Standardization of milk for cheese making

Standardization refers to the practice of adjusting the composition of cheese milk to maximize economic return from the milk components while maintaining both cheese quality and cheese composition specifications. Composition specifications may be self imposed (eg., low fat cheese) or imposed by government standards of identity. In Canada, standards of identity are defined for 46 cheese varieties. These standards only include limits for maximum moisture and minimum fat so they do little to standardize other cheese characteristics. For example, American Mozzarella is made by a different process and has different properties than Italian stretch Mozzarella, but by Canadian regulations American Mozzarella can be called Mozzarella provided it contains less than 52% moisture and more than 20% fat.

Table 6.1.  Some cheese varieties with some characteristics, composition and suggested ratio of protein/fat in standardized  milk. 

Fat and moisture levels for most varieties correspond to definitions given in Canadian regulations.

 

 

 

 

 

Cheese Target Composition

Milk

Yield

 

Texture

Washing

Salting

Rind

Fat

Moist

FDM

MNFS

Prot/Fat

% w/w

Alpina (Stella Alpina)

Semi-soft

Maybe warm

B or DS

Smear

27

46

50.0

63.0

0.90

11.5

Asiago

Firm to hard

None

B

Dry

30.0

40.0

50.0

57.1

0.93

10.1

Baby Edam

Firm

Warm wash

B

None

21.0

47.0

39.6

59.5

1.56

8.7

Baby Gouda

Firm

Warm wash

B

None

26.0

45.0

47.3

60.8

1.15

9.7

Blue

Soft to semi-soft

None

DC&DS

Smear or none

27.0

47.0

50.9

64.4

0.87

11.9

Bra

Firm to hard

None

B or DS

Dry

26.0

36.0

40.6

48.6

1.40

7.6

Brick

Semi-soft to firm

Usually warm

DC or DS

Smear or none

29.0

42.0

50.0

59.2

1.04

9.7

Brie

Soft

No

DS

Mould

23.0

54.0

50.0

70.1

0.86

14.0

Butterkase (Butter)

Semi-soft

Maybe warm

B

Smear

27.0

46.0

50.0

63.0

0.90

11.5

Caciocavallo

Firm to hard

Hot Stretch

B

Dry

24.0

45.0

43.6

59.2

1.17

9.8

Camembert

Soft

None

DS

Mould

22.0

56.0

50.0

71.8

0.86

14.7

Canadian Muenster

Semi-soft

Maybe warm

B or DS

Smear

27.0

46.0

50.0

63.0

0.90

11.5

Cheddar

Firm

None

DC

None

31.0

39.0

50.8

56.5

0.91

10.0

Cheshire

Firm

None

DC

None

30.0

44.0

53.6

62.9

0.79

11.9

Colby

Firm

Cold wash

DC

None

29.0

42.0

50.0

59.2

1.03

9.7

Coulommiers

Soft

None

DS

Mould

22.0

56.0

50.0

71.8

0.85

14.8

Danbo

Firm, small eyes

None

B,DS or DC

Smear or none

25.0

46.0

46.3

61.3

1.04

10.6

Edam

Firm

Warm wash

B

Dry or none

22.0

46.0

40.7

59.0

1.50

8.7

Elbo

Firm

None

DS or B

Dry or none

25.0

46.0

46.3

61.3

1.04

10.6

Emmentaler

Firm with eyes

None

B

Dry or none

27.0

40.0

45.0

54.8

1.13

9.1

Esrom

Semi-soft

Maybe warm

DS or B

Smear

23.0

50.0

46.0

64.9

1.04

11.5

Farmers

Firm

Cold wash

DC

None

27.0

44.0

48.2

60.3

1.11

9.7

Feta

Soft

None

DS

None

22.0

55.0

48.9

70.5

0.90

14.0

Fontina

Semi-soft to firm

Maybe warm

DS or B

Light smear

27.0

46.0

50.0

63.0

0.90

11.5

Fynbo

Firm,small eyes

?

