2002

 

 

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 Cheese and Cheese Making

 References. The Dairy Processing Handbook by Tetrapak Processing Systems AB, Sweden, contains valuable information about this subject. The book Cheese and Fermented Products by Frank Kosikowski has descriptions of procedures for many varieties.

 

 Background.

  Terminology for Classification of Cheese. Codex Alimentarius, FAO/WHO, has issued Standard A6 as a definition for cheese products.

Cheese is the fresh or ripened solid or semi-solid product in which the whey protein/casein ratio does not exceed that of milk obtained:

 Classification of Cheese. The moisture content of cheese serves as the first term to distinguish various categories. The fat content is the second term, and curing characteristics represent a third term.

 Moisture Content. The moisture content of cheese is reported on a fat-free basis (MFFB), as shown:

 Fat Content. The fat content of cheese is reported on a dry solids basis (FDB), calculated as shown:

 Curing Characteristics.

  1. Cured or ripened cheese is cheese which is not ready for consumption shortly after manufacture but which must be held for such time, at such temperature, and under such conditions as will result in the necessary biochemical and physical changes characterizing the cheese.
  2. Mould cured or mould ripened cheese is a cured cheese in which the curing has been accomplished primarily by the development of characteristic mould growth throughout the interior and/or on the surface of the cheese.
  3. Uncured, unripened, or fresh cheese is cheese which is ready for consumption shortly after manufacture.

 Designation of Terms for Classification of Cheese. The following three terms apply to all cheeses covered by the A6 Standard under Codex Alimentarius. However, this classification does not preclude the designation of more specific requirements in individual cheese standards.

1st Term

designation

Moisture %

fat-free basis

  2nd Term

designation

Fat %

total solids basis

Extra hard

< 41

  Skim

<10

Hard

49-56

  Low fat

10-25

Semi-hard

54-63

  Medium fat

25-45

Semi-soft

61-69

  Full fat

45-60

Soft

>67

  High fat

>60

3rd Term

designation

Principal curing characteristics

1. Cured or ripened a. Mainly surface

b. Mainly interior

2. Mould cured or ripened a. Mainly surface

b. Mainly interior

3. Uncured or unripened No curing; must be made from pasteurised milk

 

General Procedure from Milk to Hard and Semi-Hard Cheese.

Pretreatment of Milk for Cheese:

 Optional Additives

 Necessary Additives

Coagulum Determine the readiness of the coagulum by making a very thin vertical slit, about 3-5 cm long, in the surface of the gelled milk. Insert the knife blade at a shallow angle under the length of the slit. Gently tilt the knife tip upward to break the coagulum. A ready-to-cut curd will break along the slit, forming a deep wound with uniformly curved side walls and with only a little whey at the bottom. If the wound tends to collapse, it is not yet ready. If there is much whey, it should have been cut earlier.

  • Cutting into grains. For village operation, the curd may be cut with a long knife using long parallel strokes (about 1 cm apart) in one direction and then, in a similar fashion, across in the other direction. This will produce vertical columns of cut curd. These columns are now divided by making shallow horizontal strokes with knife in several directions to reach the walls of the tub (see diagram).

  • Cutting curd into grains with wire cutters. These are stainless steel frames strung with thin wires or thin blades. For manual cutting, the vertical cutter (A) is inserted along the end wall of the cheese vat and then pulled in long firm strokes to the other end. Several paths may have to be cut before all curd is cut in one direction. The same instrument is then used to make perpendicular cuts across the vat. Finally, the horizontal cutter (B) is used to cut in one direction only, to divide the curd into cubes.

  • Mechanical cheese vat. A set of vertical and horizontal "cutters" are attached to overhead rotating arms which move back and forwards in the vat. Mechanical cheese vats may have a capacity to hold as much as 10,000 liters of milk. The construction needs to be oval in shape for the cutters to reach all points near the walls of the vat.

