Standardization of cheese milk composition

In addition to standardization of microflora, it is normally necessary to adjust milk fat or protein or both. The objective of milk composition standardization is to obtain the maximum economic return from the milk components. In practice, this means that milk composition is adjusted to achieve the most economically favourable balance of the cost of ingredients and the percent transfer of milk solid components to cheese while maintaining cheese quality.

Cheese yield is mainly determined by the recoveries of protein and fat in the cheese (that is the percent of fat and protein transferred from milk to cheese) and by cheese moisture, but other components also contribute significantly. Cheese yield is discussed in Yield efficiency. Standardization of milk for cheese making is a detailed practical guide to milk standardization, including the necessary calculations for manual standardization. Here we summarize general considerations on milk standardization. 

Government standardized cheese varieties

Food regulatory agencies in many jurisdictions have mandated standardized foods for which specific criteria with respect to composition and/or quality must be met. Section 28 Table Part 1, Canada Agricultural Products Act and Regulations lists maximum moisture and minimum fat levels (percent by weight) for 46 cheese varieties. No other composition or quality standards are prescribed, so, the identities of cheese varieties are not protected. For example, American mozzarella is NOT pasta filata cheese like Italian stretch mozzarella, but it is mozzarella according to Canadian regulations. 

Cheese fat on a dry matter basis

Table 6.1 includes data for target fat and moisture content according to the respective minimum and maximum values as prescribed by the Canada Agricultural Products Act. It also includes a column for fat in the dry matter (FDM) which is the target cheese fat content reported as a percentage of the target total solids content, where total solids is calculated as 100 minus the target moisture content. Because the principal nonfat component in cheese is casein, the target FDM value is useful to estimate the proportions of fat and protein required in the cheese milk. For example cheese makers generally consider a full fat cheese contains 50% FDM which corresponds to a protein fat ratio in the cheese milk of 0.94 - 0.96. By this criteria, both Cheddar and Feta are full fat cheese because they both contain about 50% FDM, although on a wet basis their respective fat contents are 31 and 22%. 

Protein/fat ratios (P/F)

P/F (ratio of protein to fat) is exactly what the name implies. Having no units, it is an index of the relative proportions of fat and protein in the milk. Please be clear that the P/F value indicates nothing about the absolute value of fat and protein. P/F ratio is generally lower in low fat milk and higher in high fat milk, so that Jersey milk, for example, has a less favourable P/F for cheese making than Holstein milk. This is partially offset by a higher casein number (casein as a percentage of total protein) in Jersey milk. 

Standardizing to target protein/fat ratios

Standardization normally means adding skim milk or skim milk solids, or removing cream to increase the ratio of protein to fat (P/F). Several practical points are relevant.

• Multiple component pricing makes it possible to cost milk components as individual ingredients. P/F 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 P/F to produce cheese with required moisture and fat depends on 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, nonprotein nitrogen and some minerals. Specifically the important principles with respect to serum solids are:
  • Higher serum solids recovery means that a lower P/F 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 (there is more discussion on heat treatments in the next section).

Standardizing to casein/fat ratios

Better process and composition control can be achieved by standardizing to fixed casein/fat ratios rather than protein/fat ratios. This requires accurate casein measurement which is still not feasible for most plants. See further discussion in Standardization of milk for cheese making and Yield efficiency. 

Sources of milk proteins

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's 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.
• Nonfat 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.
• Protein from skim milk powder is usually more expensive than from other sources.

(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 nonfat milk solids to less than 11 kg/100 kg. Again, nonfat solids can be adjusted by adding water. 

(3) Culture media contribute nonfat milk solids which 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 ultra filtration 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.
• Liquid concentrates of denatured whey proteins.

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 generally considered undesirable with some exceptions including Feta, Blue and cream cheese. According to some recent work quality problems associated with homogenization can be eliminated by homogenizing the cream rather than the milk. Homogenization of cheese milk is further discussed in Section 5.4 below.

In cases where nondairy cream is desirable, the limitations are:

• Altered flavour, especially the absence of short chain fatty acids such as butyric which are only found 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 normally creates inferior texture.
• The fat should have melting properties similar to butter fat.

Manual standardization

In the absence of online systems equipped with customized algorithms, it is necessary to create spread sheets to calculate milk formulae and monitor yield parameters. The first step is to determine the optimum P/F, 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.

Detailed procedures, including calculations, for manual standardization are described in Standardization of milk for cheese making.

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 P/F 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 infra red or light scattering technology.
• Partially automated control where composition is monitored with an in line density metre which is calibrated using an off line milk analyser.

Recombined Milk

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

Failure to achieve optimum standardization for maximum yield efficiency is a major cause of economic loss in many cheese plants.

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.

 

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 (32-40^oC)

'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.