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How is Cheese Made?

Emily Dilandro, Angela Hartsock
  • Author
    Emily Dilandro

    Emily DiLandro has taught college and high school Biology, Microbiology, and Marine Biology for three years. She has a Masters degree in Microbiology from the University of South Florida and a Bachelors degree from Palm Beach Atlantic University in Molecular Biology and Biotechnology.

  • Instructor
    Angela Hartsock

    Angela has taught college microbiology and anatomy & physiology, has a doctoral degree in microbiology, and has worked as a post-doctoral research scholar for Pittsburgh’s National Energy Technology Laboratory.

Learn about the cheesemaking process. Understand what is cheese made out of, and explore the role of bacteria and mold in the cheesemaking process. Updated: 12/09/2021

What is Cheese Made Out Of?

Cheese is a dairy product made out of milk that is chemically altered using bacteria and mold microbes. There are two main steps in the cheesemaking process - curdling, which includes fermentation, and aging or ripening, which is when flavoring happens. While all cheesemaking follows the same general process, each type of cheese gets its distinct flavor, texture, and color based on the different species of bacteria or mold used to create it.

The first cheeses ever made were likely created on accident. Milk was originally stored in containers made from dried calf stomachs, which were the perfect cheese-making factory. Calf stomachs, just like other mammalian stomachs, naturally had ingredients like bacterial cultures and the enzyme rennin, which caused the milk to curdle and make cheese. Today, instead of using naturally occurring microbes to make cheese, the bacteria, mold, and enzymes needed are often grown in labs.

Microbiological Safari

Let's go on a quick safari. No need for a travel agent or a lion repellant; we're going to safari in your kitchen. Hopefully, you've been so devoted to learning about microbiology that you haven't cleaned out your refrigerator or cupboards for a while.

First up, let's look at that loaf of bread that's been in the bread box for about two months. Wow. Look at all that green bread mold, likely rhizopus! Fascinating.

Mold found on bread
image of bread mold

Hey! Quick, look over there! Cheese. Or, it used to be cheese. Just look at all the many amazing colors and textures of microbes covering the surface. There could be 20 different organisms there. Just think about that biodiversity!

Mold found on cheese
image of moldy cheese

Let's dig a little deeper. Hey, I remember this bag of salad greens.

Wilted salad greens with bacteria
bowl of wilted salad greens

They're all slimy now, and, man, they stink. Sounds like the bacterium pseudomonas to me. And our next stop, a carton of milk that expired in 2008. Oh, it's chunky. Crack the lid. Smell that? Wow. I think we're about ready to make cheese.

Sour milk becomes chunky.
image of chunky soured milk

Don't laugh. This is, in essence, the first step in cheese production. I sense you don't believe me. Then I guess we need to end this impromptu safari and dive back into the world of microbiology.

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Figure 1: A block of soft cheese that has undergone curdling and ripening.

An image of a block of soft cheese.

Cheesemaking Process: How Is Cheese Made?

The cheesemaking process includes several steps to ensure the correct flavor and type of cheese is created. The first three cheesemaking steps below make up the curdling stage of cheese making and the last three steps make up the flavoring and aging stage. The specific steps of cheesemaking are:

  • Acidification: bacteria start breaking down milk
  • Coagulation: milk begins to turn from liquid into solids
  • Curd and whey: milk is separated into solid curds and liquid whey
  • Salting: curds may be salted for taste
  • Shaping: curds are shaped based on a molding form
  • Ripening: more bacteria and mold are added to curds for flavoring

Curdling in Cheesemaking

Curdling is the first stage in the cheesemaking process. Curdling starts to occur when the cheese is fermented with bacteria, making the milk acidic and changing the taste of smooth milk to sour. The acidified milk causes proteins like casein and fats to coagulate together and separate from remaining liquid. The most common bacterial cultures used during curdling are the lactic acid bacteria lactobacillus and streptococcus. These bacteria ferment the carbohydrates found in the milk, creating lactic acid. This lactic acid then helps in the process of precipitating out the proteins and fats from the milk and creating loose and soft curds.

Another ingredient that is usually used in conjunction with lactic acid bacteria to curdle milk is the enzyme called rennin. Rennin is a naturally occurring enzyme found in mammalian stomach lining that is used to break down milk. It does this using chymosin, the active ingredient of rennin. Chymosin chemically changes the protein molecules to make a more sturdy curd structure. This creates curds that are more firm and able to be manipulated into many different kinds of cheeses through the ripening or aging process. Today, rennet, or laboratory-made rennin, is often used to make cheese in place of natural rennin.

Cheese

You all should know what cheese is. Just so no one needs to ask and feel self-conscious, I'll define it. Cheese is a diverse food derived from milk, composed mainly of coagulated milk proteins and fats. It is impossible to determine where and when the first cheese was produced, but very early cheeses were likely to have been an accident. Early man often stored and transported milk in the inflated internal organs, often the stomachs, of mammals. Agitating this mixture of milk and the natural compounds found in the stomach eventually produced a rudimentary cheese, but we'll touch on that in a bit.

No one knows when this accidental cheese making started, but recent archeological findings suggest that cheese was actively being produced as early as 5,500 B.C. Pottery dating to that period found in Poland was full of holes, resembling cheese strainers. This circumstantial evidence was later supported by milk residues found on the pottery.

Today, cheese comes in hundreds of unique varieties, each with their own characteristic textures and flavors. Cheese can be made from any type of milk, which is the most important ingredient in cheese. Most frequently, cow's milk is used to make cheese. But, we still need to talk about the second most important ingredient: microbes.

Microbiology and Cheese

Without input from various microbes, your cheese would just be a smooth, white liquid, also known as milk. Turning that milk into cheese takes two steps, each dependent on very specific microorganisms.