 

Whey Expulsion (Syneresis). The aim of cheese making is to obtain a curd with a defined moisture content. This is achieved by a controlled expulsion of whey from the curd particles. The cutting of the curd is done to facilitate whey expulsion by creating a much greater surface for drainage. Stirring of the curd also promotes whey drainage by the mechanical action and by preventing the particles from adhering to one another.

Pre-stirring. Immediately after cutting, the curd grains are very sensitive to mechanical treatment and the initial stirring must be gentle to avoid breaking the curd into "fines". However, agitation must be sufficient to prevent the grains from "matting" together into lumps. Curd made from skim milk has a strong tendency to settle at the bottom of the vat and the stirring must be more intense than with full-fat cheese.

Pre-drainage of whey. For some varieties of cheese, it is practice to remove some of the whey from very full cheese vats so that hot water can be added for temperature adjustment. For each cheese variety, is important that the amount of whey - normally about 35%, sometimes as much as 50% of the batch volume- is kept consistent in the daily routine.

Heating/cooking/scalding. Heat treatment is required during cheese making to regulate the size and acid development of the curd. Heat causes contraction of the curd particles with increased expulsion of whey. More importantly, heat is used to regulate the growth of the lactic acid bacteria and control acid development in the curd. The time and temperature programme for heating is determined by the type of cheese and the method of heating (direct heating by adding hot water; indirect heating in a jacketed vat). Heating to temperatures above 40C , sometimes called cooking , normally takes place in two stages

At 37-38C the activity of the mesophilic lactic acid bacteria is retarded, and heating is interrupted to check the acidity by titration of the whey. Then, heating is continued to the desired final temperature. Above 44C the mesophilic bacteria are totally deactivated, and they are killed if held at 52C for periods of 10-20 min.

Heating beyond 44C is typically called scalding. Some types of cheese, such as Emmenthal, Gruyere, Parmesan and Grana, are scalded at temperatures as high as 50-56C. Only the most heat-resistant lactic-acid producing bacteria are can survive this treatment. Included is Propionibacterium Freudenreichii ssp. Shermanii, which is the prominent fermentation organism for the structure and aroma characteristics of these cheese varieties.

Final stirring. The sensitivity of the curd grains to mechanical action decreases as heating and stirring continues. More whey is excluded from the grains during the final stirring period, primarily due to continuous development of lactic acid, but also by the mechanical effect of stirring. The duration of final stirring depends upon the cheese variety and is dictated by the desired moisture content.

Final removal of whey. As soon as the required acidity of whey and firmness of the curd have been attained the residual whey is drained off in various ways.

Final treatment of curd. The curd can be treated in several ways after all the free whey has been drained away. It can be:

Transferred directly to moulds (granular textured cheeses) and pressed.

Pre-pressed into a slab and cut into pieces of suitable size for placing into moulds (round-eyed cheeses) for final pressing.

Exposed to a cheddaring process, the last phase of which includes milling into chips which can be dry-salted and either hooped or, if intended for Pasta Filata types of cheese, transferred unsalted to a cooking-stretching machine.

Pressing For pressing into the desired shape and removal of residual whey, the curd blocks are wrapped in cheese cloth and placed in a suitable cheese mould and pressed for some hours. The amount of pressure and the length of time varies with the type of cheese.

 

Salting. Salting takes place after the cheese has been pressed, often starting the following day. In cheese as in many other foods, salt normally functions as a condiment. However, salt has other important effects, such as retarding starter activity and microbial processes associated with cheese ripening. Application of salt to the cheese block causes more moisture to be expelled, both through osmotic effects and a salting effect on the proteins. With few exceptions, the salt content of cheese is 0.5-2%. Blue cheese and Feta cheese, however, have a salt content of 3-7%. The exchange of calcium for sodium in paracaseinate has a favourable influence on the consistency of the cheese, which becomes smoother.

