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Condensed milks are the milks obtained by evaporating part of water of whole milk, orfully or partly skimmed milk, with or without the addition of sugar. The term ‘condensed milk’ is commonly used when referring to “full cream sweetened condensed milk” while the term evaporated milk is commonly used when referring to ‘full cream unsweetened condensed milk’. Skimmed milk products are known as “sweetened condensed skim milk” and “unsweetened condensed skim milk”. The ratio of concentration of milk solids is about 1: 2.5 for full cream products and 1: 3 for sweetened condensed skim milk.
According to the PFA (1976) the various condensed milks have been specified as follows:
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Unsweetened condensed milk (evaporated milk) is the product obtained from cow or buffalo milk or a combination therefore, or from standardized milk, by the partial removal of water. It may contain added calcium chloride, citric acid and sodium citrate, sodium salts oforthophosphoric acid and polyphosphoric acid not exceeding 0.3 per cent by weight of the finished product. Such addition need not be declared on the label. Unsweetened condensed milk should contain not less than 8.0 percent milkfat, and not less than 26 per cent milk solids.
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Sweetened condensed milk is the product obtained from cow or buffalo milk or a combination thereof, or from standardized milk, by the partial removal of water and after addition of cane sugar. It may contain added refined lactose, calcium chloride, citric acid and sodium citrate, sodium salts of ortho phosphoric acid and poly phosphoric acid not exceeding 0.3 per cent by weight of the finished product. Such addition need not be declared on the label. Sweetened condensed milk should contain not less than 9.0 percent milk fat, and not less than 31 per cent milk solids and40.0 per cent cane sugar.
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Unsweetened condensed skim milk (evaporated skimmed milk) is the product obtained from cow or buffalo milk or a combination thereof, by partial removal of water. It may contain added calcium chloride, citric acid and sodium citrate, sodium salts of ortho phosphoric acid and poly phosphoric acid not exceeding 0.3 per cent by weight of the finished product. Such addition need not be declared on the label. Unsweetened condensed skim milk should contain not less than 20.0 percent total milk solids. The fat content should not exceed 0.5 per cent by weight.
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Sweetened condensed skim milk is the product obtained from cow or buffalo skimmed milk or a combination thereof by the partial removal of water and after addition of cane sugar. It may contain added refined lactose, calcium chloride, citric acid and sodium citrate, sodium salts of orthophosphoric acid and polyphosphoric acid not exceeding 0.3 per cent by weight of the finished product. Such addition need not be declared on the label. Unsweetened condensed skim milk should contain not less than 26.0 per cent total milk solids and not less than 40 per cent cane sugar. The fat content should not exceed 0.5 percent by weight.
Detailed Composition of the condensed milk (percentage)
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Type of condensed milk
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Water
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Total solids
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Fat
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Milk solids not Fat
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Protein
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Lactose
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Ash
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Total milk solid
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Sucrose
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Condensed milk
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26.0
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74.0
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9.0
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22.0
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8.3
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12.2
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1.5
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31.0
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43.0
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Evaporated milk
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31.0
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69.0
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9.0
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22.0
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8.3
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12.2
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1.5
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31.0
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-
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Skim sweetened
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29.0
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71.0
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0.5
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25.5
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9.3
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14.0
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2.2
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26.0
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45.0
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Indian Standard Specifications for condensed milk
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Characteristics
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Requirement for
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Condensed milk
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Skim sweetened
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Total milk solids (%wt.) Min
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31.0
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26.0
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Fat (% wt)
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Not less than 9.0
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Not more than 0.5 %
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Sucrose (% wt.) Min
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40
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40
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Acidity(% lactic) Max
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0.35
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0.35
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Bacterial count (per g.)
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500
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500
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Coliform count (per g)
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Negative
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Negative
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Yeast and mould count (per g.) Max
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10
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10
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Food and Nutritive value of condensed and evaporated a milk
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Both have high nutritive value, both are rich in fat and fat-soluble vitamins A, D E and K, body building proteins, bone forming minerals and energy-giving sucrose,evaporated milk is suitable for infant feeding since it makes a soft curd which is easily digested.
Physico-chemical properties
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Specific gravity/density: Evaporation of water in the manufacture of condensed milks raises their specific gravity/density, which is universally employed to control their composition. Baume hydrometers are widely used for this purpose.
