UNIT 11 PACKAGING, STORAGE AND COMMON DEFECTS IN CONDENSED MILKS Structure 11.0 Objectives 11.1 Introduction 11.2 Packaging 11.3 Storage 11.4 Judging and Grading 11.5 Defects their causes and Preventive Measures 11.6 Uses milk 11.7 Let Us Sum Up 11.8 Key Words 11.9 Some Useful Books 11.10 Answer to Check Your Progress 11.0 OBJECTIVES After reading this we shall be able to know about the packaging of Condensed milk and Evaporated milk. know about storage of the product. judge and Grade the product identify known defects, their Causes and Prevention know the uses of Condensed milk and Evaporated milk 11.1 INTRODUCTION It is absolutely essential to maintain the quality of good grade concentrated milk during storage until it reaches the intended customer. Selection of proper packaging materials and storage conditions will ensure prolonged keeping quality of the product. In the manufacture of different types of concentrated milks care should be taken to produce uniform acceptable quality product. Routine examination of the product is important, not only to assure improvement in the product, but also to see that it reaches the customer in good condition. In this respect, it is helpful to know and understand how to evaluate and grade good quality product. If however, certain defects are noticed in the product the reasons for the same and the preventive steps to be taken to eliminate defects should also be known to the manufacturer. 11.2 PACKAGING 36 Packaging essentially means placing a commodity into a protective wrapper or container for transport or storage or both. Thus package must perform the following important functions.
Contain the product Protect the product Packaging, Storage and Common Defects in Condensed Milks Help in selling the product Concentrated milk is packed in suitable containers for storage and transport. Sweetened condensed milk is packed at the end of the manufacturing process. Evaporated milk is packed in containers immediately after concentration and then sterilized with the container. In case of Ultra High Temperature (UHT) treated milk, the product is sterilized and then aseptically packed in suitable containers. i. Packaging of Condensed Milk Two types of packages are used. For large quantity or for bulk transport, the condensed milk is filled in barrels of various sizes ranging from 50kg to 300 kg. The barrels are made either from wood or metal. Barrels are coated internally with wax or provided with polythene liners. Before condensed milk is run into barrels, they should be sterilized by means of steam, condensate allowed to drain and then filled by means of a funnel placed in the bunghole. When the barrels are full, the bungs are driven in, thus effectively, sealing the content. The room in which the barrels are filled should be in sanitary condition and its atmosphere should preferably be one of filtered air. Condensed milk is usually filled in barrels, at around 15.5 C (60 F). For retail sale the condensed milk is packed in cans of various sizes from 200 gms to 5 kg or even more. The method used for can filling varies from hand filling to continuous automated filling. In big factories tin sheets are shaped into cans by machines, which are then filled and sealed immediately. In small factories the cans are bought readymade and filled and sealed either manually or by machines. Sealing is carried either by means of solder or by crimping on the tops of the cans to form an airtight seal without the use of solder. The cans should be sealed immediately after they have been filled in order to prevent contamination of the product by exposure to atmosphere. Since cans filled with condensed milk do not undergo subsequent sterilization, strict sanitary conditions should be observed during filling process so as to prevent contamination which will otherwise affect the keeping quality of the stored product. The filling and sealing area should be enclosed and only filtered air should be circulated to avoid direct exposure to atmospheric dirt or dust during filling. The filling machines and accessories should be thoroughly washed and sanitized before start of the filling operation. The cans and lids on their passage to the filler should be suitably sterilized. This is usually done by passing the cans under or over a battery of suitable gas jets. Personnel operating the filling and sealing machines should observe sanitary habits. It is important to fill cans fully so as to exclude as much air from the container as possible and seal them promptly after filling. ii. Packaging of Evaporated Milk Several machines have been designed for this purpose. In one type, which is known as Vent hole type concentrated milk is filled through a small aperture (3 mm of 1/ 8 inch diameter). After cans have been filled they are immediately sealed. Sealing process requires care, as the seal has to with stand the heat of sterilization process. It is also essential that cans are filled as quickly as possible to avoid contamination of milk. The opening in the cans is usually soldered by mechanical finger. But hand soldering is also practiced while handling smaller number of cans. When the cans leave the sealing machine they are tested for leaks by being plunged into a hot water tank. If any of the tins rise or give off air bubbles, they are discarded as unfit for sterilization. Modern sealing processes are so rapidly carried out that a large number of cans may be sealed in one minute. In this process open or sanitary type cans are 37
