In this article we will discuss about:- 1. Introduction and Development of Condensed Milk 2. Definition of Condensed Milk 3. Composition and Standards 4. Food and Nutritive Value 5. Physico-Chemical Properties 6. Role of Milk Constituents 7. Judging and Grading 8. Uses.
Introduction and Development of Condensed Milk:
The advent of condensed milks belongs to the nineteenth century. In 1809, Nicholas Appert (1749-1840), a French Food Scientist, announced his discovery of a means of preserving milk (without the admixture of sugar or other preservatives) by the following method- the milk was condensed by heating it in an open vessel placed in a water-bath over fire, to about two-thirds of its original volume.
The condensed milk was strained, cooled and poured into glass bottles, filling them to the brim and corking them tightly. The bottles so filled and sealed were then held in a boiling water-bath for two hours. The milk so treated was found to have very good keeping quality.
The commercially successful manufacture of condensed milk was initiated by the American, Gail Borden (1801-74), who is known as ‘the father of the process of milk condensing’. Borden is said to have experimented for some ten years before he finally decided that a semi-fluid state, produced by evaporation in vacuo, was the best form of preservation. In 1856, he received a patent both from the U.S.A. and England. Records show that Borden manufactured sweetened condensed milk sold under the famous Eagle Brand label as early as 1856.
About 1860, the Anglo-Swiss Condensed Milk Co. was organized in Switzerland by the American brothers Charles A. Page and George H. Page, with the assistance of Swiss and English capital. This company prospered and grew rapidly in Europe. About 1880, it extended its operations to the U.S.A., but in 1902 it sold its American interests to Borden. In 1904, it consolidated with Henry Nestle of Switzerland forming the Nestle-Anglo-Swiss Condensed Milk Co.
The basic principle in the process of preserving unsweetened condensed milk by heat-sterilization was introduced by John B. Meyenberg, a Swiss, who was an operator in the original plant of the Anglo-Swiss Condensed Milk Co., Switzerland. He migrated to the U.S.A. in 1884, and in the same year was granted a basic patent, on his invention of a sterilizer.
Later in 1884 and in 1887, he was granted patents on his process of preserving milk. His process patents provided sterilization by steam under pressure at a temperature not exceeding 116°C (240°F), while the sealed cans were continuously agitated by the revolving reel. This innovation provided the basis for a new industry.
The fundamental equipment used in the early days of the industry has not changed very much in principle. Condensation is still largely done in the vacuum pan or vacuum evaporator under the Gail Borden process, and sterilization is done by steam under pressure in sterilizers embracing the principles introduced by John B. Meyenberg.
In India, the Amul Dairy is credited with the first-ever commercial production of sweetened condensed milk under standard techniques, in 1961. The total annual production of sweetened condensed milk in 1974 was estimated at 6000 tonnes.
Definition of Condensed Milk:
Condensed milks are the products obtained by evaporating part of the water of whole milk, or fully 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’ respectively. 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 Rules (1976) the various condensed milks have been specified as follows:
Unsweetened condensed milk (evaporated milk) is the product obtained from cow or buffalo milk or a combination thereof, or from standardized milk, by the partial removal of water. It may contain added 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 additions need not be declared on the label. Unsweetened condensed milk should contain not less than 8.0 per cent milk fat, and not less than 26.0 per cent milk solids.
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 or orthophosphoric acid and polyphosphoric acid not exceeding 0.3 per cent by weight of the finished product.
Such additions need not be declared on the label. Sweetened condensed milk should contain not less than 9.0 per cent milk fat, not less than 31.0 per cent total milk solids and not less than 40.0 per cent cane sugar.
Unsweetened condensed skim milk (evaporated skimmed milk) is the product obtained from cow or buffalo skim milk or a combination thereof by the partial removal of water. It may contain added 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 additions need not be declared on the label. Unsweetened condensed skimmed milk should contain not less than 20.0 per cent total milk solids. The fat content should not exceed 0.5 per cent by weight.
