Technical Notes 

Note: These technical notes are not indexed to illustrations numbers.  They are taken from:
 

CHEESE MAKING TRAINING COURSE
RIT Lampang
24th - 28th October 1989

CHEESE

General introduction

The changing of milk into cheese generally goes through four stages:

1. Coagulation: physical and chemical changes in the casein micelles (protein) due to the action of proteolytic enzymes and/or lactic acid leading to the formation of a protein network.

2. Drainage: separation of the whey after mechanical cutting and agitation of the coagulum followed by moulding and, depending on the kind of cheese, pressing.  By this means, cheese is obtained.

3. Salting: incorporation of salt by dry salting on the surface or within the body of the cheese, or by immersion in brine (salt water).

4. Ripening: biochemical changes in the cheese brought about by mainly bacterial enzymes.

Coagulation

Milk contains two different groups of proteins.  These are:

-  the casein complex (75-80 % of total protein);
-  the whey proteins (20-25 % of total protein).

It is the casein that coagulates when making cheese.

The components in milk are present in different physical states such as true solution, colloidal dispersion or emulsion.
 

There are different: 
- textures 
- ways of ripening 
- compositions. 

By taking good quality milk and: 
- cooking 
- renneting 
- straining. 

By taking fresh cheese and: 
- pressing 
- ripening. 

There are defects of: 
- flavour 
- texture 
- appearance. 

A component which is present as an emulsion will precipitate or rise to the surface by the force of gravity if left to stand (milk fat). 

The casein is present in the milk as small micelles.  The outsides of these micelles have a large excess of negative charge.  The effect of this is that the micelles repel each other.  Thereby avoiding aggregation ---> sedimentation. 

 Figure 1: Structure of the casein micelle 

The casein micelles also bind a lot of water (hydration).  This bound water protects the micelles against aggregation. 

In order to coagulate the milk (casein) it is necessary to destabilize the casein dispersion.  This can be done by acid or enzyme. 

Acid coagulation:  By adding acid (H+) to the milk, pH is lowered and the ionization is reduced.  When so much acid has been added that there is a neutral charge on the micelles (- and + equals), (isoelectric pH = 4.2) and the hydration is significantly reduced, a coagulum will form.  This reaction depends very much on temperature.  At higher temperatures the coagulum will form at a higher pH (less acid). 

Rennet produces a firm and elasticcurd

Figure 2: Changes in micelle structure in the course of acidification 

Primary phase: Also called the enzymatic phase.  The enzyme attacks the stabilizing components of the micelles.  A piece of the casein which has a strong negative charge is cut off and hydrophobic (water rejecting) bonds between the casein micelles can be established.  The enzymatic phase is in particular influenced by temperature, pH and amount of enzyme.  The optimum temperature for rennet enzyme is 40 - 42 C but usually a temperature of around 30-32 C is used because of other factors which will be explained later.  The effect of pH can be seen from Figure 3 below. 

Figure 3: Effect of pH on the firming rate and the maximum firmness of rennet coagulum

The total time for the primary and secondary phase is from 30 to 45 minutes depending on the factors mentioned. 

9 You need good quality milk with few bacteria.

Cheese made from milk with high bacteria content has a bad flavour.

Do not use milk from cows with mastitis or other diseases.
 

It turns into curd on heating  and the curd is too soft.
 

By CUTTING the coagulum into smaller pieces the total surface becomes much bigger and the expulsion of whey (syneresis) increases.  In order to control the drainage it is very important to cut the coagulum in equal-sized cubes. 

This can only be done by using a proper sharp instrument and by cutting when the coagulum has reached a proper firmness.  If cutting is done roughly or with poor instruments too many fine curd particles will be the result.  These particles (fines) are lost in the whey resulting in lower cheese yields. 

After cutting, the curd is usually left undisturbed for a while so that more whey comes out thus resulting in firmer cubes which can stand STIRRING.  The stirring is at first done very gently to avoid damage to the cubes.  As the cubes become firmer the stirring can be intensified.  The stirring has two major purposes.  It prevents the cubes from settling and sticking together and it makes the cubes bump into ONE ANOTHER whereby whey is pressed out. 

