29 May - 28 July, 2000
E-mail conference on
Discussion Paper 1.2:
Issues raised by the conference moderators:
The following paper mainly addresses the situation in medium to larger scale milk collection and transport systems. It is being issued along with a poster paper on the Lactoperoxidase System (LP-s) of Milk Preservation.
Remember, the definitions of small scale collection and processing for the purposes of the email conference are:
Participants may wish to
send in their own specific experiences on small scale milk collection,
preservation and transport. With this request in mind, the moderators
would like to ask the following questions:
1. The LP system is just one alternative to refrigeration in small scale situations. Do you know of other alternative systems or technologies that are efficient and cost effective? Systems that use, for example, solar powered refrigeration, or absorption refrigeration, or ....................... ?
2. What does it cost, in US cents, a small scale dairy enterprise in your area/enterprise/country to collect one litre of raw milk (from farm to processing unit)? How does this compare with say, the ex-factory price of one litre of pre-packed pasteurised milk.? How can these costs be kept to a minimum?
Discussion paper 1.2: Milk Collection, Preservation and Transport
By: Jose Pedro Urraburu, Manager,
Pan American Dairy Information System (INFOLECHE), a service of the Pan
American Dairy Federation (FEPALE), Montevideo, Uraguay.
1. Machine milking
On medium to large dairy farms, the usual practice is to milk cows by a milking machine that sucks the milk out of the teat by vacuum. The milking equipment consists of a vacuum pump, a vacuum vessel which also serves as a milk collecting pail, teat cups connected by hoses to the vacuum vessel, and a pulsator which alternately applies vacuum and atmospheric pressure to the teat cups.
The teat cup unit consists of a rigid outer case containing an inner tube of rubber, called the teat cup liner. The inside of the liner, in contact with the teat, is subjected to a constant vacuum of about 0.5 bar (50% vacuum) during milking. The pressure in the pulsation chamber (between the liner and teat cup) is regularly alternated by the pulsator between 0.5 bar during the suction phase and atmospheric pressure during the massage phase. The result is that milk is sucked from the teat cistern during the suction phase. During the massage phase the teat cup liner is pressed together to stop milk suction, allowing a period of teat massage and for new milk to run down into the teat cistern from the udder cistern. This is followed by another suction phase, and so on.
Relaxation of the teat during the massage
phase is necessary to avoid accumulation of blood and fluid in the teat,
which is painful to the cow and will cause her to stop letting down.
The pulsator alternates between the suction and massage phases 40 to 60 times
To eliminate the heavy and time-consuming
work of carrying filled pails to the milk room, a pipeline system may be
installed for direct transport of the milk to the milk room by vacuum. Such
systems are widely employed on medium sized and large farms and allow milk to
be conveyed in a closed system straight from the cow to a collecting tank in
the milk room. This is a great advantage from the bacteriological point
of view. It is however important that the pipeline system is designed to
prevent air leakage agitating the milk in a harmful way. The machine
milking plant is also provided with cleaning-in-place (CIP) facilities.
2. Chilling milk on the farm
Milk leaves the udder at a temperature of about 37C. Fresh milk from a healthy cow is practically free from bacteria, but must be protected against infection as soon as it leaves the udder. Micro-organisms capable of spoiling the milk are everywhere - on the udder, on the milker's hands, on air-borne dust particles and water droplets, on straw and chaff, on the cow's hair and in the soil. Milk contaminated in this way must be filtered.
Careful attention must be paid to hygiene in order to produce milk of high bacteriological quality. However, despite all precautions, it is impossible to completely exclude bacteria from milk. Milk is in fact an excellent growth medium for bacteria - it contains all the nutrients they need. So as soon as bacteria get into milk they start to multiply. On the other hand, the milk leaving the teats contains certain original bactericides which protect the milk against the action of micro-organisms during the initial period. It also takes some time for infecting micro-organisms to adapt to the new medium before they can begin to grow.
Unless the milk is chilled it will be quickly spoiled by micro-organisms, which thrive and multiply most vigorously at temperatures around 37oC. Milk should therefore be chilled quickly to about 4oC immediately after it leaves the cow. At this temperature the level of activity of micro-organisms is very low. But the bacteria will start to multiply again if the temperature is allowed to rise during storage. It is therefore important to keep the milk well chilled.
Under certain circumstances, e.g. when
water and/or electricity is not available on the farm or when the quantity of
milk is too small to justify the investment needed on the farm, co-operative
milk collecting centres should be established.
3. Farm cooling equipment
Spray or immersion coolers are used on farms which deliver milk to the dairy in cans. In the spray cooler, circulating chilled water is sprayed on the outsides of the cans to keep the milk cool. The immersion cooler consists of a coil which is lowered into the can. Chilled water is circulated through the coil to keep the milk at the required temperature.
