What is Rennet and Why is it Used?
Rennet is a complex of enzymes used in cheesemaking to curdle, or coagulate, milk, separating it into solid curds and liquid whey. The primary enzyme responsible for this coagulation is chymosin. Without a coagulating agent like rennet, making many types of cheese would be impossible. While traditionally sourced from the stomach lining of young mammals like calves, lambs, and goats, modern cheesemaking utilizes a variety of rennet types to suit different needs and dietary restrictions.
Types of Rennet
- Animal Rennet: Extracted from the fourth stomach of young, milk-fed ruminant animals. This is the most traditional form and is still required for certain cheeses protected by EU law.
- Microbial Rennet: Produced by fermenting specific microorganisms, such as fungi (e.g., Rhizomucor miehei). This is a common vegetarian alternative used in many mass-produced cheeses.
- Fermentation-Produced Chymosin (FPC): Created through genetic engineering, where a gene for chymosin is inserted into a microorganism to produce an identical enzyme. It is widely used in the industry and considered vegetarian.
- Vegetable Rennet: Derived from certain plants with milk-coagulating properties, such as artichoke thistles, nettles, or figs. This is less common in commercial production due to potential bitter flavors but is used for some specialty cheeses.
Cheeses Traditionally Made with Animal Rennet
Many of the world's most famous and aged cheeses are traditionally made with animal rennet, and for some, the use of animal rennet is a legal requirement for their protected name.
- Parmigiano-Reggiano: The authentic, legally protected Italian cheese must be made with animal rennet. Domestic U.S. versions labeled simply as 'Parmesan' are often made with vegetarian alternatives, but it is important to check the label.
- Grana Padano: Similar to Parmigiano-Reggiano, this Italian cheese also requires animal rennet for its official designation.
- Gruyère: The traditional Swiss Gruyère is made with animal rennet, though vegetarian versions may exist in the broader market.
- Pecorino Romano: This hard, salty Italian cheese is typically made with lamb rennet.
- Manchego: Authentic Spanish Manchego cheese is made with animal rennet.
- Gorgonzola: Some traditional varieties of this Italian blue cheese use animal rennet.
- Emmenthaler: Traditional Swiss Emmenthaler also uses animal rennet.
Cheeses Often Made Without Animal Rennet
While many hard cheeses are traditionally made with animal rennet, soft and fresh cheeses often use acid coagulation or microbial rennet. These include:
- Ricotta: This cheese is typically made from the whey leftover from other cheesemaking and is coagulated with heat and acid, not rennet.
- Cottage Cheese: Another acid-set cheese that doesn't rely on rennet.
- Cream Cheese: The coagulation for cream cheese is primarily done with acid.
- Mozzarella: While traditional mozzarella can be made with animal rennet, many widely available mozzarella products use microbial or vegetable rennet. Always check the label to be sure.
- Fresh Goat Cheese: Many soft, fresh goat cheeses are made with acid coagulation rather than rennet.
How to Check if a Cheese Contains Animal Rennet
Determining the source of rennet can be difficult, as many cheese labels simply list "enzymes". However, there are a few clues to look for:
- Check the Label: A label that explicitly states "microbial rennet," "vegetarian enzymes," or "vegetable rennet" is a clear indicator.
- Look for a Kosher Symbol: To be certified Kosher, a cheese must not mix milk with any meat products, so it will always be made with a non-animal rennet source.
- Be Aware of Protected Names: If a cheese is labeled with a protected name like "Parmigiano-Reggiano" and is imported, it must contain animal rennet. Domestic versions labeled differently may not.
- Contact the Manufacturer: For smaller or specialty brands, calling the company directly is often the most reliable way to get an answer.
- Look for Reputable Vegetarian Brands: Some brands, like Tillamook and Cabot, are known for using microbial or vegetarian rennet in their cheeses.
Comparison of Rennet Sources in Common Cheeses
| Cheese Type | Traditional Rennet Source | Common Alternative Source | Best Identification Method |
|---|---|---|---|
| Parmigiano-Reggiano | Animal (Calf) | Not applicable (Protected Name) | Look for protected name designation |
| Domestic Parmesan | Varies | Microbial or FPC | Check the label for "vegetable enzymes" |
| Gruyère | Animal | Microbial | Check for labels indicating vegetarian |
| Cheddar (Aged) | Often Animal | Microbial/FPC (most mass-produced) | Check the label or manufacturer |
| Mozzarella | Can be Animal | Microbial/FPC (most mass-produced) | Check the label; many are vegetarian |
| Ricotta | Not Applicable | Acid Coagulation | No rennet is typically used |
| Cream Cheese | Not Applicable | Acid Coagulation | No rennet is typically used |
Conclusion: Making Informed Cheese Choices
For vegetarians and those with specific dietary needs, knowing what cheese has rennet in it is essential. While traditional hard cheeses often contain animal rennet, the rise of vegetarian-friendly microbial and FPC alternatives means there are plenty of options available. The key is to be a savvy consumer by understanding the different types of rennet, recognizing the significance of protected cheese names, and diligently reading product labels for specific information. This allows you to make informed decisions that align with your dietary principles without sacrificing the joy of cheese. To learn more about the science of rennet, refer to its definition on Wikipedia.
