Rennet is a complex set of enzymes central to many cheeses. It coagulates milk to form curds. The primary enzyme in rennet is chymosin (rennin), responsible for curdling milk to separate solids from whey.
About Rennet
Rennet comes from the stomach linings of ruminant animals, especially calves. When added to milk, rennet causes proteins like casein to curdle, separating liquid whey from solid curds.
In nature, rennet serves a biological function for young mammals. It helps them digest raw milk from their mothers and absorb nutrients efficiently.
In cheese making, rennet mimics the natural process, as cheesemakers transform liquid to solids. The curds will eventually be pressed and aged to yield various cheese varieties.
Rennet influences both texture and flavor of the cheese. For example, mozzarella made with rennet is chewy, while a soft cheese like ricotta has a creamy consistency.
Historical Use of Rennet
Rennet has a long history, dating back thousands of years. Records show cheese making starts c. 8000 BCE, integrating rennet from the start. Other records show it begins c. 5000 BCE with Egyptians and Sumerians.
Ancient cultures store milk in animal stomachs, which preserve and convert it into a nutritious product. For Neolithic humans, many of whom have not yet developed the lactose gene, cheese is perfect nourishment.
About 90% of lactose is removed during the cheese making process. Archaeological findings show cheese is a common food in ancient civilizations.
Enzymes in Rennet and Their Functions
Rennet primarily contains the enzyme chymosin, but it also includes other proteolytic enzymes such as pepsin, which further break down proteins during the coagulation process.
Chymosin specifically targets casein proteins in milk, making them aggregate and form curds. This enzymatic action is essential for the structure and texture of the cheese, from soft to hard aged varieties.
Scholars suggest chymosin can curdle milk 70% more effectively than acid (vinegar, lemon juice) alone.
Lipase is another important enzyme. Useful for fat breakdown, lipase contributes to the flavor profile of certain cheeses, such as the distinct sharp taste of aged cheddar.
Cheese Using Rennet
Rennet is a fundamental ingredient in most traditional cheese making, and it is used in a wide variety of cheeses, including:
Cheddar
Parmigiano-Reggiano
Brie
Gorgonzola
Gouda
Havarti
Artisan cheese makers rely on rennet to craft specific textures and flavors unique to their creations. The rich, nutty flavor profile of an aged gouda is attributed to the type of rennet used.
Rennet provides consistency and a particular flavor profile to the cheese. While many artisanal cheese varieties use traditional rennet, some opt for vegetarian or microbial rennet alternatives.
Microbial-derived rennet substitutes consist of relatively purified proteases secreted by fungal species, such as Rhizomucor miehei, which affects milk in similar ways to natural rennet.
Rennet from microbial sources is usually created through fermentation, using microbes such as modified Kluyveromyces lactis or Aspergillus niger.
Are Calves Killed for Rennet?
One of the ethical concerns surrounding use of rennet relates to its source. Traditional rennet is derived from the stomachs of young unweaned calves, which raises questions about animal welfare.
While some calves are slaughtered for their stomach linings, many cattle farmers raise the animals with the intent of producing milk and veal. There is a growing movement towards cruelty-free cheese production.
More cheesemakers are seeking rennet alternatives, or sourcing from farms prioritizing ethical treatment of animals. More consumers are taking time to consider the source of food.
Natural Alternatives to Rennet
Several natural alternatives to animal-derived rennet are on the shelves. These include:
Vegetable Rennet: Derived from certain plants, such as thistle, nettle, and fig, vegetable rennet can be used to coagulate milk for cheese production. An example is use of thistle rennet in some Mediterranean cheese.
Microbial Rennet: Produced through fermentation of specific fungi or bacteria, this type of rennet is commonly used in commercial cheese production.
Acid Coagulation: Some cheeses, such as ricotta, use acid (like vinegar or lemon juice) to curdle milk, completely avoiding the need for rennet.
Genetically Engineered Rennet: Created using recombinant DNA technology, this alternative mimics the function of traditional animal rennet and is widely adopted by large-scale cheese manufacturers.
These alternatives not only address ethical concerns but also provide cheese makers with creative avenues for experimenting with unique flavors and textures.
Facts About Rennet
Ancient Preservation: The method of using rennet to coagulate milk predates recorded history and is regarded as one of humanity's earliest forms of food preservation.
Flavor Influence: The type of rennet and the source (animal, microbial, vegetable) can significantly influence the flavor and texture of the resulting cheese.
Cultural Variety: Different cultures utilize different types of rennet and cheese-making techniques, leading to diverse cheese varieties around the world.
Historical Significance: Certain exclusive cheese recipes are passed down through generations.
Flavor Depth: The rennet type used can significantly influence cheese flavor. Microbial rennet can produce cheeses with unique notes distinct from those made with animal rennet.
Vegetarian Cheese: Although traditional rennet is animal-derived, many cheeses labeled as “vegetarian” use non-animal sources of rennet to cater to a broader audience.
Global Movement: As more consumers become aware of animal welfare issues, the cheese industry is adapting by creating more ethical and sustainable cheese options.
Biotech Breakthrough: Advances in biotechnology have led to the development of rennet produced through fermentation. This method strongly reduces the environmental impact of industrial production.
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