The following piece by Palak Pujara was originally published by Milwaukee Area Science Advocates.
Wisconsin is known for its cheese, and rightfully so. It’s at our sporting events and referenced on our license plates. It is fairly difficult to avoid cheese in Wisconsin. What many might not realize while enjoying their favorite food is how much science is involved in making the perfect cheese.
There is no doubt that Wisconsin loves its cheese. Just look at our nickname, The Cheeseheads, and you can safely assume that Wisconsin produces the most cheese in the US. However, Wisconsin did not start producing cheese until the mid 1800s, which is late compared to its European and Egyptian counterparts whose cheese origins go back over 4000 years. Historians are not sure who, when, nor how cheese was first discovered. The timing is only an approximation. There are references to cheese in the Greek mythology, The Odyssey, which was written at the end of the 8th century BCE. By the time the Roman Empire came to power in 117 AD, cheese was widespread across Europe and the Middle East. So while the origins of cheese are a mystery, it’s safe to say it has been a big part of society for a long time.
Historians believe that cheese was first discovered by accident. Milk was commonly stored in vessels made of hollowed out animal stomachs. When milk was stored in the stomachs of young milk-producing animals, such as cows, the milk would curdle and would be preserved. Though they did not know this at the time, this was due to rennet, which is naturally found in the fourth stomach of young calves and helps them digest their mother’s milk. The rennet contains an enzyme called chymosin. Enzymes are a specific type of protein, which make a particular reaction occur quicker than it would otherwise. All animals, including humans, contain various enzymes and bacteria throughout their digestive system to help breakdown food quickly. In the case of chymosin, milk curdles more quickly by changing the properties of its proteins. Early cheesemakers would separate these curdles from the remaining liquid, or whey, and salt them to enjoy later. In the days before refrigeration, the discovery and development of cheesemaking was very advantageous since it allowed the prolonged storage of a high-calorie, protein-rich food source.
Today, the basic cheesemaking process is not very different. Though cheesemakers have long abandoned storing milk in the stomachs of cows and there are synthetic sources of rennet available, the same basic steps are followed. The first step is still to curdle milk. This will naturally occur over time, as anyone who has forgotten about the milk in the back of the fridge knows. However, the way cheesemakers cause curds to form is a lot more scientific and controlled.
Milk itself is a fairly complicated emulsion. Emulsions are mixtures of two or more liquids that are immiscible, or do not mix together to form one continuous state. Cow’s milk is 86% water and contains fats, carbohydrates, proteins, minerals and vitamins. The carbohydrates, which are mostly lactose, and minerals are hydrophilic. This means they are water soluble and “water loving.” Whey is one of the two primary proteins found in milk and is also hydrophilic. The fat however, is hydrophobic, and is not soluble in water. It, along with casein, the other primary protein found in milk, is suspended in the water to form the emulsion. Though you cannot see the casein and fat floating in your milk, scientist can see the fat globules and casein micelles under a microscope.
The fat is found in little globules in the same way oil droplets are found in a shaken mixture of oil and vinegar for salad dressing. Since fat is hydrophobic, it is not stable when exposed to water, and thus forms little globules to minimize its surface area facing water. The casein is more complex. Casein is both hydrophilic and hydrophobic, which means parts of the protein have an affinity for water while other parts are immiscible like the fat. When a molecule has both these properties, it is called amphipathic. Amphipathic molecules try to minimize the hydrophobic portions’ exposure to water and maximize the hydrophilic portions’ exposure. This way, both portions of the molecule are in the environment that best suits them. Nature has determined that a micelle structure is the best way to keep both parts of the molecule happy and stable. Micelles are little spheres of molecules that spontaneously form. The hydrophobic regions face inwards away from the water, and the hydrophilic regions face outwards towards the water. This way, both portions are in their most stable state and form an enjoyable, smooth glass of milk.
