Introduction and Classification of Cheese
Cheese is a consolidated dairy product derived from milk by coagulation of milk protein casein, separating the whey, and ripening the resulting curd with specific microorganisms and enzymes. It serves as an essential method of preserving surplus milk solids, rich in proteins, fats, calcium, and fat-soluble vitamins.
- Classification Based on Moisture Content: Soft cheeses (Cottage, Camembert, moisture > 55%), Semi-hard cheeses (Gouda, Edam, moisture 39-50%), Hard cheeses (Cheddar, Swiss, moisture 34-39%), and Very hard cheeses (Parmesan, Romano, moisture < 34%).
- Classification Based on Ripening Agent: Unripened (fresh curd products like Paneer, Mozzarella) and Ripened (bacteria-ripened or mold-ripened).
Microbiology and Starter Cultures in Cheese Making
Starter cultures are vital microbial inoculants added to milk to ferment lactose into lactic acid, lowering pH and assisting in curd formation, syneresis, and pathogen inhibition.
- Mesophilic Cultures: Optimum growth temperature between 20°C and 30°C. Includes Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris, and Leuconostoc species used for Cheddar and Gouda.
- Thermophilic Cultures: Optimum growth temperature between 42°C and 45°C. Includes Streptococcus thermophilus, Lactobacillus helveticus, and Lactobacillus delbrueckii subsp. bulgaricus used for Swiss and Italian hard cheeses.
- Secondary Flora: Propionibacterium freudenreichii subsp. shermanii for eye formation and flavor in Swiss cheese; Penicillium camemberti and Penicillium roqueforti for surface and interior mold-ripened cheeses respectively.
Biochemistry of Coagulation and Rennet Action
Coagulation is the primary step converting liquid milk into a gel matrix. It is achieved via enzymatic action (rennet) or acid precipitation.
- Rennet Coagulation: Chymosin (rennin), extracted from the abomasum of unweaned calves or produced via recombinant DNA technology, specifically cleaves the peptide bond between phenylalanine (105) and methionine (106) in kappa-casein.
- Glycomacropeptide Release: The hydrophilic C-terminal portion (kappa-casein glycomacropeptide) is cleaved off and released into the whey, destabilizing the casein micelle steric stabilization.
- Calcium-Mediated Aggregation: In the presence of divalent calcium ions (Ca2+) and temperatures around 30°C to 32°C, destabilized para-kappa-casein micelles aggregate to form a continuous three-dimensional network (curd).
Step-by-Step Cheese Manufacturing Process
The standardized industrial manufacture of hard and semi-hard cheeses like Cheddar involves sequential unit operations.
- Standardization and Pasteurization: Adjusting the Fat-to-Solids-Not-Fat (SNF) ratio and destroying pathogenic microorganisms via HTST pasteurization (72°C for 15 seconds).
- Inoculation and Ripening: Addition of starter cultures to condition the milk and develop acidity.
- Renneting and Cutting: Addition of rennet, setting the curd, and cutting into uniform cubes to facilitate whey drainage (syneresis).
- Cooking, Salting, and Hooping: Raising temperature to shrink curd particles, draining whey, dry salting or brine immersion, and pressing into molds (hoops) to expel remaining moisture.
Ripening (Curing) and Storage Technology
Ripening transforms raw, rubbery curd into a flavorful, digestible cheese with distinct textural characteristics through biochemical breakdown of proteins, fats, and residual lactose.
- Glycolysis: Fermentation of residual lactose into lactic acid, propionic acid, acetic acid, and carbon dioxide.
- Proteolysis: Breakdown of casein proteins into large peptides, small peptides, and free amino acids by residual rennet and microbial proteases/peptidases.
- Lipolysis: Hydrolysis of milk fat triglycerides into free fatty acids, aldehydes, and ketones, which contribute significantly to the characteristic aroma and flavor profiles of aged cheeses.
Comparison of Major Cheese Types and Parameters
| Parameter | Cheddar Cheese | Swiss (Emmental) Cheese | Mozzarella Cheese |
|---|---|---|---|
| Moisture Content | 34% - 39% (Hard) | 36% - 40% (Semi-hard) | 45% - 55% (Soft/Fresh) |
| Primary Starter Culture | Lactococcus lactis subsp. lactis | Streptococcus thermophilus & Lactobacillus helveticus | Streptococcus thermophilus |
| Coagulation Agent | Rennet + Acid | Rennet | Rennet + Direct Acidification |
| Unique Feature | Cheddaring process (piling and turning slabs) | Eye formation due to CO2 from Propionibacterium | Plasticizing (pasta filata) by stretching in hot water |
Memory Trick / Mnemonic
Stages of Cheese Making
S-I-R-C-S-S-P-R (Sir Cooks Salt So Carefully Since Ripening Pays)
S: Standardization, I: Inoculation, R: Renneting, C: Cutting, S: Stirring/Cooking, S: Salting, P: Pressing, R: Ripening.
⚡ High-Yield Exam Points (UP TGT / PGT Focus)
- Chymosin is the primary proteolytic enzyme found in rennet that specifically cleaves the Phe105-Met106 bond of kappa-casein.
- The process of piling and turning curd blocks during Cheddar cheese manufacture is known as 'Cheddaring'.
- Propionibacterium freudenreichii subsp. shermanii is responsible for the characteristic eyes and sweet, nutty flavor in Swiss Emmental cheese.
- Syneresis refers to the spontaneous contraction of a coagulated milk gel and the expulsion of whey.
- Moisture content in hard cheese such as Parmesan is below 34%, whereas soft cheese such as Cottage cheese exceeds 55%.
- Pasta filata is a unique stretching and kneading manufacturing technique used for Mozzarella and Provolone cheeses.
⚠️ Common Mistakes & Exam Pitfalls
- Confusing mesophilic and thermophilic starter cultures; mesophilic cultures grow best at 20-30°C (Cheddar), while thermophilic grow at 42-45°C (Swiss/Italian).
- Assuming all cheese undergoes microbial ripening; fresh unripened cheeses like Cottage and Paneer do not undergo curing.
- Believing that rennet acts directly on calcium caseinate without prior enzymatic cleavage of kappa-casein.