B or DC

Dry

25.0

46.0

46.3

61.3

1.05

10.5

Gouda

Firm, small eyes

Yes

B

None

28.0

43.0

49.1

59.7

1.07

9.7

Guyere

Firm, eyes

No

B&DS

Light smear

28.0

38.0

45.2

52.8

1.14

8.7

Havarti

Semi-soft

Warm wash

B or DS

Smear or none

23.0

50.0

46.0

64.9

1.19

10.5

Jack

Semi-soft

Cold wash

DC

None

25.0

50.0

50.0

66.7

1.02

11.4

Kasseri

Firm to hard

Hot stretch

B

Dry

25.0

44.0

44.6

58.7

1.13

9.8

Limburger

Soft to semi-soft

Maybe warm

DS or B

Heavy smear

25.0

50.0

50.0

66.7

0.88

12.6

Maribo

Firm, small eyes

None

B or DS

Dry or none

26.0

43.0

45.6

58.1

1.09

9.8

Montasio

Firm

Usually warm

DS or B

Dry

28.0

40.0

46.7

55.6

1.19

8.7

Monterey

Firm

Cold wash

DC

None

28.0

44.0

50.0

61.1

1.04

10.0

Mozzarella (Italian)

Semi-soft to firm

Hot stretch

B

None

20.0

52.0

41.7

65.0

1.22

11.1

Mozzarella (Canadian)

Firm

Cold wash

DC

None

20.0

52.0

41.7

65.0

1.22

11.1

Muenster

Semi-soft

Maybe warm

B or DS

Light smear

25.0

50.0

50.0

66.7

0.88

12.6

Parmesam

Hard, grating

None

B&DS

Dry

22.0

32.0

32.4

41.0

2.02

6.1

Part Skim Mozz

Semi-soft to firm

Hot stretch

B

None

15.0

52.0

31.3

61.2

1.90

9.1

Part Skim Pizza

Semi-soft to firm

Hot stretch

B

None

15.0

48.0

28.8

56.5

2.20

7.9

Pizza

Semi-soft to firm

Hot stretch

B

None

20.0

48.0

38.5

60.0

1.42

9.5

Provolone

Firm

Hot stretch

B

None

24.0

45.0

43.6

59.2

1.17

9.8

Romano

Hard

None

B&DS

Dry or none

25.0

34.0

37.9

45.3

1.58

7.0

Samsoe

Firm, few eyes

None

B&DS

Dry or none

26.0

44.0

46.4

59.5

1.05

10.1

Tilsiter (Tilsit)

Firm

Usually warm

B or DS

Smear or none

25.0

45.0

45.5

60.0

1.08

10.2

Tybo

Firm, few eyes

None

B

Dry or none

25.0

46.0

46.3

61.3

1.04

10.6

                       

 

CONSTANTS,  ASSUMPTIONS AND LEGEND

1.  All cheese composition and yield values are in units of percent by weight--including both cheese and standardized milk.

2.  Estimation of yield and protein/fat ratios are based on principles and yield equations described by D.B. Emmons, C.A. Ernstrom, C. Lacrois and P. Verret.  J. Dairy Science 73(1990):1365.

3.  Calculations based on fresh milk of 3.90% fat and 3.20% protein and assuming standarization was by removing 35% cream from the same fresh milk

4.  Whey solids in moisture was assumed to be 6.5% except for washed types when a value of 3.2% was used.  For the purpose of yield calculations, pasta filata types (hot stretch) were considered to be unwashed.  75% of cheese moisture was considered available as a solvent for whey solids.

5.  Conversion factors:

Proportion of fat transferred from milk to cheese was   0.93

Amount of casein + minerals transferred to cheese was  casein x 1.018

Casein number was 76.5

Washing:

'warm' means washing at temperatures near normal cooking temperatures (32-40oC)

'cold'  means wash water at  temperature less than 200C is used to wash and cool the curd

'maybe warm'   means that the cheese may or may not be washed with warm water

'hot stretch' means the cheese is heated and worked in hot water (70-800C) as in Pasta Filata types.

Salting:  B = brine salted;  DS = dry salted on cheese surface;  DC = curd dry salted before hooping.

FDM = fat as percentage by weight of cheese solids;    MNFS = moisture as percentage of non-fat substance in cheese.

Prot/Fat  = ratio of protein to fat in standardized cheese milk.

Important parameters of composition

Standardization of cheese milk normally requires increasing the proportion of protein relative to fat, which can be done by adding protein or taking away fat. The relative amount of protein and fat in milk is called the protein-fat ratio or P/F. The P/F is the principal factor which determines the amount of fat in the cheese relative to other milk solids in the cheese. Because it is easy to measure cheese fat and total solids, the proportion of fat in the cheese is reported as (1) fat on a wet basis; and (2) the ratio of cheese fat to cheese total solids. This ratio is called 'fat in the dry matter' or F/DM. The F/DM in cheese is determined mainly by P/F of the milk but the percent moisture is also important. Because cheese whey contains soluble solids, higher cheese moisture means that more soluble solids (mostly non-fat solids) are also retained in the cheese so that the ratio of F/DM decreases. The target value of F/DM in the cheese is used to determine the first approximation of the P/F required in the milk to give the desired fat content of the cheese. 

