The Chemistry of Cheese: Part 2

The basis of cheese making involves a series of chemical reactions and processes that produce different types of cheese based off of the manipulation of the different elements involved. At its core, cheese is essentially made by removing the water and some minerals from milk in order to create milk curds, which is coagulated protein and fat. The water mixture that is taken away is known as whey. The way in which the curds are handled and treated affects the overall outcome of the cheese and is why there are thousands of types of cheese.

From the amount of rennet added, the way in which the rennet is added, the bacterial cultures used, and even the amount of salt used; there are many aspects of cheese making that set different types apart. The temperature that the cheese is aged in and the treating process of each cheese also effects the overall outcome of the cheese including its acidity, fat, moisture, protein, and level of calcium.

There are seven identified cheese families as outlined by Professor Arthur Hill from the University of Guelph. In the following descriptions, which come directly from his article, “Introduction to Cheese Making,” he explains the basic differences in production that set each cheese family apart.

Family 1: Acid-Coagulated Fresh Cheese. This family includes cottage cheese, quark and cream cheese and is coagulated by lactic acid produced by bacteria, with almost no contribution from rennet.

Family 2: Rennet-Coagulated Fresh Cheese. This family, including Italian fresh cheese and halloumi, is coagulated entirely by rennet and the natural pH of the milk.

Family 3: Heat-Acid Precipitated Cheese. In this family, coagulation occurs by heating the milk above 75°C which denatures the whey proteins and then acidifying by the addition of lactic or citric acid. This means that both casein and whey proteins are coagulated, creating a moist but firm cheese, such as ricotta or paneer cheese.

Family 4: Soft Ripened Cheese. This family includes Brie, Camembert, feta and blue cheese. A large amount of lactic acid bacteria is added and ripened before the addition of rennet, increasing the quantity of acid produced. Additionally the setting time is increased.

Family 5: Semi-Hard Washed Cheese - a large and diverse family including Gouda, Edam, Montasio and Oka. This cheese has the whey removed and replaced by water in order to remove lactose from the curd, which limits the amount of lactose, and hence the acidity of the cheese.

Family 6: Low Temperature Hard Cheese. These cheeses, which include cheddar and Manchego cheeses, are characterized by lower moisture and the control of lactose content by fermentation.

Family 7: High Temperature Hard Cheese. By reducing moisture content by high renneting and cooking temperature, romano, Parmesan and Swiss Cheese are produced.

As you can see, just like people, cheese comes in all different shapes and sizes. There is a cheese out there for everyone (well unless your lactose intolerant.) It is the minor differences in the process of creating cheese that can create such immense differences in the final product on your plate.

Michael Tunick, a research chemist of Dairy and Functional Foods for the USDA, summarizes the chemical makeup of cheese from start to finish in such a scientific way that, well…it is better I just quote what he wrote because I can not say it better myself…

“The milk coagulates into a curd when starter culture bacteria digest lactose and rennet enzyme destabilizes casein micelles. Cooking and piling the curd forces out whey and fuses the micelles into a matrix, addition of salt helps control microbial growth, and aging leads to protein and fat breakdown by enzymes added to the milk and produced by microorganisms, generating characteristic textures and flavors. Changes in physical chemistry of cheese may be monitored by electron microscopy and rheology, and chromatographic techniques allow flavor compounds to be identified. Differences in cheesemaking procedures lead to a wide range of varieties, which chemists study in order to provide products that are more acceptable to consumers”

The chemistry of cheese is not only important in terms of its physical makeup, but in the way it is monitored and observed as well which is clear through Tunick’s research. Just as I mentioned last week, so often we go about eating cheese or any food for that matter without thinking about how it was actually made. Tunick’s goes on to comment on this phenomenon in our culture.

