High pressures increase cheese yield.

High-pressure processing of the milk used to make cheese causes whey proteins to denature and form disulfide bonds with casein micelles. Incorporating whey proteins into the casein matrix could increase the dry matter and water content of the final product. This would increase the cheese wet yield by at least 8%.

The goal of researchers at Washington State University was to determine the extent of the wet yield increase caused by high-pressure processing, and to see how it compares with raw and high-temperature/short-time (HTST) pasteurized milk. Cheddar cheeses were made with raw HTST milk (72 C, 15 sec), 483 MPa (22 C, 5 min), 676 MPa (22 C, 5 min) and 676 MPa (60 C, 5 min). The milk was standardized to a butterfat-to-protein ratio of 1.2, and cheeses were made following a standard procedure.

Researchers repeated the cheddaring step until a final titratable acidity between 0.53% and 0.56% was reached. Cheeses were vacuum-packed and stored at 5 C. The cheeses exhibited variable cutting times, depending on the treatment applied. Coagulums obtained from raw and HTST pasteurized milk were cut after 20 minutes of enzyme addition.

High-pressure treatment decreased the cutting time to 18 min and 16 min for the 483 MPa and 676 MPa treatments, respectively. Cheeses made from raw and HTST pasteurized milk exhibited the lowest yields at 10.6% and 10.5%, respectively.

Milk treated at the highest pressure and at room temperature exhibited the highest yield: 11.4%. The cheese that was treated at 483 MPa exhibited a 10.8% wet yield. The high-pressure treatment of milk at 60 C prevented curd granules from fusing together. Cheese could not be made under these conditions.

Increases in cheese yield caused by solid retention are desirable as long as the texture and other sensory attributes of the product are not compromised. Using high pressures could achieve an 8% yield increase, compared with cheeses made with raw or HTST pasteurized milk.

Investigators conclude that cheese yield from ultra-high-pressure-treated milk increases as a result of increased moisture and the incorporation of additional dry matter. We do not know if the dry matter increase results from alterations in the casein micelles or whey proteins, although we know the structure of both are altered during ultra-high-pressure processing.

This application of ultra-high pressure is available to the dairy industry with considerable capital expenditures. The quality of the cheeses produced is not yet well documented, so the next steps may be to continue experimentation with ultra-high-pressure processing of milk and examine the processes that result in the greatest increases in yield and acceptable quality.

Further information. Barry Swanson, Department of Food Science and Human Nutrition, Washington State University, 106K FSHN Building, P.O. Box 646376, Pullman, WA 99164; phone: [phone]; fax: [phone]; email: [e-mail].