There is a third ratio, namely, casein number (CN), which we will use in the standardization procedures given below, but which is important to understand. Total protein content of cows' milk is about 3.3Kg/hL of which about 2.6 /Kg/hL is casein. The remainder is whey protein (about .7 Kg/hL) including about .1 Kg/hL of some nitrogenous compounds which are not true protein and are referred to collectively as non-protein nitrogen (NPN). Casein is mostly recovered in cheese (i.e., transferred from milk to cheese during cheese manufacture). Whey proteins remain soluble in whey so that only small amounts are recovered depending on how much whey is retained in the cheese. Casein content is, therefore, most relevant to cheese yield, so when cheese makers standardize milk on the basis of protein content, they are using total protein as an index of casein content. Direct measurement of casein would be better because the proportion of casein in total protein varies with breed, season, region and other factors. However, wet chemical analysis of casein is not feasible for most plants and rapid instrumental methods are still under development.

The percentage proportion of casein in total protein is referred to as the casein number (CN). 

Methods of Standardizing

There are three methods of standardizing milk, namely:

  1. Addition of concentrated non-fat milk solids (i.e., skim milk powder or condensed skim).
  2. Addition of skim milk.
  3. Removal of cream.

These methods are based on the assumption that the milk has a high fat content relative to the protein content. This is normally the case, so that cows' milk usually has excess fat over that required to produce a legal cheese. The exceptions are high fat cheese such as cream cheese or double cream blue cheese.

It is not always economical to standardize milk. The cheese maker must compare the costs of standardizing with the extra yield of cheese or cream. Many cheese makers simplistically assume that all they have to do is standardize milk to meet the official composition standards. But the objective of standardization is to maximize the total return from all milk components while meeting regulations and without compromising quality. If the value of butter fat is low relative to protein, it is more economical to sell the fat as cheese rather than as cream provided that the extra fat can be retained in the cheese without compromising quality.

Units

Raw milk composition for payment purposes is reported in units of Kg of component per hL of milk at 4C. This is referred to as weight over volume (w/v) measurement. Measurement in units of w/v is dependent on milk density which in turn is affected by both composition and temperature. Weight over weight (w/w) measurement (eg., Kg component per 100 Kg of milk) results in a significantly smaller value because the density of milk is more than 1 Kg/L. Measurement by w/w has the advantages that: (1) most wet chemical reference analyses used to calibrate milk analysers report composition in units of w/w; (2) w/w values are independent of milk temperature. However, milk composition for payment purposes is reported in units of w/v because the volume of milk is easily measured with dip sticks or volumetric meters. Weight measurement would require installation of farm bulk tanks on expensive load cells. Volume rather than weight measurement of milk and other liquids is also more convenient in the plant.

In any case, the important point with respect to accurate standardization is to ensure that all measurements and calculations use the correct units. When component estimates are given as percentages, the basis of measurement must be stated as w/w percent (eg., Kg fat per 100 Kg milk) or w/v percent (eg., Kg fat/hL of milk). In this manual composition values given in percent always mean w/w. Cheese composition will always be stated in percent w/w (eg., 30% fat in Cheddar cheese means 300 g fat per Kg cheese). Similarly, 3.3 % fat in milk means 3.3 Kg fat per 100 Kg milk. If weight over volume units are used I will always state the specific units, eg., 3.3 Kg/hL. Because composition of producer milk is reported to processors in units of Kg/hL and because milk metering systems are volumetric, I will usually report milk composition in units of Kg/hL.

It is important to ensure that milk analysers are calibrated in the appropriate units and the correct units are subsequently used for milk standardization calculations and calibration of automated standardizing systems. Wet chemical analysis is normally done by weight, so reference results for milks used to calibrate milk analysers are normally reported in units of percent by weight and it is convenient to calibrate milk analysers in percent by weight (eg., Kg/100 Kg). If required, w/v values can be estimated using the following equation.

w/v=w/w x pT where pT is density at temperature T

Note, that the density must be known at the given temperature. For example, if the milk composition was given in units of w/w and you are metering milk into your cheese vat at 32C you need to know the density of the milk at 32C. For milk of average composition (4.0 % fat), the density can be estimated according to the following equation(1).

pT = 1.0366 - .00035T where pT is density at temperature T

Density values for milk of average composition (4% fat) at some temperatures relevant to cheese manufacture are:

Calculations

The following steps are required to calculate the amount of powder or skim milk to be added, or the amount of cream to be removed. Suppose a cheese maker wishes to fill a 10,000 l (100 hl) setting vat for the manufacture of Cheddar cheese.

