Traditional Cheesemaking 6

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Part II: From milk to cheese[edit | edit source]

Chapter 1: Milk[edit | edit source]

Definition and composition

Fresh milk is a white liquid, with an agreeable odour and a faintly sweet taste, produced by female mammals to feed their offspring. Humans use cows' milk as well as buffaloes', goats', sheep and mares' milk, either to drink directly or to make into different foods, such as cheese, butter, cream and yoghurt.

Seven-eighths of milk is water, with solids the nutritious part forming the remaining one-eighth. The solids can be broken down approximately as follows (see also Table):

One hundred kg of milk contains approximately 87 kg or litres of pure water and 13 kg of solids.

Milk production

Several factors affect the quality of milk, and to obtain the high-quality clean milk necessary for cheesemaking particular attention must be paid to the animals' diet and health and to the standard of hygiene in the milking parlour.

Diet

The following are all suitable as animal feed but may affect the colour, taste or smell of the milk in different ways:

• Natural or artificial pasture (gives a yellow butterfat due to the
  presence of Beta Carotene Vitamin A)
• Hay (gives a white butterfat and a rather colourless butter)
• Silage (which is not suitable for hard cheese)
• Fresh meal, especially if mixed with molasses.

Milk: a balanced food.

Health

Milk must not be used for cheesemaking if the animal is diseased or sick in any way and care must be taken to prevent the following:

• Aftosis (foot-and-mouth disease)
• Brucellosis or undulant fever: (brucella abortus in bovines and brucella melitensis in goats)
• Mastitis
• Tuberculosis.

Milk must also be excluded from cheesemaking if it shows any chemical or physical abnormality, for example:

• If the milk contains colostrum (until the sixth day after the birth)
• If the milk contains antibiotics (until five full days after the last injection)
• If the animal has been vaccinated within the previous 24 hours
• If the milk has an abnormal flavour or aroma
• If the milk has an abnormal colour, for example bloody.
• If the milk is contaminated (with, for instance, dung, cattle feed or sediment).

The milking procedure

Before milking

• Clean and disinfect the milking parlour (this should have a hard floor that can be cleaned after each milking).
• Brush off the animal's flanks if they are dirty.
• Wash all utensils with a good dairy disinfectant and rinse with clean water.
• Wash the udder with lukewarm water and disinfectant with a cloth used for this and no other purpose.
• Wash and disinfect the milker's hands.
• Control mastitis. This disease will destroy the udder and produces an abnormal milk.
• Ensure that all milkers and cheesemakers are clean and healthy.

After milking

• Wash all utensils immediately after use and keep them in a clean place.
• Cool the milk to at least 15 C.

It is also important to remember the following:

• In hand milking do not give the last milk to calves because it contains the highest proportion of fat.

Instead, milk three teats completely and leave the fourth for the calf.

• Never mix new milk with old.
• Don't use cloth filters because they are very difficult to clean and may contaminate the milk.
• Don't use milk buckets for other purposes.
• Don't use rusty or oxidized churns or equipment.
• Don't leave milk churns or receptacles full of water.
• Send milk destined for cheesemaking to the cheese factory or dairy immediately after milking to prevent bacterial spoilage.
• Wash, scrub well and rinse all equipment daily with hot water, detergents and a dairy disinfectant.

Mastitis detection (Califomia mastitis test)

This test determines the presence or absence of leucocytes (pus indicating infection) in milk. There is a close relation between the number of leucocytes present in the sample and the degree of reaction.

Equipment

A pallet with four small numbered receiving dishes (Figure 5).

A narrow-necked plastic measuring bottle containing reagent. (A suitable reagent is one resazurin tablet and one rennet tablet dissolved in 50 ml distilled water.)

Method

1. Extract a few squirts of milk from each teat into the corresponding dish in the pallet (Figure 5).
   2. Tilt the pallet to one side to equalize the amount of milk in each dish, leaving about 2 ml in each.
   3. Add the same amount of reagent to each dish according to instructions.
   4. Gently agitate the pallet to mix the milk and reagent. Wait for 30 to 60 seconds and observe the results.

File:SK17016A.GIF

Figure 5. Testing for mastitis

Results

Normal milk: The milk does not congeal and its colour does not change.

