Cheese And Milk: A Freshness Face-Off

Cheese and milk are both dairy products, but they have very different shelf lives. While milk usually lasts for about a week, cheese can last for several months. This is because cheese is made from milk that has been processed to remove moisture and add salt, creating an environment that inhibits bacterial growth. The type of cheese also determines its longevity, with harder, aged cheeses like Parmesan and Asiago lasting longer than softer varieties like Brie and Camembert. Additionally, the way cheese is stored can impact its shelf life, with proper refrigeration and breathable wrapping methods helping to extend its freshness. In the case of milk, organic milk tends to have a longer shelf life due to ultrahigh-temperature (UHT) processing, which kills all bacteria and allows the milk to be stored at room temperature for up to six months. However, UHT-treated milk has a sweeter flavour due to caramelization, and it is not suitable for making cheese.

Why does cheese last longer?

Cheese is a product of highly controlled action by bacteria that produce acids that coagulate the casein in milk. The type of bacteria, the temperature, the amount of time they are allowed to act, and the amount of water drained from the curdling milk all influence the end result in terms of texture, taste, and flavour.

Cheese is not a sterile product, even when made with pasteurized milk. Bacteria remain inside the cheese, and bacteria, moulds, and yeast land on its surface during processing and shelf time. However, the action of these bacteria can be slowed by cold and dry conditions, which is why harder cheeses with less moisture last longer than softer cheeses.

Harder, aged cheeses will last the longest in the fridge, with most able to last four to six months if stored correctly. All cheese will lose moisture and change over time, but harder cheeses have less internal moisture, so they are the least affected. Harder cheeses are also less susceptible to mould, and if mould does appear, it can be cut off without ruining the cheese.

Semi-hard and semi-soft cheeses have a shorter shelf life due to their higher moisture content. They typically last two to four weeks after their expiration date, and any mould that appears cannot be cut off and should be discarded.

Soft cheeses are the most susceptible to spoilage and should be consumed within one to two weeks of their expiration date. They have a high moisture content, which makes them prone to spoilage. Any sign of mould means the entire product should be discarded.

The effect of moisture on milk and cheese

Milk is made up of 90% water, whereas cheese consists of the proteins and fats derived from milk. The moisture content of cheese is a key factor in determining its yield and profitability. Cheesemakers can control the moisture content of their product by adjusting various parameters during the cheesemaking process, such as curd particle size, cooking temperature, and salting.

The moisture content of cheese also affects its texture, rheology, and microstructure. Increasing the moisture content leads to increased meltability and decreased hardness. However, there is a maximum level of moisture that the cheese matrix can retain, beyond which pockets of "free" water form within the cheese.

Additionally, the moisture content of feed consumed by dairy cows impacts their nutrient intake and milk production. A diet with more than 50% moisture can lead to reduced dry matter intake, as the essential nutrients become less concentrated. This, in turn, affects the milk production of the cows.

The role of bacteria in milk and cheese

Milk is a complex fluid that contains a diverse community of bacteria, viruses, fungi, and other microorganisms. This microbial community, known as the milk microbiota, plays a crucial role in the health and development of both the mother and the infant. The milk microbiota is influenced by various factors, including the mother's health, diet, geography, and environmental factors.

The process of cheese-making involves the transformation of milk into a solid or semi-solid product through the action of bacteria, salt, rennet, and other coagulants. This process is dependent on the growth and activity of specific bacteria, particularly lactic acid bacteria, which play a crucial role in converting milk sugar (lactose) into lactic acid. This lowers the pH of the milk, creating an environment inhospitable to spoilage organisms and contributing to the unique flavour and texture of cheese.

The specific types of bacteria present in milk and cheese can vary depending on several factors. In traditional cheese-making, for example, the cheese may be inoculated using whey or other products from previous batches, resulting in a diverse range of microbes. On the other hand, modern cheese-making often involves the use of preselected cultures with only a few types of bacteria.