When milk curdles, it is due to the coagulation of the casein micelles and fat, with some water and its components trapped in between. Coagulation is the process of components coming together to form a solid or gel state, the same way blood proteins come together to form a blood clot (though, with different proteins thankfully). Cheesemakers force milk to coagulate by changing the amphipathic nature of casein. Casein loses its hydrophilic region, either by changing its properties or cleaving it off completely. This makes the micelles unstable. In order to minimize the new hydrophobic region’s exposure to water, multiple micelles and fat globules come together to form a larger structure and precipitate out of the water. This is the infamous and delicious cheese curd.
There are two main ways to alter the properties of casein: acids and rennet. Both of these methods were used historically and are still used today. Before the advent of sanitary standards, pasteurization, and refrigeration, milk would naturally start to sour from the bacteria found in the vats the milk was stored in. These bacteria convert the lactose to lactic acid via fermentation and cause the pH of the milk to decrease. This is similar to the way yeast converts sugars to ethanol to produce beer, wine, and spirits. When the pH of the milk drops below 4.6, the structure of casein changes such that its hydrophilic region becomes hydrophobic, which leads to micelle instability and causes milk to curdle. Early cheesemakers did not have control over this process the way they do today. Modern cheesemakers are more specific about how and when the pH is changed in order to control the water content (and thus texture) and flavor of the cheese. There are two primary types of bacteria used for this, mesophilic and thermophilic bacteria. Mesophilic bacteria thrive at room temperature and are used for mellow cheeses, such as cheddar, gouda, or colby. Thermophilic bacteria thrive at temperatures above 55°C (131° F) and are used for sharper cheeses, such as gruyere or parmesan. However, there are some cheeses that achieve a pH drop without bacteria. These cheeses are not aged and have a higher water content and thus are softer. This is because they do not form as strong of a curd because the pH shift is less pronounced without the help of the bacteria. For example, paneer is formed using lemon juice to change the pH, and is produced in a similar way to yogurt and cottage cheese.
Rennet, as mentioned previously, contains chymosin which is an enzyme that catalyzes the reaction that causes stronger curds to form. Most cheeses use both acid and rennet to create curds. The structure of kappa casein (Κ-casein) is altered by hydrolysing, or breaking, the bond between the hydrophilic and hydrophobic region of the molecule. The hydrophilic region dissolves in the water while the hydrophobic region is now exposed to the water without its hydrophilic counterpart to shield it. This is what triggers the coagulation of the micelle and fat. By coming together to form larger congregations, there are fewer molecules on the surface exposed to the water.
This change in the K-casein is a much more dramatic change than the acidification, which only alters a region of the hydrophilic portion. This is why rennet is necessary for forming stronger, tighter cheese curds with less water. In modern times, the way cheese curds form is highly controlled to achieve a specific texture and prepare the cheese for pressing, molding, and aging. The different fat, protein, and water content of the curds will change the properties of the final cheese and each subsequent step provides the cheesemaker another opportunity to control the flavor of the cheese. There are hundreds of different types of cheese made from this one simple process by altering the time, temperature, and humidity of the post processing steps. This is why different regions produce particular types of cheeses. But before the curds can be pressed into cheese, they first need to be separated from the remaining liquid, known as whey, by filtering the cheese curds in a cheesecloth or sieve.
Cheesemakers can then cut, salt, mix, or stretch the curds to create different textures and tastes. Cheddar is cut repeatedly to release more moisture. Mozzarella is kneaded and stretched in hot water to develop its stringy texture. Gouda and colby go through a water wash to create a milder flavor. The cheese is then pressed into a mold to create its final shape. During this step, cheesemakers can incorporate different spices or additives such as paprika, pepper, nuts, mushrooms, or even beer. Everything is mixed and pressed, with harder cheeses undergoing more pressure while softer cheeses have less. Historically, the cheeses were pressed into tough rinds, sealed, and aged so that they can be preserved for later use. Today, the cheese is similarly aged and ripened to enhance the flavor.