While stirring the curd is usually cooked (scalded) as well.  The COOKING increases the whey expulsion.  Cooking means heating to a certain temperature, depending on the type of cheese produced.  Two different methods for cooking are possible. 

- direct addition of hot water or steam 
- hot water or steam in the double jacket of the cheese vat. 

When adding hot water direct into the curds, 1/3 of the whey is often removed first.  Apart from raising the temperature, the addition of water will lower the concentration of the dissolved components of the whey and the curd.  A lower lactose content in the curd will result in lower acid production and consequently higher water content in the final cheese. 

Cooking should be done carefully, the temperature should not rise too quickly and it is important that the whey-cheese grain mixture is stirred continuously. 

After cooking stirring is continued for some time to expel more whey. 

When the curd reaches the required firmness (when it is dry enough) it is processed according to the type of cheese to be made. 

This may involve: 

- Forming into cheese-loaves and pressing before salting in brine and ripening i.e. Gouda, Tilsitter 

Pasteurization does not destroy all bacteria from dirty utensils.

Cleaning agents and disinfectants in cheese milk kill lactic acid bacteria which are necessary for cheese.

This contains some bacteria which pasteurization does not destroy.

STARTER CULTURE

The mother culture to be used for cheese-making is usually a mesophyllic culture.  This means that the bacteria have an optimum growth temperature of about 25-30 C and that they will grow between 10 and 45 C. 

For Mozzarella, however, the same bacteria as for yoghurt are used.  These are thermophilic cultures with an average optimum growth temperature of about 50 C and they will grow between 10 and 80 C.  The two most common strains used are Lactobacillus bulgaricus and Streptococcus thermophilus, both with optimum growth temperatures between 40 and 45 C.  These bacteria are used for Mozzarella because of their fast growth and high acid production. 

The yoghurt culture is usually supplied from the manufacturer as a freeze-dried culture (Lyophilized Culture) or concentrated deep-frozen culture. 

The preparation of yoghurt culture is shown below. 

Figure 4 

- tasting
- smelling

bad tastes and smells go to your cheese

- boiling

sour milk or milk with colostrum precipitates.
 

GERBER TEST FOR FAT CONTENT

Reagents:
   Sulphuric Acid: sp. gravity 1.816 +/- 0.003, 20 C. 
   Isoamyl alcohol: sp. gravity 0.811 +/- 0.002, 20 C. 

Equipment 
  Butyrometers
   Stoppers 
   Pipette 10.73 ml 
   Pipette for H2SO4 10 ml 
   Pipette for Amyl alcohol l ml 
   Gerber Centrifuge 
   Water-bath 67 C 
   Cloth to hold hot butyrometers 

Procedure:

1. Fill 10 ml sulphuric acid into butyrometer. 

2. Thoroughly mix the milk sample and, using the milk pipette add 10.73 ml milk. 

3. Add 1 ml isoamyl alcohol on top of the milk.  Care must be taken not to get milk, sulphuric acid or alcohol on the neck of the butyrometer, if this is allowed to happen the stopper may slip out. 

4. Push the stopper in the butyrometer. 

5. Shake the butyrometer thoroughly until the milk is dissolved.  Hold the stoppered end up.  Take care!! The butyrometer becomes HOT. 

6. Holding the bottle by the stopper and neck.  Invert it about 10 times to mix the acid remaining in the bulb with the content. 

7. Adjust the stopper so that the expected fat % can be read. 

8. Centrifuge for 5 minutes. 

9. Immerse the butyrometer in a water-bath at 67 C for 5 to 10 minutes. 

21 You add rennet to milk to coagulate it.
 

10. Adjust the fat column onto the calibrated section of the tube and read as shown in the figure below.

 Figure 5 

STANDARDIZATION

To guarantee the consumer a product of constant fat content and to meet standards, the fat content for milk products should be standardized.  Usually the fat content of raw milk is higher than the required standards.  Manufacturing products with an excess fat content will lead to financial losses.  In small scale operations the cost of standardization (i.e. purchase and maintenance of separator, fat testing equipment etc.) may be higher than the profits especially if the cream cannot be sold. 