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 additions need not be declared on the label. Sweetened condensed skimmed milk should contain not less than 26.0 per cent of total milk solids and not less than 40.0 per cent cane sugar. The fat content should not exceed 0.5 per cent by weight.
Composition and Standards of Condensed Milk:
(a) The gross composition of condensed milks, sweetened or unsweetened, whole or skim, is given in Table 8.1.
(b) The detailed composition of condensed milks is given in Table 8.2.
Note:
Composition of unsweetened milk has not been included, as this product is rarely manufactured.
(c) The Indian Standard specifications for sweetened condensed milks, whole or skim, are given in Table 8.3.
Food and Nutritive Value of Condensed and Evaporated Milks:
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 lactose. Further, while condensed milk is especially high in energy-giving sucrose, evaporated milk is suitable for infant feeding since it makes a soft curd which is easily digested.
Note:
There is some loss of vitamin B1 (30-50%) and vitamin C (60-100%) caused by sterilization in evaporated milk. However, milk is a poor source of vitamin C. Sterilization is reported to have a minor effect on the biological value and digestibility of milk-proteins.
Physico-Chemical Properties of Condensed Milk:
(a) 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. Table 8.4 gives some of the figures for specific gravity and Baume readings.
(b) Freezing Point:
The figures for condensed and evaporated milks are given in Table 8.5.
(c) Colour and Flavour:
The exposure to heat during manufacture and storage of condensed milks tends to darken their colour and develop a cooked flavour. The darkening of colour, commonly referred to as browning-discolouration, results from the interaction of the amino-compounds with sugar (principally casein with lactose) and has been called Maillard-type browning. The brown pigment is called melanoidin.
The cooked flavour is attributed to sulfhydryl compounds, which are formed during heat treatment. The rate of development and the intensity of these defects are cumulative. Further, the development of browning-discolouration is usually accompanied by the development of a cooked flavour, and vice versa. The above reactions also continue during storage.
The development of a brown colour in milk and milk products is objectionable. Although pasteurized milk exhibits no tendency to brown, certain condensed and dried milk products which are processed at high temperatures and stored at room temperatures for an appreciable time are subject to browning. Evaporated milk is particularly susceptible to this defect.
The principal factors affecting browning-discolouration and cooked flavour production in fluid milk systems are:
(i) Heat-Treatment:
Most important. The higher the intensity of heating, the greater the tendency for production of browning-discolouration and cooked flavour, and vice versa.
(ii) Total Solids Concentration:
The higher the concentration of milk solids (especially proteins and lactose) the greater the effect with any given level of heat-treatment, and vice versa.
(iii) pH:
The higher the pH (due to the increased level of added stabilizer) the greater the effect, and vice versa.
(iv) Storage Temperature and Time:
The higher the temperature and/or time of storage the greater the effect, and vice versa. (Refrigerated storage exhibits an inhibitory effect on colour development.)
(v) Oxygen Content:
The higher the oxygen content in the headspace of the container the greater the effect, and vice versa.
(vi) Various Added Compounds:
Reducing sugars (such as lactose and glucose) favour browning to a much greater extent than sucrose.
Note:
Besides amino-sugar or Maillard-type browning in milk and milk products, non-amino browning or caramelization occurs due to heat-decomposition of sugars in the absence of amino- compounds.
(d) Viscosity:
This refers to the resistance offered by a liquid to flow.
The viscosity of condensed/concentrated milks seems to be influenced by the following factors:
(i) Concentration:
The higher the degree of concentration of the milk solids the greater the viscosity, and vice versa.
(ii) Composition:
The higher the percentages of casein and fat (and also added sugar in the case of condensed milk) the higher the viscosity of condensed milks, and vice versa.
(iii) State of Protein and Fat:
The higher the instability of milk proteins (especially casein), the higher the viscosity upon heating, and vice versa.
(iv) pH and Salt-Balance:
The more disturbed the salt-balance (due to lower pH, as a result of developed acidity) the greater the viscosity, and vice versa.
