Milk is a liquid and therefore requires a container at every stage of movement from the cow to the consumer. At the early stages of dairy development the cow's udder was used as the basic container for all purposes. The cow, kept in the town stall, was brought to the customer's doorstep for milking. In some cases the milk was sold from a shop adjacent to the cowshed. In many European countries town cow-keepers could still be found after the first world war but, for reasons of hygiene and economy, they quickly disappeared. This trend seems to be unavoidable for the dairy industry worldwide and will certainly be applied to cities in developing countries where town cow-keeping still exists.
The growing demand for milk in towns and the high costs of milk production within their boundaries led to the development - probably around 1860–70 - of containers suitable for various stages of marketing and distribution. These were metal cans, provided with a lid and having capacities up to about 80 litres. The introduction of this type of container (until recent years often called a ‘churn’) facilitated the transport by railway from rural areas to towns, thus contributing substantially to the rapid growth of milk distribution. Similar containers were also used for retail delivery to the consumer, the milk being dispensed in the street or at the doorstep into the consumer's container.
The first significant development in the packaging of milk for retail sale came at the very end of last century with the introduction of the process for sterilized milk in which the retail container, the glass bottle, formed an integral and essential part. In the third decade of this century bottling of pasteurized milk developed rapidly, first in America and soon after in Europe. The glass bottle as the retail package for milk remained unchallenged until 1933 when the first carton made of waxed paper was introduced. The development and introduction of plastic materials for packaging in the dairy industry (initially polyethylene in 1940), alone and in combination with paper, resulted in a wide range of containers, termed cartons, suitable for liquid milk.
When we refer to liquid milk we usually mean a product, either processed or, less often, sold raw to the consumer, deriving from a lactating ruminant, mainly the cow. Processing depends on the grade of milk to be manufactured following the regulations and customs of the country. Heat treatment and, in most countries, standardization of butterfat content, are the basic parts of the processing procedures.
Heat treatment may be classified as:
sterilization (in bottle)
UHT (ultra-high-temperature) treatment integrated with aseptic packing.
Pasteurization HTST (high-temperature short-time - heating at 72°C for 15 seconds) fulfils the following main objectives:
to safeguard public health by destroying all pathogenic bacteria
to extend the keeping quality of liquid milk by destroying most of the milk-souring micro-organisms
to ensure a product with a good keeping quality.
Sterilization (in bottle) is the term applied to a heat treatment process which has a bactericidal effect greater than pasteurization. Although it does not result in sterility, it gives the processed milk a longer shelf life. This is achieved partly by using a more severe heat treatment (about 110°C for 20–30 min) and partly by applying the treatment after the bottle is filled and sealed which eliminates the risk of contamination during packaging. As a result of the long holding time at this elevated temperature, the product has a cooked flavour and a pronounced brown colour.
UHT treatment is a process of high bactericidal effect, developed as a continuous flow process in which the milk is heated at 135°C–150°C for about two seconds only. This treatment must be integrated with aseptic packaging in sterile containers. UHT milk has less pronounced cooked flavour and no brown colour.
As a criterion for packaging requirements for pasteurized milk in general, a shelf life of several days at a temperature below 10°C can be assumed. In-bottle sterilized milk can normally be kept for weeks and UHT milk aseptically packaged can be kept for several months, both without refrigeration, provided the package is not opened. After opening, the sterility of the product is lost and the shelf life becomes close to that of pasteurized milk.
Sales of unpasteurized milk are rare in countries with a developed dairy industry and often prohibited by law. Nevertheless, there are some where purchased milk is boiled at home as a common habit even though the raw milk is of a high hygienic standard. In such cases heat treatment in the milk plant may be considered as an unnecessary expense and not required by law. This is the case in Switzerland, although even there in recent years the share of heat treated milk in the total sales is increasing. Fig. 1 and 2 show the relevant trends in Switzerland and in Western Europe as a whole.
Fig. 1 Distribution of liquid milk in Switzerland
Fig. 2 Packaged milk in Western Europe
From this brief survey of heat treatment methods for liquid milk it becomes evident that the sterilized and UHT milks are commodities which by their very nature must be distributed to the consumer as a packaged product. Pasteurized milk, however, which is normally required to have a shelf life, under refrigeration, of only a few days can be distributed in wholesale quantities provided the necessary care is taken to prevent contamination.
The type of liquid milk produced and the consequent selection of a packaging and distribution system constitutes in many instances an extremely intricate optimizing problem. The selection will have to satisfy the requirements dictated by existing economic limits, production and distribution efficiency, retailing objectives, consumer considerations and ecological aspects.
Even when the decision on the packaging system has been well founded and made with due consideration to all relevant demands, the actual application may sometimes prove to be a failure for lack of competent supervision of its application.
For the purpose of this study the classification of processing and distribution systems of liquid milk - as in use at present - is shown in Table 1.
Table 1. Classification of packaging and distribution systems
|Liquid milk||Returnable containers||Single service containers||Despatch by tankers to vending machines|
|Glass bottles||Plastic bottles||Cans||Cartons||Sachets||Plastic bottles||Bag in box|
The seven systems marked with asterisks have been chosen for a more detailed study in this publication. Returnable and single-service plastic bottles have not been included since they are mainly suitable for larger capacities of milk plants. Plastic bottles are normally used as single-service containers. They are usually blow-moulded from polyethylene which is often a mixture of high and low density grades. Occasionally polystyrene is used. The basic advantage of plastic bottles in comparison with glass is the lower weight of the former (about one-twentieth that of glass).