“Americans consume 14 kg of cheese per capita without realizing the extent to which chemistry is responsible for the production of this food. Enzymes from starter culture microorganisms and the coagulant degrade protein (primarily casein), carbohydrates (mostly lactose), and lipids, generating the flavors and texture of cheese. Electrophoresis, electron microscopy, and rheology show that proteolysis, structural development, and functional properties depend on a number of factors, including species of animal producing the milk, processing conditions, and storage temperature and time. Goats" milk, for example, contains significantly less as1-casein, the primary structural protein in cows" milk cheese, resulting in a soft, easily fractured product. The types of starter and coagulant are responsible for development of different flavors, and the treatment of the cheese curd leads to variations in texture and melting properties. The characteristics of cheese depend on the chemistry involved in the way it is made and stored, and knowledge of this chemistry leads to the creation of a better product.”

The way in which a cheese is made is not the only process that has a direct correlation to chemistry, but the individualized taste of each cheese is affected by this science as well. Just like the appearance and the creation of a cheese are influenced by many different factors, the flavor of a cheese has many different components as well, as Tunick explains. This includes, “milk quality stemming from the diet of the animals, processing parameters such as pasteurization and addition of salt, and enzymatic and chemical reactions that occur as the cheese ages.” Ever wonder why cheese well, tastes like cheese? Tunick writes, “Lactose and citrate are metabolized by lactic acid bacteria to form a number of important compounds, including acetoin, 2,3-butanediol, and diacetyl, which generate buttery, cheesy flavors.” Or maybe even why the cow’s milk cheese you are eating has an almost grassy taste? Well Tunick continues to explain that “proteolysis of casein by coagulant, plasmin, and other enzymes leads to the production of acids, alcohols, aldehydes, amines, and amino acids, which bring about alcoholic, fatty, and green flavor notes.” However, not all cheeses are lucky enough to have a more understated smell and taste. Many people complain about “stinky” cheese, which apparently with “the breakdown of aromatic, branched-chain, and sulfur-containing amino acids also produces flavor compounds, many of which are undesirable. Triacylglycerols are lipolyzed into fatty acids, which impart pungent, cheesy flavors.” Every cheese has its own unique taste. Whether it is earthier or more intense, you will never find two cheeses that are exactly equal. This is due to the Fatty acids, which can be converted “into methyl ketones, secondary alcohols, lactones, esters, and other compounds, which are responsible for earthy, floral, fruity, and rancid flavors. An array of compounds contributes to the unique flavor characteristics of each cheese variety.”

The picture below shows the arrangement of molecules in cheese that lead to its pungent and intense smell.

From milk, to curd, to product, to the taste in your mouth, every part of the cheese process has its own unique, cheesy chemistry.

For even more information about the specific chemistry of different cheeses visit this site.

The Chemistry of Cheese: Part 1

For centuries, cheese has surfaced the tables of households and restaurants and has been a staple in many cultures throughout the world. While many of us enjoy its delicacy, whether the cheese is from Spain, France, or even Wisconsin, not many people stop to think about how the cheese they are eating was actually made. Well, now you definitely will. This post, along with next weeks post, will explore the chemical makeup of cheese.

The origin of cheese is assumed to predate any recorded history of cheese itself. The proposed date of origin ranges from 8000 BCE to 3000 BCE. At this time, many people used dried animal stomachs to store a variety of substances, such as milk. The creation of cheese was most likely an accident (a very good accident that is.) Most likely a herdsmen stored milk in one of these stomach “containers,” and when the milk was left out in the sun in the container, a chemical reaction took place. The heat caused the milk to combine with rennet, the digestive enzyme that lines the animal’s stomach, causing the milk to coagulate and create a white lump form known as curd in a water-like whey fluid.

Whey contains a 5% mixture of lactose in water as well as the dissolved aspects of the original milk. The whey and curd are separated after they are fully formed using a cheesecloth and other techniques, and the whey can then be used for other purposes such as making processed cheese. The protein matrix that remains in the curd becomes more compacted as the whey is removed. The cheese curd that is created holds much of the milks original nutritional value including the protein source of casein. The rennet forces the casein to separate from the milk and to become part of the curd. In itself, casein holds carbon, nitrogen, oxygen, hydrogen, phosphorus, and sulfur. Rennet is one of the most important factors of the chemical process of cheese creation.

