1. Distribution of Components During Cheese Making

Cheese yield efficiency is about optimizing the value derived from all the dairy components passing through the plant. Typically, the most value from milk components is realized by keeping them in the cheese. Table 17.1 shows a typical distribution of milk solids between cheese and whey, given the following conditions: (1) Target moisture of 40%; (2) protein:fat ratio of 0.97 selected to achieve 50% FDM (fat-in-the-dry matter);  (3) typical fat and crude protein transfer [to cheese] coefficients of 93 and 78%, respectively, as reported by van Slyke and Price, 1908.

Table 17.1: Distribution of milk components between cheese and whey during cheese making. Expected yield is about 10% of milk weight

Given these considerations, Table 17.1 usefully illustrates the typical distribution of milk solids during cheese making. In practice the mass balance of cheese making is more complicated and is becoming more complex with an increasing array of dairy ingredients. Inputs may include any of a wide variety of milk fat sources, and milk and whey protein concentrates and isolates. Outputs may include: (1) cream removed during standardization of milk; (2) whey removed at draining; (3) whey removed after draining, sometimes after salting, and during pressing; (4) whey cream; and (5) defatted whey. Accurate determination of mass balance is, therefore, complex.

If possible it’s important to measure and maximize yield efficiency. This means maximizing the return (or minimizing the loss in the case of lactose) from all milk components entering the plant. This includes obtaining maximum returns for whey non-fat-solids, whey cream and cream skimmed during standardization. Usually the highest return for all milk components is obtained by keeping them in the cheese. Accordingly, with respect to yield the cheese makers’ objectives are to:

1. Standardize milk to obtain maximum value for milk components consistent with good quality. Historically this usually meant to adjust the protein/fat ratio to maximize cost efficiency. In current practice, it may mean substituting one source of nonfat solids for a less expensive alternative.
2. Obtain highest MNFS (moisture in non-fat substance) and SM (salt as a percentage of moisture) consistent with good quality to maximize moisture and the recovery of whey solids (within permitted standards).
3. Minimize losses of fat and casein in the whey.

To achieve these objectives the cheese maker needs to understand what factors affect cheese yield and how they can be controlled. These factors can be grouped in two categories, those that can be influenced at the farm and those that can be influenced during processing.

2. Cheese Yield Factors Controlled at the Farm

Milk quality factors that may cause altered milk composition or encourage release of proteolytic or lipolytic enzymes that break down proteins and fats. These may include high somatic cell counts, psychrotrophic bacteria, spore forming bacteria, temperature damage, excessive agitation etc. These factors are discussed in Chapter 9.

Milk composition, as discussed in Chapter 9, is influenced by genetics (species, breed, and particular protein phenotypes), feed, season, animal health, stage of lactation, and other production factors. Particularly important to cheese yield are proteins and fat. In rennet coagulated cheese and cheese made by acid coagulation of warm milk, casein is the principal structure forming and water holding component. It therefore contributes much more than its own weight to the cheese. In heat-acid precipitated varieties, whey protein play a greater role along with caseins to incorporate fat and water into the protein matrix. Fat interferes with syneresis and, therefore, also contributes more than its own weight to cheese yield, but if other conditions are adjusted to maintain constant MNFS, then fat contribution to yield is dependent only on the conversion factor of fat from milk to cheese (i.e., fraction of milk fat recovered in the cheese).

3. Cheese Yield Factors Controlled During Processing

Cheese moisture. A 1% increase in Cheddar cheese moisture causes about 1.8% increase in cheese yield, partly because the higher moisture is obtained by retaining more whey in the cheese which results in retention of more whey solids.  For example, suppose a cheese yield value of 90 Kg cheese / 1000 Kg milk with a moisture 35%. Everything else being equal, if the cheese maker increased the moisture to 36% the cheese yield would increase  by 1.7 Kg for a total of  91.7 Kg cheese / 1000 Kg milk.

Cheese salt. An extra 0.1% salt means an extra 0.14% yield of Cheddar cheese if the moisture content is increased accordingly.

Increasing time and temperature of milk pasteurization increases cheese moisture retention and the recovery of whey proteins and soluble solids. This strategy is limited because excess pasteurization hinders renneting of milk. The safe amount of denaturation of whey proteins  depends on casein level in the milk, extent of acid development, and the type of cheese.

Process control parameters

• • Careless cutting results in increased fines and loss of both fat and protein in the whey.
  • Heating too fast at early stages of cooking may cause brittle curd with more tendency to break up and release fat and protein into the whey.
  • Salting too soon after milling of Cheddar allows rapid salt uptake, which in turn causes rapid syneresis and increased solubility of casein. Yield is, therefore, reduced by losses of protein, fat and soluble solids.
  • High temperatures during pressing cause loss of fat.
  • Proteolytic cultures or coagulating enzymes cause protein losses before and after cutting.
  • Washing removes soluble solids.
  • Working, as in Mozzarella, removes fat and soluble solids. Loss of soluble solids is minimized by equilibration of the wash water with the cheese moisture.