fat and SNF. Plunger is inserted through manhole and, pushed forward and pulled back, downward and back, and backward and back in cyclic order repeatedly for not less than 15 minutes. Sampling is done through the stopcock in the tank door or from a valve in the discharge line from the tank as it is being emptied.
vii. Dumping of Milk
After weighing and recording, the milk can be discharged into the dump tank situated below through stainless steel chute between the weigh bowl and dump tank. Dump tank should be of sufficient capacity to avoid delay or overflow of milk,at least one and half times but not more than 3 times the capacity of the weigh bowl. An electronic milk level control may be installed in the dump tank to eliminate the possibility of loss of milk from overflow.
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