Step 1. Determine the protein and fat contents of the milk using an automatic milk analyzer. If a milk analyser is not available the protein content of pooled milk can be crudely estimated from the fat content using the following formula:

Kg/hL of protein = (0.4518 x Kg/hL of fat) + l.521

For the purpose of this example, assume the available milk contains 3.50 Kg/hL of fat and 3.l0 Kg/hL of protein.

Step 2. Determine the required fat, moisture and F/DM of Cheddar cheese. 'Dairy Products Regulations' of the Canada Agricultural Products Standards Act require Cheddar cheese to contain a minimum of 31% fat and a maximum of 39% moisture. Therefore,

FDM = % fat/% dry matter = 30.0/(100.0 - 39.0) = 49.2%

Step 3. Determine the required P/F of the milk. The P/F required to yield F/DM = 50% as required for Cheddar cheese is about 0.96.

Step 4. Calculate the amount of: skim milk powder to be added; or fat to be removed; or skim milk to be added.

Standardization by Adding skim milk powder

(i) Calculate the % protein required to give P/F = 0.96

The required level of protein = 0.96 x % fat = 0.96 x 3.50 = 3.36

(ii) The % protein to be added = 3.36 - 3.10 = 0.26 Kg/hL

(iii) Calculate the weight of protein which must be added per 100.00 hL of milk.

The required weight of protein = 0.26 Kg/hL x 100 hL = 26.0 Kg

(iv) Calculate the amount of powder which must be added assuming the skim milk powder (SMP) contains 35.0% protein. If possible the skim powder should be analyzed so the exact protein content is known. The supplier may be able to provide this information. Protein content can also be estimated using a milk analyzer to test the reconstituted skim milk.

Required amount of powder = 26.0 Kg/0.35 = 74.3 Kg

(v) Check calculations:

Weight of fat in milk: 3.50 Kg/hL x 100.00 hL = 350.0 Kg.
Weight of protein in milk: 3.10 Kg/hL x 100.00 hL = 310.0 Kg
Weight of protein in SMP: 0.35 Kg/Kg x 74.0 Kg = 26.0 Kg
Total Protein: 310.0 Kg + 26.0 Kg = 336.0 Kg
P/F ratio of standardized milk: 336.0 Kg/350.0 Kg = 0.96 

Standardization by Removing fat

(i) Calculate the level of fat required to give P/F = 0.96.

The required level of fat = Kg/hL of protein/.96 = 3.10 Kg/hL/.96 = 3.23 Kg/hL

(ii) Use a Pearson's square to calculate the litres of cream that must be removed, assuming that the separator removes cream containing 30.00 kg/hl of fat.

Un-standardized Milk
3.50 Kg/hL
  30.00 - 3.23 = 26.77 Parts
Stanrdardized Milk
  Standardized Milk
3.23 Kg/hl
 
Cream
30.00 Kg/hL
  3.50 - 3.23 = 0.27 Parts
Cream
  Total Parts 26.77 + 0.27 = 27.04

This means that the required proportions of cream and fresh milk are 0.27 and 26.77 parts, respectively, for a total of 0.27 + 26.77 = 27.04 parts. On a percent basis, the components are:

Standardized Milk 100 x 26.77/27.04 = 99.0% w/v
30% cream 100 x 0.27/27.04 = 1.00% w/v

(iii) Calculate how much cream must be removed from 10,000 Kg of milk to provide standardized milk containing 3.23% fat. 

Cream to be removed = 1.00% of 100 hL = 1.00 hL.

(iv) Check calculations:

Weight of fat in milk 3.50 Kg/hL x 100.00 hL = 350.0 Kg
Minus fat in cream 30.00 Kg/hL x 1.00 hL = 30.0 Kg
Weight of fat in standardized milk 350.0 Kg - 30.0 Kg = 320.0 Kg
Net volume of milk 100.00 hL - 1.00 hL = 99.0 hL
Weight of protein 3.10 Kg/hL x 99.0 hL = 306.9 Kg
Protein/fat ratio 306.9/320.0 = 0.960

(v) Adjust the final weight for the quantity of cream removed. If you wish to fill the vat completely sum the vat capacity and the initial estimate of the cream to be removed and recalculate the required amount of cream.