Concentrated Milks used. The concentrated milk is filled into the open can one end of which is already seamed and after filling the other end of the can is seamed by an automatic seaming machine. 11.3 STORAGE OF CONDENSED MILKS Both condensed milk and evaporated milk are expected to be stored for longer period. Hence conditions should be maintained such that the product should not deteriorate in quality during storage. The room at which the product is stored is one major factor, which will have definite effect on the keeping quality. The present trend is to store both condensed milk and evaporated milk around 10 to 15 C. Very low such as 0 C or below may cause sugar separation in condensed milk leading to a defect called sandiness in the product. The sandiness is due to the presence of very large crystals of lactose. Viscosity of the product also will increase due to low storage. Increase in viscosity may be beneficial up to a certain level, but very high viscosity changes due to low storage may also affect the body and texture characteristics of the product. It has been shown that commercial evaporated milk remains acceptable even after two years when stored below 15 C but deteriorates rapidly when stored at 21 C or above. Humidity of the storage space should also be kept low (below 50%) to check the spoilage of cans and labels. Periodic inversion of cans in case of evaporated milk during storage will help to minimize fat separation. Check Your Progress 1 38 1. What you understand by the term packaging? 2. What important functions must package provide? 3. How condensed milk is packed for bulk transport? 4. Why strict sanitary conditions should be maintained during packaging of condensed milk? 5. Why storage is important in case of condensed milk?
6. What is the recommended storage of condensed and evaporated milk? 7. What happens when condensed milk is stored at a very low such as 0 C or below? Packaging, Storage and Common Defects in Condensed Milks 11.4 JUDGING AND GRADING Good and acceptable quality food products are made by selecting good quality raw materials and following the established manufacturing techniques. This is also true with the manufacture of condensed milk and evaporated milk. Proper care should be taken to produce good quality product. Manufacturer should routinely examine the product to judge its quality and to maintain the grade that is acceptable to customers. Judging refers to the act of evaluating the dairy product for its Eating quality on the basis of various attributes. Grading refers to its classification into different categories or grades. The eating quality of a dairy product is generally determined by organoleptic/sensory tests, which include all the five senses of sight, smell, taste, touch and sound. Of these taste and smell are the most important in judging and grading. There are various methods available for judging and grading of dairy products. Some of the subjective tests based on organoleptic examination such as flavour, taste etc. make use of the hedonic scale or variation of it. i. Hedonic Scale: This method of rating for individual attributes is simple and gives a clear indication of the particular attribute of the product. For example the flavour of a dairy product may be evaluated on a hedonic scale rating from 1-10 points as suggested in the following Table 11.1. Modification of hedonic scale using narrow range 1-5 may also be used in evaluating the product. Table. 11.1 Hedonic scale for flavour Sensory Reaction Score Superior 10 Excellent 9 Very desirable 8 Desirable 7 Slightly desirable 6 No strong likes 5 Slightly undesirable 4 Moderately undesirable 3 Undesirable 2 Objectionable, Offensive 1 39
Concentrated Milks ii. Score card: The scorecards for condensed milk and evaporated milk proposed by the American Dairy Science Association (ADSA) were most useful in establishing standards and obtaining uniform high quality products. Table 11.2 Score Card for Condensed Milk (ADSA) Items Perfect Score Flavour and odour 30 Body and texture 25 Colour 05 Fat content 10 Milk Solids 10 Bacteria 10 Sugar 10 Adulterants and preservatives must be absent TOTAL SCORE= 100 Table 11.3 Score Card for Evaporated Milk (ADSA) Items Perfect Score Flavour and odour 40 Body and texture 25 Colour 05 Fat content 10 Milk Solids 10 Total Solids 10 Adulterants and preservatives must be absent TOTAL SCORE = 100 40 These score cards considered such items as (a) flavour and odour; (b) body and texture; (c) colour; (d) fat content; (e) milk solids; (f) bacteria and (g) sugar in case of condensed milk only). Numerical values were assigned to each item. Flavour/ odour and body/texture were given higher ratings (30 and 25 points in case of condensed milk and 30 and 25 points in case of evaporated milk). Colour rated 5 points while all other items were treated equally being allotted 10 points each. The following procedure should be followed for judging a product. i) Sampling: Select a can of the product at random for examination. Sequence of observations: Avoid undue agitation when transporting to the laboratory. Place it on the table for examination in the same upright position as before. Cut more than three fourths of the top of the can and turn it back. Then examine in the following order. ii) Appearance of the can: Look for signs of rust etc., both outside and inside (when emptied). iii) Appearance of the product: Examine uniformity of colour; look for absence of lumps in condensed milk and cream layer/butter/particles/curd in evaporated milk.