The bacteria in milk and cheese can have a significant impact on the health of both the mother and the infant. For instance, the presence of beneficial bacteria, such as bifidobacteria and lactobacilli, in human milk can contribute to the development of a healthy gut microbiota in newborns. Additionally, the milk microbiota has been linked to the mother's health, particularly in cases of mastitis or other infections.

In conclusion, the role of bacteria in milk and cheese is multifaceted and complex. Bacteria are essential for the cheese-making process, contributing to flavour and texture, while also playing a vital role in the health and development of both the mother and the infant. The specific types and functions of bacteria can vary depending on the cheese-making process and environmental factors, highlighting the dynamic nature of the milk and cheese microbiota.

The impact of temperature on milk and cheese preservation

For milk, refrigeration temperatures between 4°C and 10°C can maintain its quality for up to 10 days. However, lower temperatures, such as refrigeration at 4°C, can promote the growth of psychrotrophic microorganisms, which can negatively impact the yield and quality of dairy products. These bacteria produce lipases and heat-resistant proteases, altering flavour and aroma and causing a weak curd during cheese-making.

Freezing milk can also have adverse effects, as it changes the structure of milk constituents. It increases the lipid oxidation rate, alters soluble and colloidal mineral fractions, and destabilises proteins. However, freezing can be a viable option for short-term preservation, as milk frozen for up to 30 days can still be used to produce cheese with minimal changes in texture and physicochemical characteristics.

Regarding cheese preservation, temperature plays a crucial role in determining its shelf life. In general, harder cheeses with less moisture last longer than softer, more mature cheeses. Proper storage of cheese at or below 40°F (4.4°C) can extend its shelf life significantly. For example, harder cheeses like Parmesan, Asiago, and Romano can last for four to six months in the refrigerator when stored correctly. On the other hand, soft cheeses like cottage cheese, cream cheese, and Brie are more perishable and should be consumed within one to two weeks of their expiration date, even when stored properly.

Additionally, the temperature at which milk is cooled before cheese-making can impact the final product. For instance, in the production of Parmigiano Reggiano, a lower cooling temperature of 9°C can better control microbial growth and improve the hygienic characteristics of the milk. However, it can also lead to slightly higher losses of macroconstituents in the whey and negatively affect coagulation properties.

In summary, temperature plays a critical role in milk and cheese preservation. Proper refrigeration and freezing temperatures can extend the shelf life of these products, but the specific temperature requirements and effects differ between milk and various types of cheese.

The difference between organic and regular milk's shelf life

Cheese can last longer than milk, depending on the type of cheese and milk in question. For example, hard cheeses like Parmesan and Asiago can last for four to six months in the fridge, while soft cheeses like cottage cheese and cream cheese will only last a few weeks. As for milk, organic milk typically has a longer shelf life than regular milk, lasting up to two months, whereas regular milk usually only lasts about one to two weeks.

The main difference between organic and regular milk's shelf life is the preservation process used. Organic milk often undergoes a process called ultra-high-temperature (UHT) processing or treatment, in which the milk is heated to 280°F (138°C) for two to four seconds, killing any bacteria in it. This gives organic milk a longer shelf life of up to two months. On the other hand, regular milk typically undergoes pasteurization, which only kills enough bacteria to prevent diseases, and does not affect all bacteria. This results in a shorter shelf life of about one to two weeks.

The reason for the different preservation processes is related to the distribution of organic and regular milk products. Organic products often have to travel farther to reach store shelves since they are not produced as widely as regular milk. Therefore, the milk needs to stay fresh for longer, hence the use of UHT processing.

It is worth noting that UHT-treated milk does have a different taste and texture due to the caramelization of sugars and the destruction of some milk proteins. This may be off-putting to some consumers, particularly those used to the taste of regular milk. Additionally, UHT milk cannot be used for making cheese as it affects the milk proteins.

In summary, the difference between organic and regular milk's shelf life comes down to the preservation process used, with organic milk undergoing UHT processing, resulting in a longer shelf life, a sweeter taste, and a creamier texture.

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