Fermentation is a natural process driven by microorganisms that transforms organic substances, leading to desirable changes in various foods and beverages. A common question arises regarding this process: is the fermentation of cheese considered a chemical change?
Understanding Chemical and Physical Transformations
Changes in matter can be broadly categorized as either physical or chemical, each involving different alterations to a substance.
A physical change occurs when a substance alters its form or appearance, but its fundamental chemical identity remains unchanged. For instance, melting an ice cube into water or boiling water into steam are physical changes because the substance is still water, just in a different state.
A chemical change, conversely, involves a transformation where new substances with different properties are formed from the original materials. This process, often referred to as a chemical reaction, typically involves the breaking of existing chemical bonds and the formation of new ones. Burning wood, for example, is a chemical change because the wood transforms into ash, smoke, and gases, which are entirely new substances with different chemical compositions.
The Science Behind Cheese Fermentation
The cheesemaking process relies heavily on fermentation, primarily initiated by specific microorganisms, notably lactic acid bacteria. These bacteria are introduced to milk, often as starter cultures, and their main role is to break down lactose, the sugar present in milk.
Through a series of biochemical reactions, lactose is converted into lactic acid, which causes the milk’s acidity to increase and its pH to drop significantly. This acidification is a primary step, leading to the coagulation of milk proteins, known as casein, which form the solid curds of cheese.
Beyond lactose, these microorganisms and other enzymes present in the milk or added during cheesemaking also act upon the milk’s proteins and fats. Proteolysis involves the breakdown of proteins into smaller peptides and amino acids, while lipolysis refers to the degradation of fats into fatty acids and glycerol.
The specific types of bacteria, yeasts, and molds used, along with temperature and aging conditions, dictate the distinct characteristics that occur in different cheese varieties.
How Fermentation Alters Cheese
The biochemical processes occurring during cheese fermentation directly lead to the formation of new chemical compounds, fundamentally altering the milk’s original composition.
The conversion of lactose to lactic acid is a clear example, as lactic acid is a new substance not originally present in significant quantities in milk. This increased acidity influences the cheese’s texture and also helps preserve it by inhibiting undesirable microbial growth.
Further transformations of proteins and fats yield a diverse array of new molecules, including various amino acids, fatty acids, and compounds like diacetyl. These newly formed compounds are responsible for the complex and distinct flavors, aromas, and textures characteristic of different cheeses.
For instance, diacetyl contributes a buttery flavor to cheeses like Gouda, while propionic acid and carbon dioxide create the nutty flavor and characteristic holes in Swiss-type cheeses. Because these transformations result in the creation of new substances with distinct chemical properties, the fermentation of cheese is indeed a chemical change.