iv) Body and texture (viscosity): Observe whether the viscosity is high, normal or low while pouring the contents into a beaker. v) Sediment: Watch for presence or absence of sediment at the bottom of the container when emptied. vi) Flavour and odour: Note defects if any, by placing a small spoonful of condensed milk or diluted evaporated milk (1:1 with distilled water) on the tongue. vii) Laboratory Tests: Take a sample aseptically and then test for fat, total solids, bacteria, sugar, adulterants and preservatives. iii. Requirements for High Grade Condensed milk and Evaporated milk: The person who is judging the product should be familiar with the desirable qualities of the product as well as the possible defects, which may occur in both condensed milk and evaporated milk. a) Condensed milk: It should have a clean, pleasant aroma, a pronounced sweet taste, smooth and uniform body and texture and uniform light colour, which should be yellow for cow milk and light greenish white for buffalo milk. b) Evaporated Milk: It should have mild pleasant flavour, a relatively viscous body, uniformly smooth in texture and uniform colour. Packaging, Storage and Common Defects in Condensed Milks 11.5 DEFECTS THEIR CAUSES AND PREVENTION Condensed milk and evaporated milk are the products suitable for prolonged storage. They have typical properties after production by which they are identified. These properties must be such that the product is fit for sale immediately after production and does not alter during reasonable period of storage. They should, therefore be physically, chemically and bacteriologically fit for human consumption by the end of storage period. Routine examination of the product soon after manufacture as well as during storage may be carried out to judge the quality of the product. If any defect is noticed, proper care should be taken to climate the defect in the subsequent batches. It is, therefore, important to know what type of defects may occur in the product, the reasons for their occurrence and the preventive measures to be used to avoid these defects. The defects which may occur in condensed milk may be divided into two categories as follows: Microbial defects Non-Microbial defects i. Microbial Defects These defects are due to presence of abnormal bacteria in the milk or in products. The common defects are as follows: a) Gassy fermentation/bloats: Formation of gas takes place in cans and barrels of condensed milk causing bulging or bursting of containers. Gas producing yeasts are the cause of many types of gaseous fermentation. The source of contamination may be the raw milk, or inferior quality sugar or unhygienic factory conditions especially not properly washed and sanitized equipments and filling machine. 41
Concentrated Milks To avoid this defect good quality raw milk and properly preheating should be used. Only good quality sugar without any yeast contamination should be selected. Proper sanitary conditions should be maintained during manufacture and packaging of condensed milk. The containers should be filled fully with little space for air or oxygen. (b) (c) Bacterial thickening: Condensed milk gets thickened progressively during storage. This is due to microorganisms which produce rennin like enzyme. These organisms are easily destroyed during preheating process. Optimum sugar ratio (64.5) may inhibit the growth of microorganism. Low storage also helps in reducing the bacterial thickening. Mould buttons: This defect occurs during storage due to mould contamination. Small reddish brown pieces of curd about ¼ to ¾ in diameter are formed on the surface causing localized coagulation. This defect occurs after storing the product for some time. The causative mould Aspergillus repeno produces a clotting enzyme which causes localized clotting. High storage also helps in the growth of the organism. The milk may be infected with the organism during concentration process. To avoid this defect, scrupulous cleaning and care of dairy equipments is essential. Since this organism does not grow at low storing of condensed milk at lower will prevent this defect. ii. Non Microbial Defects The non-microbial defects are of chemical or physical origin. These are listed below. (a) Sandiness: Good quality condensed milk should possess a smooth homogenous texture and be pleasant to palate. Some times however the milk may be gritty containing large number large sized hard lactose. The solid particles are of such size that the product lacks smoothness and grittiness is noticeable, as the sample is being tasted. This defect is readily detected by an average consumer. Sandy, rough grainy, granular, and gritty are the term used to describe this defect. 42 (b) The sandiness may be due to presence of relatively large size crystals of lactose. Also if excess amount of sugar is used in manufacture of condensed milk, sugar particles may also crystallize out and cause sandiness. If manufacturing conditions are not conducive to the formation of small lactose crystals, large and coarse crystals are formed. Cooling of condensed milk must be carried out in such a manner that smooth texture is obtained by the formation of large number of minute sugar crystals. High viscosity also delays the crystal formation. It is, therefore, necessary to rapidly cool the condensed milk in the initial stages. Correct cooling and induced rapid crystallization with correct amount of seed lactose will help to avoid this defect. Optimum storage is also essential to avoid this defect. Age thickening: Thickened condensed milk is the most common defects seen in the sweetened condensed milk. This defect varies markedly in its intensity from slight jelly to a firm and consistency. The defect becomes progressively more intensive upon storage, especially at room or above. Preheating of milk and degree to which the milk is concentrated have been observed to have profound effect on age thickening. With high pre-