Standardization can be undertaken by: 

1. Mixing whole milk with partly or totally skimmed milk. 

2. Mixing skimmed milk with cream. 

3. Separating whole milk to get the required fat content. 

Method 3 requires very sophisticated and expensive equipment so under small scale only methods 1 and 2 are of interest. 

Example 1

Suppose 200 kg of raw milk is available.  The fat test has shown a fat content of 4.5 % fat.  Milk with 3 % fat is required for cheese production.  How much raw milk is it necessary to skim (separate).  In the calculation it will be assumed that all the fat is removed from the skim milk by separation. 

If X     = litres of cream with 32 % fat 
and Y  = litres of milk with 3 % fat 

- makes the cheese soft, rubbery, hard or brittle

The following equation may be used. 

In the calculation the expression fat unit (fu) means 1 % fat in 1 litre of milk. 

Total fat units = 200 1 x 4.5 % fat   = 900 fu 

I X + Y =  200 
II 32X + 3Y = 900 

Equation I should be multiplied by 32 so that X will be eliminated by subtraction. 

I2  32X + 32Y = 6,400 
II2  32X + 3Y =   900 

Equation II should then be subtracted from Equation I and the following is obtained. 

III  29Y = 5,500 
III2    Y =   189.7 l with 3 % fat 

The Value Y should be inserted in I: 

IV X + 189.7 = 200 
IV2 X  =  10.3 l cream 32 % fat 

Now it only remains to calculate how many litres to skim to get 10.3 l of cream with 32 % fat. 

10.3 l x 32 % = 329.6 fu 

329.6 fu  = 73 litres to be skimmed 
4.5 fu/l 

Control of calculation: 

189.7 l x 3 % fat  = 569.1 fu 
10.3 l x 32 % fat  = 329.6 fu 
     898.7 ~ 900 fu

See T 10.1 Starter Cultures.

If skim milk is available for mixing with whole milk to obtain standardized milk with a certain fat content the following mixing square may be used. 
 

The square shows: 

H = fat content of the milk with the highest fat content (e.g. whole milk with 5 % fat) 

L = fat content of the milk with the lowest fat content (e.g. skimmed milk with 0.05 % fat) 

S = fat content of the standardized milk to be produced (e.g. 3 % fat) 

QH = quantity of milk available with highest fat content, that is milk to be standardized 

QL = quantity of milk with lowest fat content; to be mixed with milk with highest fat content 

In the example, H - S = QL = 5 - 3 = 2, and S - L = QH = 3 - 0.05 = 2.95, which means that for every 2.95 kg of whole milk 2 kg of skimmed milk has to be added to obtain standardized milk with 3 % of fat; in this case that is 4.95 kg of standardized milk.

Add 5-20 g calcium chloride per 100 l milk.

34 You can add potassium nitrate to prevent too much gas in your milk (from coliform or butyric acid bacteria).

Add 10-15 g potassium nitrate per 100 l milk.

35 10 l of milk makes
1 kg of semi-hard cheese or
2 kg of soft cheese (it contains more whey).

Assumptions: 

Approx. 90 % of the fat goes into the cheese. 
Approx. 75 % of the protein goes into the cheese. 
Approx. 0.5 kg of sugar + ash per 100 kg of milk goes into the cheese. 

Calculate the yield from 100 kg of cheese milk with the following composition. 

