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Dairy Ingredients

Significance of standardizing milk for quality cheesemaking

Nana Farkye, Ph.D.

Nana Farkye, Ph.D., is professor emeritus at Cal Poly San Luis Obispo and serves as a member of the American Dairy Products Institute’s Center of Excellence. He contributes this column exclusively for Cheese Market News®.

Standardization is the adjustment of the ratio of fat to total protein (casein) in cheese milk.

Why standardize milk? Standardization is done for economic, regulatory, cheese chemistry and functionality reasons.

Milk that is used for the manufacture of cheeses is priced as Class III milk according to the provisions of the federal milk marketing orders. Class III milk price is based on skim milk price, butterfat (milkfat) price and nonfat solids price. Essentially, a cheese plant pays for milk components (i.e., fat and protein) and aims to maximize the recovery of the milk components in the cheese while meeting the regulatory standards of identity (SOI), desired quality and functional attributes for the cheese with minimal losses of major milk components in the whey.

The composition of raw milk is variable depending on breed of cow, feed, season, age and disease. The most common breeds of dairy cow in the U.S. are Holstein and Jersey, but their milk differs in protein, fat and total solids. Holstein milk has an average of 3.2% protein, 3.7% fat, 12.4% total solids and a protein-to-fat ratio of 0.86. Jersey milk has an average of 3.7% protein, 5.1% fat, 14.6% total solids and a protein-to-fat ratio of 0.73.

Protein and fat content in milk can be accurately and rapidly measured using advanced analytical techniques.

Milk contains two types of proteins — casein and whey proteins. However, there is no rapid and accurate method for measuring caseins — which are the most important milk proteins desired for cheesemaking. Therefore, the casein content of milk is estimated by multiplying the protein by a factor of 0.78 or 0.80, respectively, for milk from Holstein and Jersey cows. Therefore, the average casein content of a typical Holstein milk is 2.5% (i.e., 0.78×3.2) and that of Jersey cow milk is 2.96% (i.e., 0.80×3.7). Hence, the average casein-to-fat ratios in raw Holstein and Jersey milk are, respectively, 0.68 and 0.58 — corresponding to protein-to-fat ratios of 0.87 and 0.73, respectively.

To manufacture SOI Cheddar (minimum 50% fat-in-dry matter [FDM] and maximum 39% moisture) the ideal casein-to-fat ratio is 0.64-0.70 (equivalent to a protein-to-fat ratio of 0.80-0.90), suggesting the need to standardize raw milk for cheesemaking.

The options for standardizing cheese milk are:
1. Removal or addition of fat as cream;
2. Addition of casein as nonfat dry milk or condensed skim; or
3. Addition of fat and protein using milk processed by ultrafiltration (UF).

Options two and three are most common in cheese plants. In addition, to increase cheesemaking efficiency, the total solids in a cheese vat are increased while keeping the casein-to-fat ratio constant. It is not uncommon in modern large commercial cheese plants to use standardized milk containing 4%-5% protein and 14%-16% total solids in a cheese vat.

The efficiency and profitability of cheese manufacture involves efficient recovery of the major milk constituents (i.e., casein and fat) into cheese along with moisture and salt added during cheesemaking. In traditional cheesemaking, casein forms the structural network of the curd that retains fat and moisture, while whey (serum) proteins are lost in the whey. Earlier research shows that although good quality Cheddar can be made from milk standardized to a casein-to-fat ratio of 0.64-0.70, standardization of Cheddar cheese milk to a casein-to-fat ratio of 0.7 results in the most efficient utilization of milkfat and casein. Within the ideal limits of casein-to-fat ratio, the yield of cheese made per pound of fat in the cheese milk decreases with increasing fat content of the milk, although milkfat recoveries higher than 93% are achievable using modern equipment and cheesemaking techniques. On average, about 2.7-2.9 pounds of cheese containing 37%-38% moisture is produced per pound of milkfat in standardized milk.

Higher fat in milk results in higher FDM in the cheese. However, the optimum is 53%-54% FDM in good quality Cheddar.

The casein content of standardized milk positively affects cheese yield. Amenu and Deeth (The Australian Journal of Dairy Technology. Vol. 62, No. 3 – October 2007) reported that a reduction of the casein content in milk by 0.1% reduces Cheddar yield potential by 0.5 kilograms (kg)/100 kg milk (1.1 pounds per 220 pounds of milk), which is a significant economic loss to a cheese plant processing about 53 million gallons of milk a year. There is a relationship between casein (protein) content in standardized milk and moisture content of cheese. Literature shows that 1 pound of casein holds about 1.5 pounds of water. Because of the role of water in various biochemical reactions that occur in cheese during ripening, moisture control in cheese is important.

The amount of moisture in the nonfat substance (MNFS) of cheese ranges from 50%-58%. The higher the MNFS in cheese, the faster the rate of breakdown and more rapid deterioration of cheese after it reaches its peak flavor and body attributes. Consequently, it is preferable to target 53%-54% MNFS after one month of ripening for Cheddar that is destined to be sold as aged or ripened cheese.

Therefore, it is important to maintain a constant protein (casein)-to-fat ratio for any specific cheese regardless of the finished total solids content of the standardized cheese milk in a cheese vat. In addition to yield maximization, application of modern cheesemaking techniques to control cheese moisture, thereby controlling FDM and MNFS, optimizes cheese quality.

CMN

The views expressed by CMN’s guest columnists are their own opinions and do not necessarily reflect those of Cheese Market News®.

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