(v) Temperature of Forewarming/Pre-Heating:
The lower the temperature the greater the viscosity, and vice versa.
Viscosity control during the manufacture and storage of condensed milks is highly important for successful marketing. To the trade and to the consumer, a viscosity sufficient to give the product a nice, full body symbolizes richness of milk. Neither an abnormally low (due perhaps to age-thinning) nor an excessively high viscosity (due perhaps to age-thickening) is desired.
Low viscosity suggests low nutritive value to the consumer; it also tends to leave an objectionable sugar sediment in condensed milk and fat separation in evaporated milk; excessive viscosity causes gel-formation and mineral deposit in evaporated milk.
Note:
Practically the same factors which control heat-stability during sterilization, also influence viscosity. However, the effect is in the opposite direction; in other words, an increase in heat-stability results in a decrease in viscosity, and vice versa.
Role of Milk Constituents in Condensed Milks:
(a) 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, tallowi- ness, etc.
(b) Milk-Proteins:
Technologically of great importance. Their physico-chemical reactions to processing-heat largely determine the heat-stability and viscosity of condensed milks.
(c) Milk-Sugar:
Plays an important role in the successful control of the texture of condensed milk. The size of lactose crystals determines the relative smoothness of condensed milk, and is controlled by the procedure used for the cooling and crystallization of this product.
(d) Mineral Salts:
These—particularly calcium and magnesium together with citrates and phosphates—control the salt-balance and heat-stability of milk. A disturbed salt-balance causes objectionable heat-coagulation of milk.
Judging and Grading of Condensed and Evaporated Milks:
Score Card:
This is given in Table 8.13 for condensed milk and Table 8.14 for evaporated milk.
Procedure for the Examination of Both Condensed and Evaporated Milks:
(a) Sampling:
Select a can of the product at random for examination.
(b) Sequence of Observations:
Avoid undue agitation when transporting the can 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 it in the following order:
(i) Appearance of the Can:
Look for signs of rust, etc., both outside and inside (when emptied).
(ii) 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.
(iii) Viscosity (Body and Texture):
Observe whether the viscosity is high, normal or low while pouring the contents into a beaker.
(iv) Sediment:
Watch for presence and absence of sediment at the bottom of the container when emptied.
(v) Flavour and Odour:
Note defects, if any, by placing a small spoonful of condensed milk or of diluted evaporated milk (1:1 with distilled water) on the tongue.
(vi) Laboratory Tests:
Take a suitable sample aseptically and then test for fat, total solids, bacteria, sugar, adulterants and preservatives, etc.
(c) Requirements of High Grade Condensed and Evaporated Milks:
High quality condensed milk should have a clean, pleasant aroma, & pronounced sweet taste, smooth and uniform body and texture, and a uniform light colour, which should be yellow for cow and light- greenish white for buffalo milk. High quality evaporated milk should have a mild, pleasant flavour, a relatively viscous body and uniformly smooth texture, and uniform colour.
Uses of Condensed and Evaporated Milks:
Condensed Milk:
(i) For reconstitution into sweet milk drinks;
(ii) In tea or coffee;
(iii) In ice cream preparation;
(iv) In candy and confectionary;
(v) In prepared foods.
Evaporated Milk:
(i) For reconstitution into milk for feeding infants and persons with weak stomachs, etc.;
(ii) In ice cream;
(iii) In tea and coffee.
Plain Condensed Milk:
This is unsweetened condensed milk, made from whole milk, partly skim milk or entirely skim milk, and condensed to 2.5 to 4:1. It is used in ice cream factories and bakeries. The product is neither sterile nor preserved by sugar. Its keeping quality is similar to that of high quality, efficiently pasteurized milk.
Superheated Condensed Milk:
This is plain condensed milk superheated by blowing live steam towards the end of the condensing period. The major purpose of superheating is to increase the viscosity. It is used in ice cream factories and bakeries, where it is believed to yield better results than plain condensed milk.
Frozen Condensed Milk:
This is plain condensed milk frozen to give it longer storage life. It is used largely in ice cream factories.