The rind can naturally develop as the cheese dries, or it can be sprayed with specific bacteria to produce different rinds. Some cheeses are also washed to encourage bacteria growth to develop the rind. Bacteria within the cheese continue to break down proteins during this the aging process and additional fungi or mold can be intentionally introduced to add different flavors. For example, blue cheese is inoculated with Penicillium, a strain of fungus, to create it’s unique taste and appearance. The cheeses can also be smoked, salted, or soaked in brine to bring out additional flavors. While the basic cheese making process is still the same as when cheese was first discovered, these additional steps have led to more varieties of cheeses.
Cheese is now also produced more consistently thanks to better technology and quality control. Previously, weather patterns and sanitation standards would cause variations between batches of cheese but thanks to climate control and analytical chemistry, industrial cheesemakers know how to create fairly similar cheeses despite changes in the environment. Today, Wisconsin has 127 cheese plants and produces more cheese than any other state. However, it was not until 1910, nearly 100 years after Wisconsin first started producing cheese, that it became the top cheese producing state.
The English Puritan dairy farmers first brought cheese to the US when they immigrated in the 17th century. They first started on the east coast, in Rhode Island, Connecticut and Massachusetts, and then settled in Vermont, New York, and Ohio. They brought the knowledge of raising cattle and producing milk and cheese with them, and immediately set up their dairy farms, with New York and Ohio quickly becoming “cheese hubs.” In the 1830s and 1840s, American pioneers expanded west via the Erie Canal and Great Lakes to southeast Wisconsin. With the vast availability of land, many immigrants opted to settle in Wisconsin in the 1840s and 1850s, specifically from Germany, Norway, and Switzerland. The only problem was the lack of cattle and cheese equipment available. While they were able to easily buy milk cows from Ohio and New York, the equipment was harder to transport and manufacture, which made it too expensive for early immigrants to afford. So, driven by the need for their food staple, they improvised.
Early Wisconsin cheese makers would use whatever vats and sieves that were close enough to their normal equipment at home. Home was a literal use of the word, as cheese making was not an industrial process yet. Most women made batches of cheese at home for the family to enjoy. Dairy farming and cheesemaking was a side business, with wheat as the main cash crop. In fact, in the mid 1800s, Wisconsin was America’s bread basket. However, as cheese became more popular and demand grew, dairy started to become more profitable. The real turning point was in 1855 when over farming and monocrops of wheat started to degrade soil quality and make the crops susceptible to pests and a bout of chinch bugs wiped out yields. The agriculture focus shifted to dairy farming and crops suitable for livestock consumption rather than human consumption.
Cheesemaking was hard work, and with increasing demand, small farms and individuals started to combine resources and milk to decrease labor. Individual dairy farmers would drop their milk off at crossroad factories where the milk would get processed into cheese. Between 1864 and 1874, approximately 53 co-op cheese factories were opened across Wisconsin. By 1880, Wisconsin was the second largest producer of cheese, in 1890 the first dairy school was opened at the University of Wisconsin, and by 1899 there were over 1500 crossroad cheese factories producing 77,858,600 pounds of cheese. Shortly after, in 1910, Wisconsin became the top cheese producing state.
Wisconsin took this responsibility seriously, and became the first state to add regulations for clean milk in 1920. In 1930, Wisconsin became America’s Dairyland, and in 1939, this title was featured on the state’s license plates. In 1985, through a series of spontaneous events, Wisconsin got its iconic cheesehead status. When the Chicago Bears won the Super Bowl, Chicago fans started taunting Wisconsin fans with the nickname “cheeseheads”. One fan took this to the next step in 1987 and created a cheese shaped hat out of the foam of his mother’s old couch and wore it to a Brewer’s game. It quickly became popular and turned into a very profitable business for the young fan.
Clearly, Wisconsin is very serious about its cheese. Wisconsin produces approximately 25% of domestic cheese and is the only state that offers the opportunity to become a Master Cheese Maker. Approximately 90% of the milk made in Wisconsin is turned into cheese to feed the nation. Wisconsin is also the leading state for recycling manure and using it as a source for renewable energy. Of course, if you live in Wisconsin, none of these facts are too surprising. After all, you don’t become America’s Dairyland and The Cheeseheads without a passion for cheese.