Where milking machines are used, the milk is collected in special farm tanks. These come in a variety of sizes with built-in cooling equipment designed to guarantee chilling to a specified temperature within a specified time. These tanks are also often equipped for automatic cleaning to ensure a uniformly high standard of hygiene.
On very large farms, and in collecting
centres where large volumes of milk (more than 5 000 litres) must be chilled
quickly from 37oC to 4oC, the cooling equipment in the bulk tanks is
inadequate. In these cases the tank is mainly used to maintain the
required storage temperature; a major part of the cooling is carried out in
in-line heat exchangers in the delivery pipeline.
4. Frequency of delivery to the dairy
In former times milk was delivered to the dairy twice a day, morning and evening. In those days the dairy was close to the farm. But as dairies became larger and fewer, their catchment areas grew wider and the average distance from farm to dairy increased. This meant longer intervals between collections. Collection on alternate days is now common practice, and collection every three or even four days is not entirely unknown.
Milk should preferably be handled in a closed system to minimise the risk of infection. It must be chilled quickly to 4oC as soon as it is produced and then kept at that temperature until processed. All equipment coming into contact with milk must be cleaned and disinfected.
Quality problems may arise if the
intervals between collections are too long. Certain types of
micro-organisms, known as psychrotrophic, can grow and reproduce below
+7oC. They occur mainly in soil and water, so it is important that
water used for cleaning is of high bacteriological quality. After an
acclimatisation period of 48-72 hours, growth goes into an intense
logarithmic phase. This results in breakdown of both fat and protein, giving
the milk off-flavours that may jeopardise the quality of products made from
it. This phenomenon must be allowed for in planning of collection
schedules. If long intervals cannot be avoided, it is advisable to chill the
milk to 2-3oC.
5. Milk transportation to the dairy
The tanker driver who comes to the farm or the co-operative milk collecting centre to pick up the milk, should take a representative sample and preserve it properly it to maintain the same properties from the time it was taken, until it is received at the dairy. The same principle applies to the collected milk, which should be transported in an insulated tank capable of maintaining a temperature between 4ºC and 9ºC.
Drivers must follow regular routines to
transport milk from the farm to the dairy as follows:
thermographs measure temperature levels of the milk. In advanced dairy
countries, the insulated trucks are equipped with automatic sampling devices.
Prices for these devices range from US$ 500 to US$ 7,000.
6. Control software
Some available software products allow the
dairy to keep record of the complete milk transportation chain: milk samples,
driver and tanker tracking, shipment volumes, etc.
7. Case study: a Brazilian dairy co-operative
Contrary to the notion that the small dairy farmer is destined to failure, the Co-operative Agropecuaria de Boa Esperança Ltda. (CAPEBE), located in Minas Gerais, Brazil has successfully developed a milk collection programme among its farmers, 80% of them producing an average of 100 litres/day. The key of the programme is the common cooling tank.
After more than a year of the new collection programme implementation, the region of Esperança where CAPABE operates has nine common cooling tanks working, and four more in the process of installation.
Between April 1999 and February 2000 CAPEBE bulk milk collection, including 55 private cooling tanks, has grown from 28% to 70% of its 55,000 litres/day production. This has allowed CAPEBE to reduce milk rejected at reception from 140,000 litres in 1997 to 16,400 litres in 1999.
One of the major impacts of the programme on dairy farmers was the dramatic reduction of transport costs, which in some regions fell up to 80%. For example, in some places, the transport cost per litre went down from US$ 0.022 to US$ 0.007 per litre.
Before the use of common cooling tanks, the tanker would travel a distance of 90 kms, loading between 1,000 and 1,200 litres per day. Today, after two common tanks and five private tanks have been installed, the tanker circuit is down to 58 kms., loading 6,500 litres of milk every two days. In addition to the reduced transportation costs, product quality has improved because the time between milking and arrival at the dairy has been significantly reduced.
At a price of US$ 5,155, each cooling tank has a capacity to store 2.500 litres of milk. The farmers use the financing offered by CAPEBE that allows payments in 15 months without interests, five months more than the market financing. The tank invoice goes to one of the associated farmers, but all of the farmers authorise CAPEBE to discount the payments from their milk cheques.
The most recent purchase of a common
cooling tank was made in March of this year, by 16 dairy farmers who together
produce 1.200 litres/day.
Appendix 1: Cooling tanks prices
Here are some reference prices for
different capacity cooling tanks, available in the Brazilian market (May
Milking machines and milk cans prices
The following are reference prices of milk
cans available in the Brazilian market, and milking machines available in
Milk cans and pails – May 2000
Milking machines – December 1999
Appendix 2: Farm equipment sources
The following are a few examples of farm and testing equipment manufacturers:
– Farm Equipment (Germany)
Complete lists of companies in Latin
America can be purchased at the Pan American Dairy Information System -