“Rennet (chymosin) is a proteolytic enzyme and its role is to destabilize casein micelles and make them to coagulate. Similar enzymes are also found in plants, microorganisms, and digestive tract tissues of other animals including chickens. They break down k-casein present on the surfaces of casein micelles in milk. Deprived of the protective action of k-casein, casein micelles form a gel. When examined by electron microscopy, they form a thin matrix consisting of their clusters and short chains, encapsulating fat globules. Void spaces in the matrix are filled with the liquid milk serum called whey which is a solution of lactose, minerals, and vitamins, and a suspension of whey proteins. The subsequent steps in the cheese manufacture are aimed at separating the curd from the whey and ripening it.” (source)

In modern production (thankfully no animal stomachs are directly involved), the milk is soured and then rennet is added in order for the curds and whey to form. Every cheese has its own unique process of curdling and production. While some cheeses require the addition of acidity in order to curdle, others are just treated with rennet. The softer and fresher the cheese, the more acid is involved, while the more aged and harder forms are mainly curdled with rennet.

When the curd and whey is completely separated and the curds are combined together to form the cheese substance, a soft and almost gel-like substance is formed. After being drained, salted, and cased in wrapping, this substance is ready to be eaten. However, in order to create a firmer and tastier cheese, this gel like substance needs to be aged. During the aging process, known as affinage, microbes and enzymes cause the flavor of the cheese to become bolder and the texture to change. As the casein proteins and milk fat breakdown into amino acids, fatty acids, and amines, the cheese begins to change. Often times, additional microbes, or better known as bacteria and molds, are released into the environment of the aging facility or are put directly into the cheese in order to additionally affect it in the aging process. Bacteria and mold can also be added to cheese to adjust its flavor or pH level. From the type of animal milk to the length of aging to the amount of milk fat and even the treatment processes, creating a cheese is not always an easy feat.

So as of now we know the basics to the chemistry of cheese. Check back next week for even more about the science of fromage.

The First of Many Cheesy Posts

For my senior initiative project, I will be researching the science and art of cheese. You may think, why cheese? As many people know, cheese has been my favorite food for my entire life. When the opportunity arose to drop a class and study a topic of my choice instead, cheese seemed like the perfect subject to explore because it would allow me to turn my passion into a learning experience.  To learn more about my so-called "addiction," read the essay below that I wrote for a college application. 

They warned us about drugs and alcohol, but I guess I missed the class about cheese. I can’t resist unwrapping the salt stained plastic; breaking off a chunk of Grana Padano with a sharp planer, and salivating as the buzz overtakes my taste buds like the smell of lavender may fill your nostrils at the first site of the Sénanque Abbey in Provence. The cold creaminess of Prince de Claverolle; the lukewarm gooeyness of Brie de Meaux; even the processed stringiness of a Polly-O string cheese; they all give me the fix I need.

In kindergarten, when I was stricken with Coxsackie virus and Bocconcini-shaped bumps filled my mouth, it became too painful to suck my thumb. So, my mom melted a string cheese in the microwave for twenty-three seconds, and this warm, salty pool of cheese became the only decent substitute for my thumb. Much later, to survive chemistry, Ms. Goater offered an extra credit opportunity to create a periodic table of anything. Suddenly, science became fun as I was arranging Roquefort and Niolo into type, percentage of fat, texture, and months needed to age. While I may not be able to explain Le Chatelier’s Principle, I can tell you that Stilton is a semi-hard cow’s milk with 55% fat that takes 6 to 8 months to age and is best served with walnuts, a slice of pear, and a glass of port.

        Nothing is more enjoyable than seeing a friend enjoy a 12-month aged Manchego that I have just introduced to them. Cheese helps me bring people together, and while my life can be filled with its ups and downs, sheep’s milks and tangy blues, at the end of the day it is nice to know that the cheese and I stand alone.