Approximate total volume of fresh milk: 100.00 hL + 1.01 hL = 101.01 hL.
Weight of cream to be removed 1.00% of 101.01 hL = 1.01 hL
Final volume of standardized milk 100.00 hL - 1.01 hL = 99.99 hL

Standardization by Adding skim milk

The following calculation is based on the assumption that the protein content of the skim milk is the same as the protein content in the skim portion of the fresh milk to be standardized. This is exactly true only when the skim milk is derived from the same source as the fresh milk.

(i) Use a Pearson square to determine the relative proportions of skim milk and milk required to yield a fat content of 3.23% as calculated in Step B above. 

Skim milk
0.10 Kg/hL
  3.5 - 3.23 = 0.27 Parts
Skim Milk
  Standardized Milk
3.23 Kg/hl
 
Unstandardized Milk
3.50 Kg/hL
  3.23 - 0.10 = 3.13 Parts
Unstandardized Milk
  Total Parts 0.27 + 3.13 = 3.40

This means that 0.27 parts of skim are required for 3.13 parts of milk where the total mixture consists of 0.27 + 3.13 = 3.40 parts. On a percent basis, the mixture is: 

Skim milk 100 x 0.27/3.4 = 7.9%
Unstandardized Milk 100 x 3.13/3.4 = 92.1%

(ii) Calculate the amount of skim and fresh milk required. 

Weight unstandardized milk 92.1% of 100 hL = 92.10 hL.
Weight of 0.1% skim milk 7.9% of 100 hL = 7.90 hL.

(iii) Check:

Weight of fat in unstandardized milk 3.50 Kg/hL x 92.10 hL = 322.4 Kg
Weight of fat in skim milk 0.10 Kg/hL x 7.90 hL = 0.80 Kg
Total fat 322.4 Kg + 0.8 Kg = 323.2 Kg
Weight of Protein 3.10 Kg/hL x 100 hL = 310.0 Kg.
Protein/fat ratio 310.0/323.2 = 0.959

Addition Of Cream

The natural P/F of milk is higher in low fat milk. In practice, this means that when the milk fat is less than 3.0%, it may be necessary to add fat to obtain P/F = 0.96 and make a full fat cheese with F/DM = 50%. When the required F/DM is less than 50%, it is unlikely that fat would have to be added to the milk. The natural P/F is also high in the fall and early winter so fat may have to be added for full fat cheese at these times. Some cheese such as double cream Blue or double cream Havarti may also require addition of fat. Given the fat content of available cream, a Pearson's square can be used to calculate the amount of cream required in a similar manner to the examples given above.

General Guidelines for Standardization

  • Determine the fat and protein content of milk accurately and daily.
  • Measure milk volume or weight accurately and keep accurate records. 
  • If powder is being added, use only high quality, low temperature, antibiotic free powder of known protein content. Low temperature powder is required to ensure that excessive denaturation of whey proteins in the powder will not impair milk coagulation and/or cause texture defects in the cheese. To ensure low temperature powder, ask your supplier to certify a whey protein nitrogen index (WPI) greater than 6.0. 
  • Weigh accurately the weight of powder or skim milk added or the weight of cream to be removed. 
  • Determine the composition of the standardized cheese and if necessary adjust the proportions of fat and protein in the cheese milk on succeeding days. 
  • If bulk starter is being added reduce the amount of protein added by the amount of protein in the culture. 
  • The maximum recommended level of skim milk solids in cheese milk is 11%. Normal milk contains about 9% skim solids so the maximum level of additional skim solids is 2%. If standardization requires more it is recommended to standardize by removing fat or adding skim milk rather than by adding skim milk powder. Another alternative is to add some powder and then complete standardization by removing cream or adding skim milk. 
  • Without sophisticated metering equipment it is difficult to obtain exact standardization. Provided you have a milk analyser, you can do a final check of milk composition after the milk is in the vat and then 'fine tune' the P/F ratio by adding skim solids or cream as required. 
  • It is not possible to predict the exact composition of the finished cheese. However, when manufacturing conditions and milk composition are the same from day to day, it is possible to predict the composition of cheese with greater accuracy and the proportions of fat and protein in the cheese milk can then be 'fine-tuned' accordingly. It is, therefore, important to keep accurate records. 
  • Be careful to use the correct units when calculating and weighing and metering.