Fat content                                                = 4.2 % 
Protein content                                          = 3.4 % 

Assumed water percent in cheese               = 40 % 

Fat yields:  100 x 4.2 x 90 %                     = 3.78 kg ~ 33% 
                       100

Protein yields: 100 x 3.4 x 75 %                = 2.55 kg ~ 22 % 
                            100 

Sugar + ash yields:                                    = 0.50 kg ~ 4 % 

Total dry matter                                        = 6.83 kg 

Water yields:  6.83 x 40                            = 4.55 kg ~ 40 % 
                         60 

                                                               =11.38 kg ~ 60 % 

Kg of milk per kg of cheese  100             = 8.8 kg/kg 
                                           11.38 

Fat in dry matter  3.78 x 100                    = 55 % = 55+ 
                                6.83 

Semi-hard cheese - you can slice.

Soft cheese - you can slice or spread.

37 Fresh cheese

Cheese ripened by bacteria/enzymes

Cheese ripened by mould.

38 Different cheeses contain different amounts of fat and water.

ACIDITY TEST 

The titratable acidity test is employed to ascertain if milk contains a large amount of lactic acid which might reduce its heat stability, and thereby its suitability for milk products manufacture. 

Titratable acidity generally has been presented as the acidity measured by titration with 0.1 N sodium hydroxide, due solely to lactic acid.  This is not really so because what is actually measured is the quantity of alkali necessary to bring the pH of the milk to approximately 8.3 at which point phenolphthalein shows the characteristic pink colour.  Generally, freshly-drawn milk does not contain lactic acid.  Some bacteria which contaminate milk can attack the milk sugar (lactose) and form acids of which the principal is lactic acid.  The indicator substance phenolphthalein is colourless in an acid solution but red in an alkaline solution.  On adding phenolphthalein to milk it remains colourless because the milk is acidic, its inherent acidity being due to its natural constituents particularly the protein and phosphates.  The addition of a solution of an alkali like sodium hydroxide neutralizes the acid and, when a slight excess has been added, the phenolphthalein turns red. 

Method

1. Pipette 9 ml of the well-mixed sample of milk into a 100 ml Erlenmeyer flask. 

2. Add 10 drops of 1 percent phenolphthalein solution (prepared by dissolving 1 gm phenolphthalein in 75 ml of 95 % Ethyl alcohol and adding enough distilled water to make total volume 100 ml). 

3. Fill the burette with the 0.1 N sodium hydroxide solution, run out a portion to ensure that there are no air bubbles in the column, then adjust to a convenient graduation mark, preferably zero. 

4. While agitating the sample continuously, run the sodium hydroxide solution in slowly from the burette until the first permanent pink colour is obtained.  A permanent very pale pink is the correct endpoint. 

5. Read off the quantity of alkali used and calculate the amount of titratable acidity as percent lactic acid. 

Titratable acidity = ml 0.1 M NaOH x 0.009  x   100 =  % lactic acid 
                                            Volume of sample 

Example: Volume of sample 20 ml 

 ml 0.1 M NaOH = 29 ml 

Titratable acidity = 29 ml x 0.009 x 100 = 1.3 % lactic acid 
                                              20 ml 

- taste

too much whey makes the curd sour

- keeping quality

too little whey makes it easy for bacteria to attack the curd.
We usually remove more whey from fresh cheese than from cheese for ripening.

SMALL SCALE MOZZARELLA
CHEESE MANUFACTURING 

Cheese vat, jacketed 100-200 l 
Curd cutting knife 
Agitator 
Scale 
Thermometer 
Heat source (gas-burner) 
Basin for heating water in 
Basin for heating cheese in water 
Knife 
Sieve 
Cheese cloth 
Bucket 
Gloves 
Moulds 
Wrapping material 
Freezer/Refrigerator 

Optional equipment: pH-meter

Lactodensimeter 
Fat testing equipment 
Acidity testing equipment 
Electric incubator 
Vacuum packing machine 
Separator

Materials: 

Milk (standardized fat %) 
Yoghurt starter culture 
Rennet (powder or liquid) 
Salt (NaCl) 
Ice 

Procedures:

1. Raw milk is poured into the cheese vat through a cloth.  The temperature should be > 32 C

2. 1.25 % yoghurt starter is added and the milk is thoroughly stirred.  Leave to stand for 30 minutes. 