The bag-in-box system is intended primarily for milk supplies to catering establishments and has not found application to general milk distribution. Aseptic packaging of UHT treated milk in plastic sachets has not been included as this is still in the process of development and must be considered in conjunction with the UHT processing equipment employed. The extra cost of aseptic sachet packaging equipment compared with that for pasteurized milk can be assumed to be in a similar proportion as that for aseptic and normal carton machines. It should be mentioned that a promising UHT system with aseptic filling into plastic sachets is being developed in Finland with electric heating of the milk. Commercial trials are under way.
The sale of milk in bulk through automatic vending machines has been introduced in Mexico and India and seems to be an important innovation in milk packaging and distribution systems. A description of this system is given in Chapter 7.
In presenting data relating to the operations of the liquid milk packaging division of a milk plant, transport from the plant to retail outlets and retail systems it has been assumed that milk reception, raw milk storage, standardization, homogenization, pasteurization and bulk storage of milk after pasteurization are common for all systems. Packaging operations therefore begin at the outlet of pasteurized milk tanks. It is assumed that pasteurized chilled milk is used for UHT treatment and sterilization, homogenization (which is not always necessary) is a part of pasteurized milk processing, while storage tank types and capacities are considered as uniform though they may differ in practice. In spite of this, data resulting from this analysis can be considered as comparable within a reasonable margin of error.
Fig. 3 illustrates the seven liquid milk packaging systems analysed in this publication. The common divisions of a liquid milk plant also shown in the diagram (two types of reception, recombination, pre-treatment and storage of pre-treated milk) are not included in the subsequent analysis.
Fig. 3 Selected liquid milk processing systems
Techno-economic evaluation of the systems necessitates consideration of the following essential items:
packaging materials and storage systems
machinery, equipment and area requirements in the plant
requirement of services
transport to the retailer
costs and losses of packaging material and losses of milk.
These components may be considered as basic elements of what may be called divisional costs of liquid milk packaging and distribution within the definitions and limitations described above and are, therefore, a fair indication of the cost differences between the various systems.
In order to arrive at the fullest possible comparability of data, this analysis has been made for one size of package, i.e. half-litre, which is probably the most common size used in developing countries; some data are also provided for units of one litre.
Specific technical requirements for a dairy enterprise often depend on the capacity of the milk plant. For instance, the specific area for milk processing (m2/1 000 litres) will be smaller in a 100 000 litres/day plant than in a 10 000 litres/day plant. It has been necessary, therefore, to relate the particular specific requirements to the capacity, and for this purpose five capacities have been selected, namely 10 000 litres/day, 25 000 litres/day, 50 000 litres/day, 100 000 litres/day and 250 000 litres/day. Below 10 000 litres/day a milk plant can hardly be considered as a commercial enterprise: on the other hand, in the range of capacities between 100 000 litres/day and 250 000 litres/day the specific requirements of most components become constant and continue beyond the 250 000 litres/day point. Diagrams have been used to illustrate the results, as this appeared to be the most comprehensive method of presentation.
Several assumptions concerning working time, efficiency coefficients, routeing of vehicles, etc. have had to be made. As far as feasible, they have been considered as uniform for all systems. Their values have been compared with and adjusted to real figures available from existing plants, particularly in developing countries. All factors taken into consideration in this respect are explained in the paragraphs concerned.
Specifications for basic machinery and equipment depend on the daily throughout of the division, the efficiency with which machines are utilized and on the operations in the storage and distribution rooms. In smaller units the degree of mechanization has been limited to basic functions of the plant. In larger units operations related to storage and dispatch of the product, as well as those connected with the reception of returnable empties (crates, bottles, cans) have been considered as justifying mechanization. The equipment listed would be usually recommended when establishing a new liquid milk packaging division. It has been assumed that, according to the practice of the majority of milk plants, the division operates two eight-hour shifts daily.
A cost evaluation of the systems, valid for developing countries all over the world, is not a feasible task. Therefore, it seemed appropriate to express first the magnitudes of the various components in physical units (m2, kg, hours, etc) as specific values, i.e. related to 1 000 litres of milk distributed. However, a conclusive techno-economical comparison of different systems is not possible when different components cannot be added together, for instance if one component is expressed in m2/1 000 litres and the other in kgh/1 000 litres. The only common measure for all components is a currency unit, but this implies application of selected uniform rates for different expenditures (machines, construction, labour, fuel, materials, etc) and there is no uniformity of such costs all over the world. Nevertheless, an attempt has been made to assess and compare the specific divisional costs by applying uniform rates in US currency to the various cost components. They should be considered as figures indicating basically the relations between different components, and not necessarily as reflecting precisely the real costs of any given project. In order to arrive at estimates of actual costs the methods of calculation given can be applied, but actual rates should be used.
Details of relevant technologies and machines are limited in this analysis to the necessary minimum, since they can be found in specialized publications.
There are numerous different designs of machines and kinds of packaging material for liquid milk packaging on the market. With very few exceptions, the equipment and packaging material for each of the systems are produced by a number of companies. They differ in design, capacities, weight, dimensions, etc., but many of them fulfil equally well the hygienic, technical and economic requirements for use in modern dairying. In this study only one example of each system analysed could be chosen. The companies which have collaborated with FAO by providing information and technical material for this publication are listed on p. 80. The author emphasizes the non-promotional and non-discriminatory nature of this list.