heating s, there is a greater tendency upon the product to thicken early. With increasing concentration of milk solids the thickening tendency becomes more marked. In order to avoid early thickening of condensed milk, optimum pre heating should be maintained. Sugar should only be added at the end of condensing of milk. The product should preferably be stored at below 15 C with the addition of proper type of stabilizers age thickening may be decreased to a great extent. Packaging, Storage and Common Defects in Condensed Milks (c) (d) Brown colour: usually brown colour discolouration is associated with age thickening, both of which become progressively more intense on storage. The acidity and of storage are factors, which determine the rapidity of change. This defect may be avoided if the condensed milk cans are stored at reasonably low s. Other defects in condensed milk include some flavour defects such as rancid, tallowy, metallic etc. Following good manufacturing practices, good quality raw material, good quality milk, good packaging and storing the product at low may help to avoid the defect. Fat separation in condensed milk is rare. Defects in Evaporated Milk: Evaporated milk is sterilized product. If sterilization is properly carried out the product will remain in good condition without any bacterial spoilage during storage. However, if sterilization process is improperly carried out, some microorganisms and spore may, survive and cause spoilage, during storage, Gassy fermentation, coagulation, bitterness and fishy flavour are some of the defects noticed in improperly sterilized evaporated milk. If the bacterial defect in evaporated milk is to be eliminated, it is essential that the sterilization process should be carried properly and adequately with strict cleanliness in the factory. Chemical/Physical defects in Evaporated Milk Age thickening Age thinning Fat separation Sediments/mineral deposit Brown colouration (a) Age thickening: As in the case of sweetened condensed milk thickening or high viscosity of the product is due to improper preheating of milk, higher total solids concentration, inadequate homogenization and storage at higher. To eliminate this defect the milk should be heated at optimum preheating s. The concentrated milk should be homogenized at proper pressure and the product should be stored at low. (b) (c) Age thinning/low viscosity: Milk like consistency of evaporated milk indicates its low viscosity. This defect may be due to insufficient concentration of milk and inadequate or no homogenization of milk or improper sterilization. This defect is eliminated by following correct/adequate processing conditions and storing the product at low. Fat Separation: A thick, heavy cream layer is noticed at the top of the can when it is opened. The cream layer is very dense and will not easily mix with 43
Concentrated Milks remainder of milk. Even after mixing creamy chunks of butter particles are noticed floating in the milk of relatively low viscosity. The reasons for this defect to appear are in adequate homogenization high storage, long storage period and improper handling during storage. Proper homogenization, low storage and correct handling of the product will eliminate this defect. A more viscous is desirable from fat separation point of view. (d) (e) Sediments/Mineral deposit: Sediments noticed in evaporated milk cans may be due to crystallization of some of the calcium and magnesium salts, and denatured proteins. This gritty sediment formation takes place during prolonged storage of evaporated milk. The rapidity with which the sediments are formed is influenced by the nature of the milk, conditions of manufacture and of storage. Selection of good quality milk, correct processing conditions and low storage will help to eliminate this defect. Higher viscosity product is less prone for this defect. Brown Colour: The brown colour in evaporated milk is associated with high sterilization, high storage and longer storage period. The sterilization should be as low as possible with germicidal efficiency. The brown colour defect in evaporated milk is eliminated by employing proper preheating, correct sterilization process and low for storage of the product. 3.6 USES OF CONDENSED MILK AND EVAPORATED MILK The concentrated milk is used in a variety of food products. The uses of condensed milk and evaporated milk are listed below. i. Condensed Milk finds the following uses It is easily reconstituted by dilution with water to the equivalent concentration of raw milk and used in the preparation many sweetened milk drinks. It is used as sweetening and whitening agent in tea, and coffee beverages. It is used in ice cream preparation. It is used extensively in the preparation candy, chocolate and other confectionery products. It is used in many types of puddings and prepared foods. ii. Evaporated Milk finds the following uses Because, in its homogenization and sterilization evaporated milk finds use infant feeding due to formation of soft curd in the stomach. It is used for reconstitution into milk with water. It is used as an ingredient in the preparation of many types of pudding, sauces and gravies because of its smooth consistency. It is used in the manufacture of ice cream. 44 It is used in the preparation of chocolate, bakery and confectionery products.