 

Preparation of Common Brine Solutions. Brine is made by dissolving salt (sodium chloride) in water or sometimes whey. The difference in osmotic pressure between brine and cheese causes some moisture to be expelled with its dissolved components, including whey proteins, lactic acid and minerals , in exchange for NaCl. The use of whey minimizes the concentration differences for the dissolved milk constituents but makes it more difficult to control the salt concentration by density measurements. Brine is kept in continuous use over weeks and months but the salt concentration must be replenished each day. Aside from the loss of salt by penetration into the cheese, an equilibrium state will eventually be attained by the dissolved whey constituents and by pH. For this reason, "old" whey is considered best for development of the proper cheese quality, both flavour and texture.

Salt Concentration. The desired salt concentration is maintained by daily measurements of the density of the brine using a hydrometer (Be) or by using a refractometer calibrated for the brine composition. The following table shows the composition of salt/water solutions. Note the differences between expressing salt concentrations as weight-by-weight and weight-by-volume. The difference occurs because the volume of the solutions is increased by salt addition, but only by 0.33-0.36 liters per kilogram of salt.

Density versus Salt Concentration

Salt added to 100 L water

Volume of

solution

Salt

concentration

Density (15C)

(kg)

(L)

(% wt/wt)

(% wt/vol)

(kg/L)

(Be)

15.7

19.3

23.1

26.9

29.0

31.1

105.2

106.5

108.0

109.4

110.3

111.1

13.6

16.2

18.8

21.2

22.4

23.7

15.0

18.1

21.4

24.6

26.3

28.0

1.10

1.12

1.14

1.16

1.17

1.18

13.2

15.6

17.8

20.0

21.1

22.1

Calculation of Brine Volume

 

Expressing Salt Concentration (weight-by-weight)

 

 Expressing Salt Concentration (weight-by-volume)

 

Measuring Salt Concentration by Hydrometer. Hydrometer readings may be expressed as degree Baume (BE). The instrument is calibrated for densities between 1.00 (0Be) and 1.842 (66Be). The equation on the right will convert Baume readings to density:

 

Penetration in Cheese. The Dairy Processing Handbook cites the following information from the Danish Dairy Research Institute (Report No. 22).

Cheese curd is criss-crossed by capillaries; approximately 10,000 per cc. have been found. There are several factors that can affect the permeability of the capillaries and the ability of the salt solution to flow through them, e.g. since fat globules may block some of the capillaries, salt penetration will be delayed in cheese of high fat content.

The pH at the time of salting has considerable influence on the rate of salt absorption. More salt can be absorbed at low pH than at higher pH. However at low pH (<5.0), the body of the cheese is hard and brittle. At higher pH (>5.6), the body remains elastic.

 

The interrelationships between pH, calcium and sodium are important at the time of brining. Some parts of calcium are more available for ion exchange with sodium and the amount exchanged determines the body characteristics of the cheese. Milk contains about 1200 mg of calcium per liter. At the normal pH of milk, more than 90% of the calcium is bound in colloidal form to the casein micelles and less than 10% exists in ionised form . As the pH is lowered toward the isoelectric point of casein (4.6), the colloidal calcium is displaced from the micelles as the sites for binding become protonated.

The loosely bound calcium is sensitive to pH changes; the lower the pH the more calcium will leave the paracasein complex as hydrogen ions protonate the calcium sites. At salting these sites will not engage in exchange with sodium ions. Exchange takes place between sodium and calcium but not with the hydrogen ions.

If the pH of cheese curd before salting is in the high range (6.0-5.8), a considerable amount of calcium is still present in the paracaeinate. On brine treatment too much sodium will become attached to the casein through exchange with some of the calcium. This results in a softer cheese which may even lose its shape during ripening.

At the pH range 5.2-5.6 there is a balance between the calcium ions and hydrogen ions to bind the optimum amount of sodium to provide for a satisfactory body and texture.

At low pH (<5.2), too many sites are protonated and the sodium exchange becomes too small; therefore the body and texture of the cheese becomes too hard and brittle.