Slightly infected milk: Small clots will form, the milk will thicken very slightly and the colour will darken. (The colour produced will vary according to the type of reagent used.)

Heavily infected milk: The milk will become very thick and dark.

Recommendations

Slightly infected milk should be separated from healthy milk and pasteurized before use. Antibiotics are not necessarily recommended for light cases of mastitis; improved dairy hygiene and frequent strip milking should be sufficient to cure these cases.

Heavily infected milk should never be used for cheesemaking and must be kept completely separate from good milk. It should be boiled and used as calf feed. In serious cases of mastitis it is advisable to consult a vet.

Precautions should be taken in all cases of mastitis not to spread the infection from affected animals to healthy ones through hands, towels and milking machines. Apart from special attention to hygiene, affected cows should be milked last. If a milking machine is used, a re-usable, cheap, in-line filter can be used to detect mastitis, which shows up on a fine screen as small lumps or particles.

Reception

Milk should arrive at the cheese factory as soon as possible after milking to prevent excessive acid development; too high a level of acidity will damage the cheese. The milk should be received and weighed outside the plant to avoid suppliers having to enter the building and so prevent possible contamination. As all equipment for transporting and holding milk must be washed with hot water and a good dairy detergent and rinsed immediately, facilities for this should be provided in the reception area.

Analysis

A series of tests determine the milk quality and ensure that the milk is pure, clean and suitable for cheesemaking. The main tests are:

Sensory analysis

• Odour free from acidity and containing no foreign substances.
• Taste normal or strange?
• Appearance colour and consistency.

Laboratory tests

• Bacteriological
• Physio-chemical
• Titration of acidity
• Percentage of fat
• Density of milk
• Control of impurities

Reductase Test

This test, based on the speed with which milk changes colour as a result of the reaction between methylene blue (methylthionine chloride) and bacteria, indicates the level of bacteria in the milk.
Equipment and reagents

Reductase tube approximately 25 ml capacity, ringed at 10 ml
A jug for the sample
A 37 C incubator, with test tube
A 1 ml pipette Methylene blue All equipment must be sterilized.

Method

1. Cool 200 ml of distilled water to 40 C.
2. Add one tablet of methylene blue and let it dissolve completely. (Keep this solution in a dark bottle and do not expose it to light.) Note: Since methods differ from country to country, it is advisable to follow the instructions of the producer of methylene blue solution.
3. Pour 10 ml of milk into each test tube.
4. Add 1 ml of methylene blue solution to each test tube.
5. Agitate the tubes to mix the solution with the milk.
6. Place the test tubes in the incubator at 37 to 38 C and check them every hour.

Results

If two-thirds or more of the milk in a test tube becomes discoloured in less than the acceptable time given below, it should be rejected.

Recommendations

Milk which discolours before two hours should not be used and indicates a lack of hygiene in its production: badly washed churns and milking equipment, improper cooling temperatures or impure water favouring the growth of undesirable micro-organisms.

Acidity determination

The level of acidity in milk relates to its microbiological content and therefore can indicate its purity and freshness. It can also be used to calculate the effectiveness of the lactic cultures being used in the cheese plant and the time required to reach desired levels of acidification.

Equipment and reagents

A clear flask
An eye-dropper
An acidimeter
A 10 ml milk pipette
A one-tenth solution of sodium hydroxide (NaOH)
An indicator solution of phenolphthalein in 2 per cent alcohol

Method

1. Add 9 ml of the milk to the flask.
   2. Add three or four drops of phenolphthalein.
   3. Fill the burette of the acidimeter with the solution of NaOH and begin to titrate the milk in the flask. The titration is complete when the milk turns pink and remains so for at least 10 seconds.

Result

The acidity in Dornic is equal to the number of 0.10 ml of NaOH used.

Recommendations

Fresh milk should normally have a reading of between 16 and 18 Dornic. In remote mountainous areas, however, readings of up to 20 Dornic, resulting from long trips over mountain passes often on mule or horseback, are acceptable. If the milk has an acid level of more than 20 to 21 Dornic, 6 to 10 per cent of clean water may be added, as soon as the milk arrives at the cheese factory, in order to reduce the acidity.

File:SK17019A.GIF

Figure 6. An acidimeter

File:SK17019B.GIF

Figure 7. A pH meter