Lactic acid bacteria (LAB) work to help transform milk into cheese, creating unique flavors and textures. They ferment sugars, mainly lactose, to produce lactic acid. Earliest evidence of cheese making is c. 5500 BCE. Here's a quick look at LAB in cheese production.
Overall, cheese is very easy to make. Lactic acid bacteria already present in milk do the job themselves at room temperature, converting milk to curds (solids) and whey (liquid). Drain off the whey, salt the curd as desired and enjoy.
Lactic acid bacteria are a diverse group of gram-positive bacteria. Common genera of LAB include Lactococcus, Lactobacillus, Streptococcus, and Leuconostoc. These microorganisms are are also found in creation of other fermented products such as pickles, yogurt and salami.
In cheese production, LAB have multiple functions, including:
Fermentation: Fermentation converts the natural sugars in milk into lactic acid. This conversion is essential, as it not only helps the milk to coagulate but also contributes significantly to the cheese's flavor profile. LAB convert lactose, the sugar found in milk, into lactic acid. This process lowers the pH of the milk for the coagulation of milk proteins.
Coagulation: As lactic acid accumulates, the milk proteins, casein begin to coagulate, or clump together. Coagulation separates the solid curds from the liquid whey.
Flavor Development: The metabolic activities of LAB during fermentation contribute to the flavor and aroma of the final cheese product. They produce various byproducts, including diacetyl and acetaldehyde, to impart unique tastes and smells.
Texture Formation: LAB contribute to the texture of cheese through the breakdown of proteins and fats during fermentation.
Much experimentation goes into the perfect cheese. Strains of bacteria and environmental influences affect the final product. Artisans and cheese engineers experiment with a wide number of factors including temperatures, humidity, age, milk source and fermentation type.
Making Cheese From LAB
1. Milk Selection and Preparation
The milk can come from various animals such as cows, goats, sheep or buffalo. It's pasteurized to eliminate harmful pathogens while preserving beneficial microorganisms integral to fermentation.
The most common method of pasteurization is High Temperature Short Time (HTST) pasteurization, using metal plates and hot water to raise milk temperatures to at least 72°C (161°F) for not less than 15 seconds. This is followed by rapid cooling.
While thermophilic LAB strains can tolerate temperatures up to 65°C (149°F), heat stress above 50°C (122°F) is harmful to most LAB. The heat kills any bacteria present, and rapid cooling prevents microscopic organisms from colonizing as in slow cooling.
2. Inoculation with Starter Cultures
Once the milk is ready, specific strains of lactic acid bacteria are introduced as starter cultures. These cultures can be either mesophilic (existing in moderate temperatures) or thermophilic (high temperatures), depending on the type of cheese being made.
Mesophilic
This cheese culture is optimal for use in moderate temperatures, up to 32°C (90°F). It's used in production of hard cheeses like Monterey, cheddar, gouda, Havarti and edam. Mesophilic is also the more prevalent of the two cultures, used for cheese sensitive to high heat.
Thermophilic
This cheese culture is most active at warmer temperatures ranging from 20°- 52°C (68 - 125°F) as it consists of heat-loving bacteria. It's used in production of cheese such as mozzarella, provolone, Swiss, parmesan and Romano.
Starter cultures are concentrated amounts of specific LAB strains. Once the cultures are mixed into the milk, the LAB multiply rapidly, encouraged by the warmth and a rich supply of lactose.
3. Coagulation
As they consume lactose, LAB produce lactic acid, significantly lowering the milk's pH to more acidic. This shift in pH initiates coagulation. During curdling, the proteins in milk start to cluster, forming curds while separating from the liquid whey.
Success of this step is crucial; improper curdling can lead to poor-quality cheese, while optimal conditions yield a desirable product. In many cheese recipes rennet (an enzyme) is added to accelerate this process.
The collaboration of rennet and lactic acid bacteria turns milk into a thick gel or curd. After allowing the curds to rest, cheese makers cut the curds to drain whey effectively. The size of cuts can vary; smaller cuts result in drier cheeses.
Larger cuts retain moisture, creating softer varieties. For example, when making mozzarella, curds may be cut into larger pieces to keep the moisture content high.
4. Draining the Whey
The cut curds are then gently heated and stirred to encourage further whey expulsion. The whey is drained away, leaving behind the solid curds. Depending on the type of cheese, this step can vary significantly. Straining through a clean cloth is a common method.
Once whey has been drained, the curds are often gently heated and stirred. This practice encourages the release of additional whey until achieving the ideal consistency. Sweet whey is a byproduct from manufacture of rennet types of hard cheese, like cheddar or Swiss.
Acid whey is also referred to as sour whey. It's a byproduct in the making of acidic dairy products like strained yogurt.
5. Salting and Flavor Development
After draining the whey, the curds may be salted. This step serves several purposes: it enhances flavor, acts as a preservative, and helps regulate moisture content. The salt can also influence activity of the lactic acid bacteria, contributing to flavor and texture of the cheese.
Salting is a critical final step in cheese-making, providing flavor enhancement, moisture control, and preservation. Proper salting is essential, as it directly influences the growth of bacteria and the overall maturation process.
Salt acidifies the mix and repels pathogenic bacteria. Beneficial Lactobacillus acidophilus and Lactobacillus delbrueckii can survive at 4 and 6% salt (NaCl) levels. Their isolates can ferment sugars such as lactose xylose, glucose, sucrose and fructose.
6. Pressing
Following this, the curds are pressed into molds, allowing them to take specific shapes and further expel whey. The pressure applied during this phase influences the cheese’s final texture and firmness.
Soft cheeses like feta require minimal pressing. Harder cheeses such as gouda may be pressed for several hours to create a denser body.
7. Aging (Maturation)
Some cheeses are consumed fresh, while others undergo a maturation process, during which they develop more complex flavors and textures. During aging, the LAB continue to work on the curds, breaking down proteins and fats to enhance overall taste and aroma of the cheese.
The specific conditions of aging, such as temperature and humidity, play a crucial role in determining the final characteristics of the cheese. Aging can last from a few weeks for fresh cheeses like queso blanco to several years for aged varieties like Parmigiano-Reggiano.
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