It is used in lieu of cream in coffee, tea, cocoa or chocolate. It is diluted with milk and cream to produce coffee cream. Check Your Progress 2 1. What does judging and grading refer to? 2. How eating quality of dairy products generally determined? 3. Name two sensory tests, which are considered important in judging and grading of dairy products. 4. What items are considered in the score card proposed by American Dairy Science Association (ADSA) for condensed milk and evaporated milk? 5. What are the requirements for high grade condensed milk? 6. What is the requirement for high-grade evaporated milk? 7. What are the causes of following defects in condensed milk? a) Gassy fermentation... b) Sandiness... c) Age thickening... 8. What are the causes of following defects in evaporated milk? i) Fat separation... ii) Sediments or Mineral deposit... iii) Brown colour... Packaging, Storage and Common Defects in Condensed Milks 45
Concentrated Milks 9. Name any three uses of condensed milk. 10. Name any three uses of evaporated milk. 11.7 LET US SUM UP Sweetened condensed milk is packaged under strict hygienic and sanitized conditions at the end of the manufacturing process. These packages are not sterilized after packaging. Evaporated milk is packaged in containers immediately after concentration under strict conditions of hygiene and then subjected to sterilization along with the container. In case of Ultra High Temperature (UHT) treated milk, the product is sterilized and then aseptically packed in suitable containers. Wooden or metal barrels coated internally with wax or polythene liners are used for bulk packaging of condensed milk. For retail packaging, cans of various capacity i. e., 200 g to 5 kg or more are used, which can be filled and sealed manually or by machines. Evaporated milk is filled by automatic filling machines into open or sanitary type cans and seamed by an automatic seaming machine, sterilized and stored. Ideal for storing both condensed and evaporated milk is 10 to 15 C. Very low such as 0 C and below may cause sugar separation and increase in viscosity leading to a texture defect called sandiness in condensed milk. Humidity in the storage room should be below 50 % to check the spoilage of cans. Evaporated milk is stable for about two years or more, when stored at 15 C. In general, condensed milk should have a clean, pleasant aroma, a pronounced sweet taste, smooth and uniform body and texture and uniform light colour, which should be yellow for cow milk and light greenish white for buffalo milk. Evaporated milk should have mild pleasant flavour, a relatively viscous body, smooth texture and uniform colour. Sweetened condensed milk may develop bacterial defects like gassy fermentation/bloats, bacterial thickening, mould buttons due to bacterial contamination and sandiness, age thickening, brown colour and fat separation due non-bacterial caused during storage. Evaporated milk being a sterilized product may exhibit age thickening, age thinning, fat separation, sediments/mineral deposit and brown colouration due improper processing and storage when stored for a long time. Condensed Milk is used for reconstitution and in the preparation of many sweetened milk products. It is used as a sweetening and whitening agent in tea and coffee beverages; ice cream, candy, chocolate and other confectionery products, puddings & prepared foods. On the otherhand, evaporated milk finds application in infant foods, reconstitution into milk, preparation of puddings, sauces & gravies, manufacture of ice cream, chocolate, bakery & confectionary products etc. 11.8 KEY WORDS 46 Hedonic Scale : is a simple scale which the range from 1-10 for rating of individual attributes of the products.
