What is Rennet and Why is it Used?
Rennet is a complex set of enzymes, with the primary one being chymosin, that is crucial for cheesemaking. Its purpose is to act as a coagulant, causing the milk proteins (casein) to clump together and form solid curds. This process separates the curds from the liquid whey and is a fundamental step for producing most cheeses, particularly harder types and low-moisture mozzarella used on pizza.
Historically, rennet was harvested from the stomach lining of young, unweaned calves, lambs, or goats. This traditional animal-derived rennet makes the resulting cheese unsuitable for vegetarians. For centuries, this was the standard method, but an increased global demand for cheese, particularly mozzarella for the booming pizza industry, led to a worldwide shortage of animal rennet in the mid-1970s.
The Shift from Animal Rennet to Vegetarian Alternatives
In response to the demand and the ethical considerations of animal-derived products, scientists in the 1980s developed reliable, cost-effective vegetarian alternatives. This technological shift revolutionized the industry and made it possible to produce vegetarian-friendly cheeses on a large scale. Today, most commercially produced mozzarella, including the shredded or low-moisture varieties popular for pizza, is made with these alternatives.
The Rise of Microbial and FPC
There are two main types of vegetarian-friendly rennet that have replaced traditional animal rennet:
- Microbial Rennet: Produced by fermenting certain fungi or molds, such as Rhizomucor miehei. These enzymes effectively coagulate milk and are widely used in commercial cheesemaking today.
- Fermentation-Produced Chymosin (FPC): Created using genetic engineering, FPC is a purer form of chymosin. Scientists transfer the gene for calf chymosin into a microbial host, like yeast, which then produces the enzyme through fermentation. FPC is highly similar to animal rennet in its function and is now responsible for up to 90% of the rennet market share globally.
Can any Mozzarella be made without Rennet?
While less common for the mozzarella used on pizza, some fresh, soft cheeses are made using an acid coagulant, such as citric acid or vinegar, instead of rennet. This process yields a softer curd and is typically used for fresh mozzarella sold in logs or brine. This method is, by its nature, vegetarian.
Decoding the Label: How to Know if Your Mozzarella is Vegetarian
For consumers, the most effective way to determine if your pizza mozzarella is suitable for a vegetarian diet is to read the ingredient label carefully. Manufacturers are not legally required to specify the type of rennet, but most brands catering to a vegetarian market will clearly label their products.
- Look for clear declarations: Phrases such as “microbial enzymes,” “vegetable rennet,” or “non-animal rennet” indicate a vegetarian-friendly product. Some brands may also include a “vegetarian safe” symbol or certification.
- Beware of vague terms: If the label only lists “enzymes,” there is ambiguity. In this case, you can contact the manufacturer or assume that, given modern production methods, it is likely microbial. However, for strict adherence to a vegetarian diet, clearer labeling is preferred.
- Identify traditional products: Artisanal, imported, or traditional mozzarella may still use animal rennet. This is especially true for Protected Designation of Origin (PDO) cheeses where the traditional recipe is legally enforced.
Is There a Difference Between Rennet Types for Pizza?
For pizza mozzarella, which is a mild, unaged cheese, the average person is highly unlikely to taste a difference between a product made with animal rennet versus a microbial or FPC alternative. The performance, including the desired melt and stretch characteristics, is largely comparable due to the advances in microbial and FPC enzyme technology. Bitterness, a potential side effect of older microbial rennet formulas, is primarily a concern for long-aged cheeses, which pizza mozzarella is not. Therefore, the choice between rennet types for pizza cheese is primarily an ethical or dietary decision, not a culinary one.
Comparison of Rennet Types in Mozzarella
| Feature | Animal Rennet | Microbial Rennet/FPC | Acid Coagulation |
|---|---|---|---|
| Source | Stomach of young ruminants (calves, etc.) | Fungi, molds, or engineered microbes | Lactic acid cultures, citric acid, or vinegar |
| Vegetarian? | No | Yes | Yes |
| Common Use | Traditional, often artisanal, cheeses | Most commercial mozzarella for pizza | Fresh mozzarella balls, ricotta |
| Flavor Impact | Clean, traditional cheese flavor | Neutral for fresh/mild cheese | Tangy, as with fresh cheeses |
| Aging Suitability | Excellent for long aging | Possible bitterness in long-aged cheeses | Not suitable for aging |
Conclusion: Making Informed Dietary Choices
Today's consumer has more choices than ever when it comes to cheese, and understanding the source of rennet is a key part of making informed dietary decisions, especially for vegetarians. While traditional mozzarella often contained animal-derived rennet, the vast majority of pizza mozzarella on the market today is made with vegetarian-friendly microbial or fermentation-produced enzymes. The best practice is to always check the ingredient label for phrases like “microbial enzymes” or a specific vegetarian certification. For those seeking fresh mozzarella, or an even simpler approach, acid-coagulated varieties offer a completely rennet-free option. Ultimately, finding a delicious and ethically sound mozzarella for your pizza is easier than ever with a little knowledge.