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Freeing point: The freezing point of condensed milk is –14.9ºC and that of evaporated milk is - 1.3ºc
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Colour and flavour: Heat treatment during manufacture of condensed milks tend to darken their color and develop cooked flavour, the darkening/browning-discoloration results from the interaction of the amino-compounds with sugar (casein and lactose) and is called as Maillard-type browning. The brown pigment is called as melanoidin.
Role of Milk constituents in condensed milk
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Milk fat: Imparts a rich and pleasing flavour,soft body and smooth texture to both condensed and evaporated milks. Affects viscosity. Significant in flavour problems, such as rancidity, tallowiness, etc.
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Milk-Proteins: Technologically of great importance and their physico-chemical reactions to processing-heat largely determine the heat stability and viscosity of the condensed milks.
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Milk sugar: Plays an important role in the successful control of the texture of condensed milk. The size of the lactose crystals determines the relative smoothness of the condensed milk, and is controlled by the procedure used for the cooling and crystallization of this product.
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Mineral salts: These-particularly calcium and magnesium together with citrates and phosphates control the salt balances and heat stability of milk. A disturbed salt-balance causes objectionable heat-coagulation of milk.
Method of manufacture, packaging and storage of condensed milk
Receiving milk
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Filtration /Clarification (38-40ºC)
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Standardization
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Fore warming/preheating (115-118 ºC / No Hold)
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Condensing (2.5:1)
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Addition of sugar
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Homogenization
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Quickly cooled to 30ºC
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Seeded with 0.1 - 0.3% lactose
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Vigorous stirring and slow cooling for 1 hour.
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Temperature of 15 ºc reached
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Stirring continued until packed.
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Storage at 10 ºc.
Details of manufacture
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The basic principle in the production of condensed milk and evaporated milk is that high quality milk is filtered /clarified, standardized, fore-warmed and condensed /evaporated to the desired level. The concentrated product is preserved by the addition of sugar for condensed milk and by heat sterilization for evaporated milk.
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When the milk is received at the plant, its temperature should be at 10ºC or below. The milk should be clean, sweet, and free from off-flavours and odours and reasonably free form extraneous material.Contamination by antibiotics, pesticides and other chemical residues and metals is highly undesirable; abnormal milk should not be accepted. Acid development is objectionable for not only does this indicate an excessive bacterial count,but it also reduces the heat stability of milk.
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The various platform tests and laboratory tests usually performed on the intake milk to determine its acceptance /rejection are
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Alcohol test
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Clot on boiling tests.
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Alcohol test: To make this test, 5 ml of milk is placed in a test tube and an equal amount of solution with 68 % alcohol added,the mixture is shaken and any formation of clot or flake denotes a positive test, i.e., the milk is susceptible to heat coagulation. A disturbed salt balance affects alcohol coagulation in the same manner as heat coagulation. The test detects: abnormal milk including colostrum. Which is high in mineral salts and developed acidity in milk,mastitis milk likely to result in sweet curdling etc., It is more sensitive than the COB test.
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Alcohol index : determined by placing absolute alcohol in the burette and 10 ml of milk in a beaker. The number of ml of alcohol required for flake formation is known as the Alcohol Index (AI). An AI of 7 is indicative of good stable milk for acceptance, while 3 or less shows that the milk is fit for rejection.
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Alcohol alizarin test: This test not only determines the heat stability of milk but also the pH.
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Clot on boiling test : In this test, 5 ml of milk is placed in a test tube and kept in a boiling water bath for 5 minutes, afterwards it is removed and examined for precipitation, if curd is observed, the milk is said to fail the COB test and should be rejected.
Filtration/clarification
Standardization
Standardization of the raw milk is carried out in 3 stages, for
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The first standardization which establishes the desired fat / SNF ratio (usually 1:2.44, done in raw milk))
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The second, which establishes the desired ratio of added sugar to the total milk solids (done prior to condensing)
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The third, which adjust the concentration of the finished product to the required, total solids Content(after finishing the batch, i.e., prior to homogenization)
Forewarming / Pre-heating
Addition of sugar
Amount of sugar to be added
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This ranges from 40-45 % in the finished product, which requires 18-20 percent sugar on milk basis. As per Hunziker, (scientist), advocated a sugar ratio (sugar-in –water concentration) of62.5 to 64.5 per cent. Sugar Ratio Determination (SR). This can be calculated either by using
( % SR = %sugar / % sugar + %water ) X 100
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