Who cut the cheese: acidic pH chemistry?
One of the most prevalent milk products that has inserted itself into many diets and industries is the humble cheese. Whether you are looking for a soft spreadable cheese, like cream cheese or brie, or a sharp cheese like cheddar to accent a recipe that you find delectable, the origin of the process is the same, with various animal milks as starting materials. To make cheese, bacteria digest sugars in milk and produce lactic acid. The additional lactic acid lowers the pH and hinders the growth of harmful organisms.
The creation of the lactic acid in the cheesemaking process is done by one of two types of bacteria, mesophilic and thermophilic bacteria. Mesophilic bacteria grow best in moderate temperatures, typically between 20 and 45°C (68 and 113°F). They are used to make mellow cheeses such as cheddar, gouda, and colby. Thermophilic bacteria thrive between45 and 122 °C (113 and 252°F) and are used to make sharper cheeses such as Gruyère, Parmesan, and Romano.(1) The higher the lactic acid content in the milk, the lower the overall pH of the milk in the curds.
Many lactose-intolerant people can eat aged cheese without discomfort. In the cheesemaking process, the bacterial cultures ferment milk’s lactose to produce lactic acid. The longer a cheese ages, the less lactose is left over because it’s been used by the bacteria. By the time an aged cheddar or Parmesan is ready to eat, hardly any lactose remains in the cheese.(1)
In milk there are proteins that are utilized in the cheesemaking process called casein proteins. These proteins form micelle structures with in the milk. Micelles are bubbles of charged surfaces with the negative surface being on the exterior of the molecule to repel the water in milk with the positive end located at the center of the molecule/protein. In order for cheese to form this casein protein must be able to stick together. The micelles begin sticking together at around pH 5.3, with full coagulation after 24 hours, at pH 4.6.1 The rates of coagulation vary for the type of cheese that you are targeting to make. The softer cheeses, like cream cheese, require slow coagulation, whereas harder cheeses like cheddar require a faster rate, brought about by introducing a catalyst called rennet. The rennet will allow the proteins to form long bonded chains and to polymerize within themselves, holding onto the fat molecules to transform into delicious cheese.
To create the ideal environment for rennet enzymes, Gouda and cheddar should be coagulated at pH6.55, while optimal coagulation for mozzarella and Brie cheeses are at pH 6.45.(1) Once this is accomplished, the curds of the cheese, from the casein proteins are shoved into a mold or container that would be used to either store or age the cheese in question. The different taste and texture are accomplished through different rates of acidification, along with adding different culture organisms.
The chemistry seen in the creation of cheese is pH chemistry, using bacteria to acidify milk to bind the proteins into curds. The pH scale measures the concentration of hydrogen ions (H+) in a solution. The typical range for the scale is from 0 to14 on a logarithmic scale. An acidic solution ranges from 0-6.99 on the pH scale, with a neutral solution at 7. Basic solutions would range from 7.01-14 on the pH scale. Measurements would generally be done with pH paper or probes. The starting range for milk would be roughly in the 6.6-6.7 pH range.
Looking back on the batch process of cheesemaking:
· The higher the lactic acid content in the milk, the lower the overall pH of the milk in the curds.
· two types of bacteria, mesophilic and thermophilic bacteria used in cheesemaking process
· In milk there are proteins that are utilized in the cheesemaking process called casein proteins
· The softer cheeses, like cream cheese, require slow coagulation, whereas harder cheeses like cheddar require a faster rate, brought about by introducing a catalyst called rennet
· An acidic solution ranges from 0-6.99 on the pH scale, with a neutral solution at 7.Basic solutions would range from 7.01-14 on the pH scale.
Check out the activity below to test your cheesemaking knowledge:
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