3. Add rennet according to instructions from supplier.  Stir milk to ensure equal distribution of rennet.  Leave untouched until a shiny firm coagulum has formed (35-45 minutes).

- quantities of rennet or culture
- times for curdling
- temperatures for curdling.
 
 

Each time you make cheese, keep records:

4. Cut the curd into equal sized cubes of 1 to 1.5 cm.  Cut horizontally first, then twice vertically, if cubes are too big cut again vertically.

5. Start heating with low fire and leave to stand for 15 minutes. 

6. Start stirring gently and put on full fire.  Gradually intensify stirring.  Keep on stirring and heating until the temperature is 47 C.  Stop heating and keep on stirring for about 30 minutes. 

7. Stop stirring.  The cheese grains will then sediment on the bottom of the vat.  Remove with a clean bucket as much whey as possible.  Pour the whey through a sieve into a milk churn or another container.  Push cheese grains away from the outlet, insert a sieve in front of the hole and remove remaining whey through outlet. 

8. The cheese grains will stick together within 5 minutes after removal of the whey.  Cut the lot into pieces of approx. 25 x 25 cm and turn them.  Put lid on the vat. 

9. Cut, turn and pile the cheese every 30 minutes for 1 1/2 hours of until pH has reached 5.1 - 5.3.  The cheese should be like boiled chicken meat. 

10. Cut the cheese into ribbons of approx. 25 x 8 cm.  Weigh out 2.2 kg, put them into a basin with holes in the bottom of the side. 

11. Insert basin into another basin containing water at 82 - 85 C.  Leave the cheese there for 10 minutes. 

12. Take basin with cheese out, knead and stretch the cheese vigorously while it is hot.  Add salt (one spoonful per 2 kg) and knead again. 

13. Insert cheese in hot water for short time (1-2 minutes) take it out, shape it and fill it in the mould. 

14. Put mould with cheese into ice-water. 

15. Cool the cheese in the ice-water until it becomes firm, about 1 hour. 

16. Let the surface of the cheese dry before packing. 

17. Put the packed cheese in the freezer or refrigerator.

1. Gary H. Richardson, Ph.D.; Standard Methods for the Examination of Dairy Products, 15th edition. 

2. Jeremija Lj. Rasic, Joseph A. Jurmann; Yoghurt, Fermented Fresh Milk Products, Volume 1. 

3. Egil Waagner Nielsen; Maelkekemi, 1985. 

4. J.C.T. van den Berg; Dairy Technology in the Tropics and Subtropics, 1988. 

5. C.D. Thomson, A. Eck; Cheese Making, Science and Technology. 

6. J.C. Lambert; Village Milk Processing, FAO Animal Production and Health Paper No. 69. 

7. G.H. Wilster, Ph.D.; Practical Cheesemaking, Thirteenth Edition, 1980. 

8. Frank Kosikowski; Cheese and Fermented Milk Foods, Second Edition, 1978.

Cheeses which are ripening should be kept in a cool place at 10-15 C until they are ripe, not in a refrigerator.

It has a high water content (70-80 %) and a fat content of 5-20 %

Try not to use plastic as it is difficult to clean and absorbs smells.

Do not use iron or zinc as these can corrode quickly.

A source of cooling e.g.ice, water.

A spoon for measuring the culture.

Knives with long handles or split cane bamboo for cutting the curd.

A thermometer for measuring outside temperature for making culture and ripening cheese.

It should measure about 45 x 60 cm and you should use it folded double.

A bucket for collecting the whey.

Clothes pegs for holding the cloth over the bucket.

Wooden draining board on which to place the cheese mould while it drains.

Then cool to 20 C

- add ¹/₂ l mesophyllic starter culture

- add rennet according to the instructions on the bottle or packet.

In this time the milk sours and curdles.

Too much rennet (or too high a temperature) makes the curd soft.

Fit into a bucket.

