The Science of Cheese Production: Enzymatic Coagulation, Microbial Cultures, and Aging

Cheese making is an ancient biotechnological art and modern biochemical science that transforms perishable liquid milk into stable, nutrient-dense solid food through controlled enzymatic coagulation, lactic acid fermentation, curd synaeresis, and biochemical aging (affinage).

This guide details the physical chemistry of casein micelles, enzymatic cleavage by chymosin (rennet), lactic acid bacteria (LAB) kinetics, moisture expulsion, and proteolysis/lipolysis during ripening.

1. Quick-Reference: Stages of Cheese Production

+-----------------------------------------------------------------------------------------+
|                               CHEESE MAKING STAGES                                      |
+-----------------------------------------------------------------------------------------+
| Stage                  | Biochemical Action                | Key Reaction Invariant     |
+------------------------+-----------------------------------+----------------------------+
| 1. Acidification       | Lactic Acid Bacteria (LAB) growth | pH drops from 6.7 to 5.2   |
| 2. Coagulation         | Chymosin cleaves κ-casein peptide | Hydrophobic gel network    |
| 3. Curd Cutting & Cook | Mechanical shear + heat expels whey| Controls curd moisture %   |
| 4. Salting & Pressing  | Dehydrates surface, inhibits spoilage| Forms protective rind   |
| 5. Affinage (Aging)    | Proteolysis & lipolysis breakdown | Develops volatile aromas   |
+-----------------------------------------------------------------------------------------+

2. Enzymatic Coagulation Chemistry

Milk proteins exist primarily as casein micelles ( $lpha_{s1}, lpha_{s2}, eta$ , and $\kappa$ -casein) stabilized by a hydrophilic outer hair-like layer of $\kappa$ -casein with negative surface charge that prevents aggregation.

Rennet Reaction: The aspartic protease chymosin specifically cleaves the $ext{Phe}_{105} - ext{Met}_{106}$ peptide bond of $\kappa$ -casein, releasing the hydrophilic glycomacropeptide (GMP) into the whey.
The remaining hydrophobic para- $\kappa$ -casein micelles lose electrostatic repulsion and aggregate in the presence of calcium ions ( $ext{Ca}^{2+}$ ) into a continuous three-dimensional protein mesh trapping fat globules.