The Traditional Source: Animal Rennet
For thousands of years, rennet was exclusively sourced from the stomachs of young, milk-fed ruminant animals. The primary enzymes, including chymosin, aid these animals in digesting their mother's milk by coagulating it.
How Animal Rennet is Produced
- Source: Historically, the inner mucosa of the fourth stomach chamber (abomasum) of young calves, lambs, or kids was used.
- Preparation: Dried and cleaned stomach linings were soaked in a brine or whey solution to extract the enzymes.
- Modern Production: Today, production may involve milling deep-frozen stomachs and activating the enzymes with acid before filtering and concentrating the solution.
Animal rennet contains a mixture of enzymes, including chymosin and pepsin, which can contribute to the specific flavor and texture profiles prized in certain artisanal and aged cheeses. Due to ethical concerns, dietary restrictions (kosher, halal), and inconsistent supply, alternatives were developed.
The Vegetarian Alternatives: Microbial and Vegetable Rennets
As cheese consumption grew and dietary preferences evolved, cheesemakers sought non-animal options. Two key alternatives emerged.
Microbial Rennet
First commercialized in the 1970s, microbial rennet is derived from the fermentation of specific fungi or bacteria, such as Rhizomucor miehei.
- Production: The selected microorganism is grown in a fermenter, and the proteolytic enzymes are extracted, concentrated, and purified.
- Characteristics: These enzymes coagulate milk effectively, making them a popular, less expensive option for many commercial cheeses. However, older versions of microbial rennet were sometimes associated with bitter flavors in long-aged cheeses due to higher non-specific proteolytic activity. Modern purification methods have largely overcome this issue.
Vegetable Rennet
Plant-based rennets have been used for centuries and are derived from various plants with milk-curdling properties.
- Examples of Plant Sources: Cardoon thistle flowers, fig sap, stinging nettles, and lady's bedstraw.
- Production: Enzymes are extracted by soaking or macerating parts of the plant.
- Challenges: Vegetable rennet can be inconsistent in strength and may impart a bitter flavor to the cheese, especially in cow's milk. For this reason, its use is limited to specific traditional cheeses, like some Portuguese and Spanish sheep cheeses.
The Modern Standard: Fermentation-Produced Chymosin (FPC)
This is the most dominant type of rennet in the global cheese industry today, accounting for over 90% of the market share.
How FPC is Made
Fermentation-produced chymosin is a product of modern biotechnology.
- Genetic Engineering: The gene for calf chymosin is inserted into a microorganism, such as yeast (Kluyveromyces lactis) or a fungus (Aspergillus niger).
- Fermentation: The modified microorganism is grown in a fermentation vat, where it produces large quantities of chymosin.
- Purification: The chymosin enzyme is harvested and purified, with the genetically modified microorganism removed completely from the final product.
Benefits of FPC
- Consistency: FPC is a pure enzyme, resulting in consistent coagulation, which minimizes defects.
- Efficiency: It is produced in large, economical quantities in a factory setting.
- Dietary Friendly: Since no animal products are used in its production, FPC is suitable for vegetarians, kosher, and halal diets.
Choosing the Right Rennet: A Comparison
| Feature | Animal Rennet | Microbial Rennet | Vegetable Rennet | Fermentation-Produced Chymosin (FPC) |
|---|---|---|---|---|
| Source | Stomach of young ruminants (calf, lamb) | Specific fungi or bacteria | Plant sources (thistle, fig sap) | Genetically engineered microbes |
| Availability | Limited supply, byproduct of meat industry | Readily available, economical | Niche product, can be inconsistent | Widely available, dominant market share |
| Dietary | Not vegetarian, kosher, or halal compliant | Vegetarian, typically kosher | Vegetarian | Vegetarian, kosher, and halal certified |
| Flavor Impact | Complex, traditional flavor, good for aged cheese | Neutral, modern versions have minimized bitterness | Can impart a bitter flavor | Clean, reliable flavor profile, no bitterness |
| Use Case | Traditional and artisanal cheeses, especially aged varieties | Many commercial, short-aged, and fresh cheeses | Artisanal and traditional cheeses, regional specialties | Most industrial and commercial cheese production globally |
Conclusion
The question of "what is rennet made from" reveals a complex evolution in cheesemaking. While animal rennet represents centuries of tradition, modern advancements have created more consistent, ethical, and scalable alternatives. Fermentation-produced chymosin (FPC) has become the dominant industry standard, providing reliability and suiting a wider range of dietary needs. Meanwhile, microbial and vegetable rennets serve specific market niches and traditional applications. The choice of rennet depends on the desired cheese characteristics, production scale, and ethical or dietary considerations. Regardless of the source, rennet's role in coagulating milk remains a cornerstone of cheese production.
For more detailed information on fermentation-produced chymosin, you can consult this resource from Wikipedia: Chymosin.