The higher the salt concentration of the brine, the more salt will be absorbed. At low concentrations (<16%), the paracasein swells and the surface will be smeary and slimy as the result of partial resolubilization. It is common to use salt concentrations near the saturation point (23%) at 10-14C.

The microbiological status of the brine must be kept under control . Certain salt- tolerant microorganisms can cause slimy surface, discoloration, and mouldiness. The risk of microbiological disturbances are greatest at low salt concentrations below 16%. Preparation of brine:
  1. Dissolve the salt directly in boiling water
  2. Add 0.1-0.2 % calcium chloride
  3. Cool to room temperature
  4. Adjust pH to 5.2-5.3 with HCl
  5. Monitor the salt concentration by refractometer readings and measure pH regularly and adjust if needed
  6. Avoid contaminations

Ripening of Cheese. With the exception of fresh cheese, all other cheese varieties go through a series of ripening processes involving microbiological, biochemical and physical changes to the product.

Lactose Decomposition. The moisture remaining in the curd after whey draining has the composition of the whey -- or diluted whey -- if water has been added for temperature adjustments. Lactose fermentation should be controlled in such a way that all lactose has disappeared no later than after pressing and prior to brine salting.

The different cheese making techniques take aim at controlling the lactic acid fermentation so that the pH of the curd at the time of salting is at the optimum level. - A Rule of Thumb: If the pH of the curd has not reached a level of 5.6 -  5.8 after 24 hours, the cheese will not be good.

The lactic acid which is produced is neutralized to a great extent in the cheese by the buffering components of the milk many of which are included in the coagulum. Lactic acid is thus present as lactates in the completed cheese. At a later stage , the lactates can provide substrate for the propionic bacteria which are an important part of the microbiological flora of Swiss cheese, including Emmenthal, Gruyere and similar types.

  • Cheese with Holes. Besides propionic acid and acetic acid, a considerable amount of carbon dioxide is formed, which is the direct cause of the large round "eyes" in these cheeses. The quality criterion for this characteristic is that the "eyes" must be uniformly distributed in the cheese mass.

  • The lactate in cheese can also be broken down by butyric acid bacteria. Butyric acid fermentation leads to accumulation of hydrogen in addition to volatile fatty acids and carbon dioxide.
Gassy defects in cheese are often a result of contamination by:
  • Coliform bacteria
  • Butyric acid bacteria

Protein Decomposition. The ripening of cheese is characterized by extensive proteolysis. The degree of protein decomposition affects the quality of the cheese in profound ways, particularly flavor and aroma but also body and texture. The changes are brought about by the enzyme systems of

Rennet is a proteolytic enzyme which coagulates milk by cleaving a specific bond in kappa-casein. However, prolonged action of rennet causes breakdown of paracasein into polypeptides. This attack serves as a preconditioning treatment for the subsequent action of the bacterial enzymes which decompose polypeptides faster than the intact paracasein. In cheese varieties, such as Swiss cheese, where the curd has been deliberately scalded, rennet has been destroyed, but the native proteases in milk can also hydrolyse paracasein into polypeptides, although at a slower rate.

Fat Decomposition. A number of mould-ripened cheese varieties, notably Camembert; Brie; Roquefort; and Stilton are characterized by extensive lipolysis.

Such cheese often have pronounced flavour and aroma from both proteolysis and lipolysis and the consumers are people who have acquired a taste for the exotic.

Growth of the highly aerobic mould mycelium is encouraged by stabbing heavy needles into the cheese cylinders to permit access of air (oxygen). When proper mould growth has developed along the needle marks, throughout the interior, all holes are sealed by oil or wax to limit oxygen.

 

 

The ripening process is characterized by pronounced lipolysis and the smell and aroma of volatile fatty acids. The Danish name for mould-ripened cheese is "Blue cheese" because of the particular colour of the mould against a white background. To achieve the correct hue, Danish cheese makers add chlorophyll as a complementary colour to the yellowish appearance of milk with a high fat content. Addition of chlorophyll to milk will give "blue cheese" a whiter background as a contrast for the blue-green mould

 

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