The unit should be located as centrally as possible within a given milk-producing area, near a source of water, or in a place where water is available. The site should be cool and well-ventilated. Sometimes not all these conditions can be met. The most important factor is availability of water. It should be remembered that on average five litres of water are required to process one litre of milk.
Milk and dairy products are biologically active substances which are influenced by their environment. Cheese quality and reliability depend largely on the surroundings in which cheese is manufactured. An unused building can be purchased or leased and adapted for milk processing operations, or a new building can be constructed. It is not uncommon to find in some remote milk-producing areas, abandoned milk collection centres which may be suitable.
For a new building, the following factors should be taken into consideration:
the walls should be built of local stone and the inner walls lined with a lime-cement mixture for easy cleaning;
the cement floor should have a 2 to 3 percent slope for draining water used in cleaning;
windows should be sufficient to provide adequate ventilation.
For village cheese manufacture, the second component of the building is the ripening cellar.
The most important features of a ripening cellar are maximum moisture (80 percent relative humidity) and low temperature (8 to 12°C). To achieve or approach these standards, a room partly below ground level is recommended. It should be about 2.5 m high. The floor of the room should be dug to a level of some 1.5 m below ground, with windows or openings made in the upper walls to lower the temperature of the cellar by a circulating draught, particularly important during the night.
Building size will of course depend on the quantity of milk received during the peak production period. An average quantity of milk which can be processed by a small-scale unit amounts to 100 to 500 litres per day. For these quantities the building area should be some 50 sq. m.
Section of the processing unit
Diagram of building layout
Sectional diagram of processing unit and equipment
As previously pointed out, milk processing operations will take place far from urban consumption centres. In these areas the quantities of milk hardly exceed an average of 500 litres per day.
The products made must be able to withstand long periods of transportation, often under difficult climatic conditions.
Milk products can be processed as illustrated:
Butter, cheese and processed cheese may require lengthy transportation, given the distance from consumer centres, whereas buttermilk and yoghurt can be marketed in the vicinity of the processing unit. The whey will be returned to the dairy farmers.
The main steps in obtaining the above products are:
Standardization: Standardization is an operation producing milk with a constant butterfat content through partial, manual skimming. The operation makes it possible to standardize the composition of the finished product and to set aside part of the cream for butter.
Heat treatment: Pathogenic germs in milk are destroyed by heating the milk to a minimum temperature of 63°C for 30 minutes.
Inoculation: Due to heat treatment, which destroys a large number of lactic bacteria, cheese or yoghurt-making requires the addition of lactic bacteria to the milk. These bacteria are selected according to the type of finished product required.
Clotting: Milk changes from a liquid to a solid state through the use of a coagulant: rennet.
Curd-Separation: In cheese-making, the milk after coagulation is cut and separated into a liquid whey, and cheese curd.
Ripening: This phase of cheese-making allows cheese texture to become homogeneous and the aroma to develop.
Churning: In this operation, cream is churned to produce a semi-solid product which becomes butter.
Melting and emulsification: Defective cheeses are melted and emulsified with salts to obtain a solid consistency and, after cooling forms processed cheese.
In addition to the eight steps mentioned above, milk collection, milk analyses and the marketing of the finished products should be equally regarded as important operations.
Each one of these important operations is described in the following chapter according to the five traditional operations: reception, standardization, processing, storage and distribution.
The equipment needed to run the dairy processing plant depends on several factors: how much milk is to be collected, how far and how scattered are the milk producers, what kind of product is to be produced?
In the standard milk processing pattern, commencing with milk collection and ending with the sale of the dairy products, the following equipment would normally be required:
Plastic milking pails are often an improvement on the utensils commonly used.
The producer should use small aluminium milk cans of 5–10 litre capacity for transporting the milk, while the collector should use 30–50 litre cans.
If the milk needs to be collected, the following will be needed: the use of a bicycle, a 50 litre milk can, a graduated cylinder lacto-densitometer and a measuring pail.
The amount and density of the milk collected from each producer should be entered in a notebook. The following is a sample entry:
|No.||Name of producer||Amount delivered (litres)||Density||Signature|
Reception: the following equipment is needed for the reception of milk brought in by producers themselves and by the collector: a milk scale and a pail.
Storage: a milk funnel and 50 litre milk cans.
Standardization/Cream separation: a manual cream separator has to be used to skim a portion of the milk received.
|Milk scale and pail||milk funnels filter and milk can||Standardization hand-operated separator|
Heat treatment: there are several possibilities for heat treatment, depending on the available power source. Under the least favourable circumstances, the sole available energy source is wood or peat. The best thing to use in this case is a “boiler/water bath” as in the model below:
More elaborate models can be built for wood or gas-fuelled heating (where bottled gas is available).
|Wood-fuelled metal boiler||Gas-fuelled metal boiler|
For 100–500 litre quantities of milk, milk pasteurization with a plate pasteurizer is not recommended.
Cooling: the milk is cooled with running water in a vat:
Simple cooling vat
or by water circulating in a jacketed vat.
Jacketed cooling vat
Clotting: The cheese vat can be of aluminium with a tap for draining the whey.
Simple milk clotting vat
A jacketed vat can also be used for milk clotting.
jacketed clotting vat
There are other possible types of cheese vats, depending on the resources available to dairy producers. The following are a few examples:
simple vat to process 50–100 litres of milk
Low-walled clotting vat
a more elaborate vat for processing 100–300 litres of milk: milk cooled by cold water circulating within its jacket:
Clotting vat equipped for cooling
for larger amounts of milk up to 500 litres, a vat equipped for heat treatment, cooling and clotting can be designed as shown in the following diagram:
Draining: the cheese is drained in moulds set on a slanting surface to drain the whey. The moulds, which give the cheeses their characteristic shapes, vary greatly in size and form.
The simplest way to make cheese moulds is to cut a plastic pipe generally used for drainage into 10 cm sections.
The resulting cylinders are perforated as in the model below:
Bases and Lids are of wooden discs slightly smaller in diameter than the cylinders.
Moulds with bases and Lids
Cheese moulds may also be made of wood, their shape varying according to the type of cheese made.
The cheese-draining table, slanted forwards to facilitate draining of the whey, is made of wood.
Wooden cheese-draining table
Pressing: different kinds of cheese (curd) presses can be made. The simplest press is made by placing weights or cement block on the moulded cheese (curd) as shown in the following diagram:
Other presses can be constructed according to the following designs:
|Vertical screw press|
Ripening: wooden shelves must be assembled for the cheese-ripening cellar.
Marketing, as previously mentioned, is a very important aspect of overall operations. Quality of presentation is important. Wooden boxes made to accommodate the specific cheese shapes are used to transport the cheese to consumer areas.
Wooden cheese boxes
An important component in a dairy processing unit, is the laboratory.
Laboratory equipment should include the following:
To measure milk density:
Two or three lactodensitometers with glass cylinders
To test milk acidity:
A Dornic acidimeter and the accessories shown below.
Salut acidimeter used for selective testing of milk acidity immediately after reception of farmers' milk
• Fat content of milk
• Preparation of cultures
To prepare mesophilic cultures for cheese-making or thermophilic cultures for yoghurt-making, a strain of starter culture is initially required. Culturing and sub-culturing is done in individual 5, 10 and 15 litre containers.