Rennet Coagulation :

🧀 Rennet Coagulation

Rennet coagulation is the enzymatic process that transforms milk from a liquid into a gel-like curd by breaking down specific milk proteins.
This step is fundamental for producing most cheeses, especially firm and aged types.

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🔬 How Rennet Coagulation Works

Rennet coagulation happens in two main phases:
1. Enzymatic Phase (Primary Phase)
2. Aggregation/Gelation Phase (Secondary Phase)

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1. Enzymatic Phase (Chymosin Action)

The key enzyme in rennet, chymosin, targets the milk protein κ-casein, which normally stabilizes casein micelles and keeps milk liquid.

What chymosin does:

• Cuts κ-casein at a specific peptide bond

• Removes the “hairy” stabilizing layer on casein micelles

• Leaves the micelles unstable and ready to bond with each other

This reaction happens relatively quickly—usually within 1–5 minutes after adding rennet to milk.

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2. Aggregation & Gelation Phase

After κ-casein is cleaved, the remaining casein micelles can now join together.

In this phase:

• Calcium bridges form between casein micelles

• Micelles cluster into a 3D network

• Milk transforms from liquid → soft gel

• Whey begins to separate

This gelation typically occurs over 10–30 minutes, depending on:

• Temperature

• Milk composition

• Rennet strength

• Calcium levels

• Acidity (pH)

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🧪 Factors Influencing Rennet Coagulation

1. Temperature

• Optimal: 30–35°C (86–95°F)

• Too cold → slow or incomplete curd

• Too hot → curd fails or becomes tough

2. pH of Milk

• Optimal pH: 6.4–6.6

• Too high (alkaline): weak curd

• Too low (acidic): too rapid coagulation or brittle curds

3. Calcium Levels

Calcium chloride (CaCl₂) is often added—especially to pasteurized or homogenized milk—to improve curd firmness.

4. Rennet Strength & Type

Liquid rennet, microbial rennet, or fermentation-produced chymosin each coagulate at different rates.

5. Milk Quality

Raw milk coagulates differently from pasteurized milk.
Goat and sheep milk coagulate faster than cow’s milk.

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🧀 Stages of Curd Formation

1. Setting (flocculation) – Milk begins to thicken

2. Soft gel formation – Curds hold together softly

3. Cutting stage – Curd is firm enough to cut cleanly

4. Syneresis – Whey expulsion occurs as curds shrink

5. Final curd texture – Determined by time, temperature, and stirring

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📌 Why Rennet Coagulation Matters

It influences:

• Cheese texture (soft, semi-hard, hard)

• Moisture content

• Aging potential

• Flavor development

• Yield efficiency

For example:

• Short coagulation → softer cheese (Brie, Camembert)

• Longer coagulation → firmer curd (Cheddar, Parmesan)

Cheese Rennet
* This extract contains a number of enzymes which are designed to help these animals digest their mother's milk, and when added to milk, rennet will cause the milk to coagulate, forming the curds and whey which are so essential in the cheesemaking process.
* Junket is a dessert which is made with sweetened, flavored milk, mixed with rennet to coagulate it. The coagulation causes the junket to set into a soft pudding, which is typically served chilled, often topped with fruit or spices.
Cheese Rennet VIDEO: