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 (e.g., low fat cheese) or imposed by government standards of identity. In Canada, standards of identity are defined for 46 cheese varieties (Table 11.1). 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.

1. 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 PF. The PF 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 by weight on the wet basis; and (2) the percent ratio of cheese fat to cheese total solids. This ratio is called “fat in the dry matter” or FDM. The FDM in cheese is determined mainly by PF 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 FDM decreases. The target value of FDM in the cheese can be used to determine the first approximation of the PF required in the milk to give the desired fat content of the cheese. See Table 11.1.

There is a third ratio, namely, casein number (CN), which we will not use in the standardization procedures given below, but which is important to understand. Total protein content of cow milk is about 3.3% of which about 2.6% is casein. The remainder is whey protein (about 0.7 %) including about 0.15% of nitrogenous compounds that 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 is better because the proportion of casein in total protein varies with breed, season, region and other factors. Helpfully, mid- and near-infrared milk analyzers can estimate casein. The percentage proportion of casein in total protein is referred to as the casein number (CN). The casein number in Ontario herds (which are predominately Holstein) averages about 77% and is positively correlated with total protein according to the following equation (Hill, Fulton, Melichercik, and Szijarto, 1998). Development of rapid direct casein testing in milk utilizing high speed IR technology, Technical Report to Agriculture and Food Laboratory Services, University of Guelph).

 Casein = (0.8302 x   crude protein) – 0.1990

Table 11.1: 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 regulation

Constants, Assumptions and Legend

1. All cheese composition and yield values are in units of percent by weight – including, both cheese and standardized milk. The calculations assume raw milk composition of 3.9% w/w fat and 3.2% w/w protein with subsequent standardization to specified PF ratios by removing cream.
2. Estimation of yield and protein/fat ratios are based on principles and yield equations described by D.B. Emmons, C.A. Ernstrom, C. Lacroix and P. Verret. J. Dairy Science 73(1990):1365.
3. 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.
4. 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” wash water at temperature less than 20ºC 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 – 80ºC) 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.

2. Factors Affecting Standardization

Standardization normally means adding skim milk or skim milk solids, or removing cream to increase the PF. Several practical points are relevant.

• Multiple component pricing makes it possible to cost milk components as individual ingredients. PF can then be optimized according to relative costs of protein and fat, transfer rates of protein and fat from milk to cheese, and the value of fat in the cheese relative to its value as cream.
• Component yield economies must be balanced against cheese quality.
• Calculation of PF to produce cheese with required moisture and fat depends on the retention of fat, casein, and serum solids in the cheese, where serum solids refers to recovery of the soluble components of milk, namely, sugars, whey proteins, non-protein nitrogen and some minerals. Specifically, the important principles with respect to serum solids are:
  • Higher serum solids recovery means that a lower PF is required (that is more fat or less protein) in the cheese milk to achieve the target FDM in the cheese.
  • Serum solids recovery is increased in high moisture cheese because the moisture retained includes dissolved solids.
  • Serum solids recovery is reduced by curd washing treatments.
  • Serum protein (whey protein) recovery is increased by milk pasteurization.

3. Sources of Milk Solids

Sources of Protein other nonfat solids

Standardization usually requires the addition of protein or removal of fat. The former has the advantage that it is possible to produce cheese quantities beyond what is possible from the available fresh milk. This is significant in areas where fresh milk is in short supply or as in Canada, where milk purchases are limited by quotas. Several sources of milk proteins are available for cheese milk standardization.

1. Skim milk powder is convenient for small or remote cheese plants. It can be used effectively with the following limitations:
   • Use only certified LOW HEAT (Whey Protein Index > 6) and antibiotic free powders.
   • Reconstitute the powder thoroughly and filter to remove undissolved particles before blending with the cheese milk. Incomplete solubilization may cause over set Swiss cheese and poor stretching of pasta filata cheese.
   • Non-fat solids of cheese milk should not be raised above about 11% (normal level is 9%). This can be avoided by adding more water with the powder.
2.  Skim milk and condensed milk are convenient sources because they can be handled and measured in liquid form. The only cautions are to limit heat treatment to minimum pasteurization requirements and limit non-fat milk solids to less than 11 Kg/100 Kg. Again, non-fat solids can be adjusted by adding water.
3. Culture media contribute non-fat milk solids that must be accounted for in calculations for milk standardization. For example, the high heat treatment involved in bulk culture preparation ensures that most milk proteins (including whey proteins) present in the culture will be transferred to the cheese.
4. Protein concentrates and isolates available to supplement cheese milk are numerous. A few are listed below. The feasibility of using one or more of these products depends on, among other things, the type of cheese. For example, relative to most other varieties, high levels of whey proteins can be used in Feta cheese without compromising quality.
   • Liquid or dried milk concentrates prepared by ultrafiltration of skim milk contain caseins and whey proteins in the normal proportions found in milk.
   • Specially prepared blends of caseins and whey proteins.
   • Liquid or dried casein concentrates prepared by microfiltration of skim milk.
   • Sodium or hydrogen caseinates, which are usually prepared from rennet casein.
   • Liquid concentrates of denatured whey proteins (Centri-whey process).
   • Microparticulated whey proteins, which can be used to replace or extend caseins and also as fat replacers in low fat cheeses.