The first step is called curdling, which is the conversion of milk into a solid mass of precipitated milk proteins and fats. This step relies on lactic acid bacteria. These bacteria are able to ferment the carbohydrates found in the milk, releasing lactic acid in the process. The lactic acid causes the proteins dissolved in the milk to precipitate, or come out of solution. When the proteins precipitate, they pull out the fats as well. What you are left with is similar to the sour milk from the introduction: the liquid whey filled with many solid chunks of protein and fat, called curds. These curds are filtered out from whey and used to make cheese. Bacterial genera like lactobacillus and streptococcus are a couple of common lactic acid bacteria.

But before we continue to the second step, let's go back in time. I mentioned that the first instance of cheese making was likely an unexpected result of storing milk in organ bladders. Often, calf stomachs were used as milk storage vessels. Lactic acid bacteria just so happens to be naturally found on decomposing plant material and would likely be present in the calf stomach already.

But, young calves also have an enzyme in their stomachs to help break down milk, called 'rennin.' Rennin is also able to precipitate milk proteins. Early, accidental cheese makers unknowingly created the perfect conditions. Milk was agitated in a sealed container containing rennin and lactic acid bacteria. Today, many cheeses rely on laboratory-manufactured rennin, called rennet, added to the milk, with or without lactic acid bacteria, to produce the curd. Cottage cheese is produced exclusively with rennet.

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Video Transcript

Microbiological Safari

Let's go on a quick safari. No need for a travel agent or a lion repellant; we're going to safari in your kitchen. Hopefully, you've been so devoted to learning about microbiology that you haven't cleaned out your refrigerator or cupboards for a while.

First up, let's look at that loaf of bread that's been in the bread box for about two months. Wow. Look at all that green bread mold, likely rhizopus! Fascinating.

Mold found on bread
image of bread mold

Hey! Quick, look over there! Cheese. Or, it used to be cheese. Just look at all the many amazing colors and textures of microbes covering the surface. There could be 20 different organisms there. Just think about that biodiversity!

Mold found on cheese
image of moldy cheese

Let's dig a little deeper. Hey, I remember this bag of salad greens.

Wilted salad greens with bacteria
bowl of wilted salad greens

They're all slimy now, and, man, they stink. Sounds like the bacterium pseudomonas to me. And our next stop, a carton of milk that expired in 2008. Oh, it's chunky. Crack the lid. Smell that? Wow. I think we're about ready to make cheese.

Sour milk becomes chunky.
image of chunky soured milk

Don't laugh. This is, in essence, the first step in cheese production. I sense you don't believe me. Then I guess we need to end this impromptu safari and dive back into the world of microbiology.

Cheese

You all should know what cheese is. Just so no one needs to ask and feel self-conscious, I'll define it. Cheese is a diverse food derived from milk, composed mainly of coagulated milk proteins and fats. It is impossible to determine where and when the first cheese was produced, but very early cheeses were likely to have been an accident. Early man often stored and transported milk in the inflated internal organs, often the stomachs, of mammals. Agitating this mixture of milk and the natural compounds found in the stomach eventually produced a rudimentary cheese, but we'll touch on that in a bit.

No one knows when this accidental cheese making started, but recent archeological findings suggest that cheese was actively being produced as early as 5,500 B.C. Pottery dating to that period found in Poland was full of holes, resembling cheese strainers. This circumstantial evidence was later supported by milk residues found on the pottery.

Today, cheese comes in hundreds of unique varieties, each with their own characteristic textures and flavors. Cheese can be made from any type of milk, which is the most important ingredient in cheese. Most frequently, cow's milk is used to make cheese. But, we still need to talk about the second most important ingredient: microbes.

Microbiology and Cheese

Without input from various microbes, your cheese would just be a smooth, white liquid, also known as milk. Turning that milk into cheese takes two steps, each dependent on very specific microorganisms.

The first step is called curdling, which is the conversion of milk into a solid mass of precipitated milk proteins and fats. This step relies on lactic acid bacteria. These bacteria are able to ferment the carbohydrates found in the milk, releasing lactic acid in the process. The lactic acid causes the proteins dissolved in the milk to precipitate, or come out of solution. When the proteins precipitate, they pull out the fats as well. What you are left with is similar to the sour milk from the introduction: the liquid whey filled with many solid chunks of protein and fat, called curds. These curds are filtered out from whey and used to make cheese. Bacterial genera like lactobacillus and streptococcus are a couple of common lactic acid bacteria.

But before we continue to the second step, let's go back in time. I mentioned that the first instance of cheese making was likely an unexpected result of storing milk in organ bladders. Often, calf stomachs were used as milk storage vessels. Lactic acid bacteria just so happens to be naturally found on decomposing plant material and would likely be present in the calf stomach already.

But, young calves also have an enzyme in their stomachs to help break down milk, called 'rennin.' Rennin is also able to precipitate milk proteins. Early, accidental cheese makers unknowingly created the perfect conditions. Milk was agitated in a sealed container containing rennin and lactic acid bacteria. Today, many cheeses rely on laboratory-manufactured rennin, called rennet, added to the milk, with or without lactic acid bacteria, to produce the curd. Cottage cheese is produced exclusively with rennet.

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Frequently Asked Questions

How is cheese made naturally?

Cheese is made naturally when milk is stored in containers made of dried mammalian stomachs like calfs and sheep. This is due to the natural lactic acid bacteria found in the stomach liners as well as other microbe contaminants that change the milk into ripened curds.

How is the cheese made?

Cheese is made in two main steps using milk and mold and bacteria microbes. The two main steps are curdling of the milk and aging or ripening of the curds over time.

What bacteria is used to make cheese?

There are many different types of bacteria used to make cheese depending on the type of cheese being made. The most common bacteria used is lactic acid bacteria.

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