ADSA Score Card : is a 100 point score card proposed by American Dairy Science Association for condensed and evaporated milks for rating their sensory, chemical and microbial characteristics. Packaging, Storage and Common Defects in Condensed Milks Gassy fermentation/bloats : is the formation of gas in cans and barrels of condensed milk causing bulging or bursting of containers. Bacterial thickening : is the thickening of condensed milk during storage due to microorganisms producing rennin like enzyme. Mould buttons : is the localized coagulation on the surface of stored condensed milk and is caused by a mould namely, Aspergillus repeno. Sandiness : sandy, rough grainy, granular, and gritty texture observed in condensed milk due to presence of relatively large size crystals of lactose. Age thickening : slight jelly to a firm curd like consistency found in condensed milk due to high preheating of milk, higher degree of concentration, early addition of sugar during condensing and storage at above 15 C. Age thinning : is the lower viscosity of the evaporated milk due to insufficient concentration of milk or inadequate or no homogenization of milk or improper sterilization. 11.9 SOME USEFUL BOOKS Sukumar, De. (1980) Outline of Dairy Technology Oxford University Press Nilson, J.A and Trout, G.M (1964) Judging of Dairy Products AVI. Publ Co. New York 11.10 ANSWERS TO CHECK YOUR PROGRESS Your answers should include the following points Check Your Progress I 1) i) Packaging essentially means placing a commodity into a protective wrapper or container for transport or storage or both. 2) i) The package must provide the following important functions: Contain the product. Protect the product. Help in selling the product. 3) i) For bulk transport condensed milk in filled in barrels of various sizes ranging from 50 kg to 300 kg. 47
Concentrated Milks 4) i) In order to avoid any contamination after the manufacture of the product it is essential to maintain sanitary conditions during packaging. 5) i) The room at which condensed milk is stored is a major factor, which will have definite effect on the keeping quality. Hence conditions should be maintained such that the product should not deteriorate in quality during storage. 6) i) The present trend is to store the product around 10-50 C 7) i) Very low storage may cause sugar separation in condensed milk leading to a defect called sandiness in the product. Check Your Progress II 1) i) Judging refers to the act of evaluating a dairy product for its eating quality and grading refers to its classification into different categories or grades. 2) i) The eating quality of a dairy product is generally determined by organoleptic/ sensory tests, which include all the five senses of sight, smell, taste, touch and sound. 3) i) Taste and smell are the most important in judging and grading. 4) i) Association (ADSA) for condensed milk and evaporated milk? The scorecard considered such items as a) flavour and odour; b) body and texture; c) colour; (d) fat content; e) milk solids; f) bacteria and g) sugar (in case of condensed milk) 5) i) It should have a clean, pleasant aroma, a pronounced sweet taste, smooth and uniform body and texture and uniform light colour which should be yellow for cow milk and light greenish white for buffalo milk. 6) i) It should have mild pleasant flavour, a relatively viscous body, uniformly smooth in texture and uniform colour. 7) i) Defects in sweetened condensed milk. S. No. Name of the defect Cause Prevention 48 1. Gassy fermentation/bloats Contamination with and growth of yeast Storage at high 2. Sandiness Incorrect cooling and crystallization Excessive low storage Excessive sugar ratio 3. Age thickening Excessive pre-heating Adding sugar before fore warming/preheating Storage at high Avoid contamination with yeast Correct cooling and crystallization Optimum low storage Correct sugar ratio Optimum preheating Adding sugar at the end of condensing Storage at low (10 C)
8) i) Defects in evaporated milk: S. No. Name of the defect Cause Prevention 1. Fat separation Homogenization not proper Storage at high Long storage 2. Sediments/ Mineral deposit Crystallization of calcium/magnesium salts Denatured proteins Long storage 3. Brown colour Excessive high heat treatment High storage Prolonged Storage Adequate homogenizati on Storage at low Proper handling during storage Selection of good quality milk Low storage correct heating and sterilization process Low storage Shorter storage period Packaging, Storage and Common Defects in Condensed Milks 9) i) Condensed milk is used for Coffee and tea preparation. Ice cream manufacture. Candy and confectionary 10) i) Evaporated milk is used for Ice cream manufacture. In preparation of bakery and confectionery products. In coffee and tea preparation. 49