In Canada, sources of casein used in cheese making have been regulated to reduce imports of alternate sources of casein. The Canadian Food and Drug Regulations now restrict the use of casein in powdered forms. It also limits the use of whey proteins in cheese. Regulation B.08.033 (a) states:

[Cheese shall] except for feta cheese, have a casein content that is derived from milk or from ultrafiltered milk, partly skimmed milk, ultrafiltered partly skimmed milk, skim milk, ultrafiltered skim milk or cream, rather than from other milk products, that is at least the following percentage of the total protein content of the cheese, namely,

(A) 63 per cent in the case of Pizza Mozzarella cheese and Part Skim Pizza Mozzarella cheese,

(B) 83 per cent, in the case of Brick cheese, Canadian Style Brick cheese, Canadian Style Muenster cheese, Colby cheese, Farmer’s cheese, Jack cheese, Monterey (Monterey Jack) cheese, Mozzarella (Scamorza) cheese, Part Skim Mozzarella (Part Skim Scamorza) cheese, Part Skim Pizza cheese, Pizza cheese, Skim milk cheese and any other variety of cheese not referred to in clause (A) or (C), and

(C) 95 per cent, in the case of any other variety of cheese named in the table to this section,

(i.2) have a whey protein to casein ratio that does not exceed the whey protein to casein ratio of milk.

The liquid casein minimum for Cheddar is also 83% as set out in B.08.034 (a).

Sources of Milk Fat

Most jurisdictions prohibit the use of non-dairy fat in cheese. That leaves a number of choices:

• Milk and cream unaltered other than by pasteurization and gravity or centrifugal creaming.
• Recombined cream prepared from skim milk and butter oil. This process requires homogenization which is undesirable for cheese with some exceptions including Feta, Blue and cream cheese. According to some reports, quality problems associated with homogenization are reduced by homogenizing the cream rather than the milk.

In cases where non-dairy cream is desirable, the limitations are:

• Altered flavour, especially the absence of short chain fatty acids such as butyric that are found only in dairy fat. The flavour problem can be addressed by dairy flavour additives.
• Preparation of filled cheese milk (filled means containing fat other than dairy fat) requires homogenization, which as noted above, normally creates inferior texture.
• The fat should have melting properties similar to butter fat.

Recombined Milk

Considering the limitations described above for protein and fat sources, it is possible to manufacture cheese from recombined milk.

4. Types of Standardization

Manual Standardization

In the absence of online systems equipped with customized algorithms, it is necessary to create spreadsheets to calculate milk formulae and monitor yield parameters. The first step is to determine the optimum PF, a process that always involves some experimentation. The estimates given in Table 6.1 can be used for a first approximation and then adjustments can be made on succeeding days based on the cheese analysis. This emphasizes the need for consistent and accurate records of milk and cheese composition and manufacturing parameters.

Automated Standardization

Automated composition control systems separate warm milk into cream and skim and then automatically and continuously recombine the two streams in the proportion required to obtain the desired PF ratio. The standardized milk is tempered to the correct setting temperature and delivered directly to the setting vats. Two general types of control are possible.

• Fully automated using online milk analysers based on near infrared, density measurement, or light scattering technology.
• Partially automated control where composition is monitored with an off line milk analyzer.

5. 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 Kg 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 analyzer is not available the protein content of pooled milk can be crudely estimated from the fat content using the following formula:

% protein = (0.4518 x %fat) + 1.521

For the purpose of this example, assume the fat content of the available fresh milk is 3.50 Kg/100 Kg and the protein is  3.10 Kg/100 Kg. For simplicity we’ll switch to weight/weight percentages for the rest of this example and elsewhere unless otherwise stated.

Step 2: Determine the required fat, moisture and FDM of Cheddar cheese. ‘Dairy Products Regulations’ of the Canada Agricultural Products Standards Act require Cheddar cheese to contain a minimum of 30.0% fat and a maximum of 39.0% moisture. Therefore,

Step 3: Determine the required PF of the milk. The PF required to yield FDM = 50% as required for Cheddar cheese is about 0.96. See Table 6.1.