Fix with clothes pegs.

The curds remain on the cloth and the whey filters through.

77 If you cannot get starter culture, you can use acid from fruit or vinegar.

Stir all the time.
Cool to 20-30 C.
 

The outside temperature should be cool.
 

81 Yes, you can add flavours such as salt, curry, chili, garlic or other herbs and spices.

- cooking the whey in a pot with a cup

- adding sugar, cloves or cumin for flavour

- gentle cooking for about 5 hours until the whey is nearly solid

It has a water content of 40-50 % and a fat content of 20-35 %.

89 You need equipment for:
- moulding
- pressing
- salting
- ripening.

- a flowerpot with holes in the bottom

(do not use it for long or it will begin to rust)
 

(do not use plastic tubes from building work as these contain poison).

Important: If possible, make holes from the inside to the outside.

Cheese mould with a lid made from a wooden barrel.
 

It has a lid which is used to press the cheese.
length : 20 cm
width : 20 cm
height : 12 cm
 

It has no ends and holes in the sides.

- 2 metal plates
5 cm long by
2¹/₂ cm wide

- 2 nuts and bolts
8 cm long by
³/₄ cm in diameter.

The plates can be bigger or smaller as required.

Adjust the pressure often as the cheese shrinks.
 

Place the cheese inside a container with no ends and with holes in the sides on a clean flat base.

Put a lid on top.

if the weight of the stone is 10 kg

the press is 10 x 2 = 20 kg.

the temperature should be 12-16 C and it should not be too dry

- raw milk
- mesophyllic starter culture
- rennet powder or liquid
- salt (NaCl)
- calcium chloride (CaCl₂) and potassium nitrate (KNO₃), optional.
 

Put the knife under the cut and lift up gently.
 

Cut the curd into cubes with a side length of 10-15 mm.

While stirring pour small amounts of hot water at 65-70  C into the cheese until the mixture reaches a temperature of 36-38 C.
 

Use a sieve and cheese cloth to catch cheese grains and return to the cheese.
 

Place a cheese cloth inside a cheese mould.

Warm in hot water just before use.

Do not let the curd cool.

Use only clean hands for filling.
 

Press with twice the weight of the cheese (for every 1 kg cheese use 2 kg press).
 

wrap the cheese in a new, clean cheese cloth and turn upside-down

put the cheese back in the mould.

Press for 2-3 hours for lighter cheeses and 4-5 hours for heavier cheeses.
 

Use ice if necessary.

Put the cheese in the brine at a temperature of about 15 C.

Make the time longer or shorter by taste.

Ripen it on clean wooden shelves for at least 4 weeks at a temperature of 12-16 C.
 

This prevents fungi.

Put the cheese back upside down.

Bitterness can come from protein breakdown.

Tough curd comes from too high a temperature at cooking.
 

- your starter culture is too old

- your milk contains chemicals that stop bacteria multiplying e.g. antibiotics from mastitis treatment.
Always wait 5 days after antibiotic treatment before using milk.

Slimy growths may be white to yellow/brown and come from moulds or bacteria.
 

 

What cheese is

Curds separated from whey

(5-8)

Items for making cheese

1 Good quality milk	(9-20)
2 Rennet	(21-26)
3 Starter	(27-32)
4 Additives	(33-34)

Quantity of cheese from milk

(35)

Important things in cheese making

1 Factors affecting type of cheese	(36-40)
2 Adapting recipes and keeping records	(41-42)
3 Problems of cheese making	(43-46)
4 Keeping qualities of cheese	(47-50)

Two common types of cheese

1 Fresh cheese	(51-52)
- equipment	(53-62)
- manufacture	(63-76)
- working without starter	(77-80)
- flavouring	(81-82)
- using whey	(83-86)
2 Semi-hard ripened cheese	(87-88)
- equipment	(89-107)
- manufacture	(108-131)

Defects of cheese

1 Flavour	(132-133)
2 Texture	(134-135)
3 Appearance	(136)