Dairy Chemistry And Biochemistry

CHEMISTRY AND BIOCHEMISTRY OF CHEESE AND FERMENTED MILKS^381

Table 10.2 Pre-treatment of cheese milk

Standardization of fat: protein ratio

Addition of skim milk

Removal of some fat

Addition of ultrafiltration retentate

Addition of CaCI,

Adjustment of pH (e.g. by gluconic acid-6-lactone)

Removal or killing of contaminating bacteria

Thermization (e.g. 65°C x 15 s)

Pasteurization (e.g. 72°C x 15 s)

Bactofugation

Microfiltration

cheese quality. The capacity of a given plant is also increased by pre-
concentrating milk by ultrafiltration.
The pH and the concentration of calcium in milk also vary, with
consequential effects on the properties of renneted milk gels. The addition
of CaCl, to cheesemilk (0.02%) is widely practised and adjustment and
standardization of milk pH by using the acidogen, gluconic acid-d-lactone
(GDL), is recommended and commercially practised on a limited scale.
Although raw milk is still widely used for cheese manufacture, e.g.
Parmigiano-Reggiano (Italy), Emmental (Switzerland), Comte and Beaufort
(France) and many less well known varieties, both on a factory and
farmhouse scale, most Cheddar and Dutch-type cheeses are produced from
pasteurized milk (HTST; c. 72°C x 15 s). Pasteurization is used primarily to
kill pathogenic and spoilage bacteria. However, desirable indigenous bac-
teria are also killed by pasteurization and it is generally agreed that cheese
made from pasteurized milk ripens more slowly and develops a less intense
flavour than raw milk cheese, apparently because certain, as yet unidentified,
indigenous bacteria are absent. At present, some countries require that all
cheese milk should be pasteurized or the cheese aged for at least 60days
(during which time pathogenic bacteria die off). A global requirement for
pasteurization of cheesemilk has been recommended but would create
restrictions for international trade in cheese, especially for many of those
with ‘Appellation d’Origine Protegee’ status. Research is under way to
identify the important indigenous microorganisms in raw milk cheese for use
as inoculants for pasteurized milk. While recognizing that pasteurization is
very important in ensuring safe cheese, pH (below about 5.2) and water
activity (aw, which is controlled by addition of NaCl) are also critical safety
hurdles.
Milk may be thermized (c. 65°C x 15s) on receipt at the factory to
reduce bacterial load, especially psychrotrophs, which are heat labile. Since
thermization does not kill pathogens, thermized milk is usually fully
pasteurized before cheesemaking.