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

1. Calculate the % protein required to give PF = 0.96

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

2. The protein to be added = 3.36 ‑ 3.10 = 0.26%
3. Calculate the weight of protein which must be added per 10,000 kg of milk.

     The required weight of protein = 0.26% of 10,000 Kg  = 26.0 kg

4. 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.

    The required amount of powder = 26.0/0.35 = 74.0 kg

    5. Check calculations:

Weight of Fat in Milk	3.5% of 10,000 Kg = 350.0 kg
Weight of Protein in Milk	3.1% of 10,000 Kg = 310 kg
Weight of Protein in SMP	35% of 74 Kg = 26.0 kg
Total Protein
PF Ratio of Standardized Milk

Standardization by Removing Fat

1. Calculate the level of fat required to give PF = 0.96
The required level of fat = percent protein / 0.96 = 3.1 /0.96 = 3.23 %

2. Use a Pearson’s square to calculate the weight of cream that must be removed, assuming that the separator removes cream containing 30% of fat.

Unstandardized Milk 3.50%
	Standardized Milk 3.23%
Cream 30.00%
	Total Parts

This means that the required proportions of cream and standardized milk are 0.27 and 26.50 parts, respectively, for a total of 0.27 + 26.77 = 27.04 parts. On a percent basis, the components are:

3. Calculate how much 30% cream must be removed from 10,000 Kg of milk to provide standardized milk containing 3.23% fat.

4. Check calculations:*

In this calculation, we have directly accounted for the protein in the cream based on the protein in the serum of the milk and in the cream. The idea is we assume that all the protein is in the serum, that is, the total milk or cream minus the fat. That’s not quite true because there is some protein in the fat globule membrane, but it’s close enough to check the calculations. We know the fat and protein content in the original milk, so we can calculate the protein in the milk serum by multiplying the protein content of the milk by the ratio of 100/(100-milk fat).  Because  the protein in the serum of the milk and cream are the same, we can then calculate the protein of the cream by multiplying the protein of the serum by the ratio (100 – cream fat)/100.

5. 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.

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.

1. 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 2 in the Standardizing by Removing Fat section.

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:

2. Calculate the amount of skim and fresh milk required.

3. Check:

Addition of Cream

The natural PF 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 PF = 0.96 and make a full fat cheese with FDM = 50%. When the required FDM is less than 50%, it is unlikely that fat would have to be added to the milk. 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.

Units

Raw milk composition for payment purposes is reported in units of kg of component per hL of milk at 4ºC. 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) measurements (e.g., kg component per 100 kg of milk) result in smaller values when expressed as w/v  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 analyzers report composition in units of w/w; and (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 load cells on farm bulk tanks, which are expensive to install and maintain.

In cheese making, it is also more convenient to use volumetric meters to measure milk while filling cheese vats; however, cheese has to be weighed so it’s preferable to convert milk volume to weight and report milk composition in units of w/w rather than w/v. This allows yields to be reported and analyzed in units of w/w, that is weight of cheese per weight of milk. This means that milk volume needs to be converted to weight either before or after it’s in the vat. This can be done by multiplying milk volume by milk density. For example, 1,000 L of milk with density of 1.0350 Kg/L would equal 1.035 kg. Similarly, composition expressed as % w/v can be converted to w/w units by dividing by density (e.g., given density or 1.0350, 4.0 kg/ hL of milk equals 3.86 kg/100 kg or simply 3.86% w/w.

For simplicity and clarity, in this E-book we’ll use units of percent w/w unless otherwise specified. For examples,  30% fat in Cheddar cheese means 300 g fat per kg cheese). Similarly, 3.3% fat in milk means 3.3 kg of fat per 100 kg milk. When weight-over-volume units are used, the specific units are given, e.g., 3.3 kg/hL.

Note: that the density (ρ_T) 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 in liters at 32ºC, in order to convert liters to Kg, you need to know the density of the milk at 32ºC. For milk of average composition (4.0 % fat), the density can be estimated according to the following equation^[1].

ρ_T = 1.0366 -0.00035T,  where ρ_T is density at Temperature T

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

6. General Guidelines for Standardization

1. Determine the present composition of your cheese.
2. Determine the fat and protein content of milk accurately and daily.
3. Measure milk volume or weight accurately and keep accurate records.
4. 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.
5. Weigh accurately the weight of powder or skim milk added or the weight of cream to be removed.
6. Determine the composition of the standardized cheese and if necessary adjust the proportions of fat and protein in the cheese milk on succeeding days.
7. If bulk starter is being added, reduce the amount of protein added by the amount of protein in the culture.
8. 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.
9. Without sophisticated meters, 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 PF ratio by adding skim solids or cream as required.
10. 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.
11. Be careful to use the correct units when calculating, weighing and metering.