The other day, I grabbed a carton of milk from the refrigerator for my bowl of Rice Krispies. When I poured the milk, I did not hear the “snap, crackle, pop” I’d been expecting. Instead, I heard a plopping sound as clumps of white, smelly goo covered the cereal. When I looked at the carton more closely, I saw that the milk was two weeks past its expiration date. So instead of milk, I had poured a crude form of cheese on my cereal.
But that mishap didn’t go to waste. It gave me the idea to write about cheese.
Most people know that cheese is made from milk. In the United States, milk usually comes from cows. However, in some parts of the world, people get dairy products from goats, buffalo, sheep, camels, reindeer and even yaks.
So how does a bucket of milk become cheese?
Milk contains two types of proteins: casein and whey. The reason expired milk becomes “cheesy” is that bacteria in the milk grow rapidly when it gets old. The bacteria digest the milk sugar (lactose), producing lactic acid as a result. Lactic acid causes the casein to curdle, or separate into lumps, and gives the milk a sour smell.
Cheese is made the same way — by curdling milk — except the milk is curdled on purpose.
Most cheese is made in factories. After milk is poured into big vats, a “starter culture” of bacteria is added to convert the lactose into lactic acid. Then an enzyme called rennet is added to curdle the milk. In the past, rennet was obtained from the stomachs of young cows. Nowadays, cheesemakers get it from bacteria and yeast that have been genetically “taught” to make the enzyme.
Once the casein has curdled, whey protein is left behind as a thin, watery liquid. (Perhaps that reminds you of a certain nursery rhyme: "Little Miss Muffet sat on a tuffet, eating her curds and whey. . . .")
The whey is removed, salt is added, and the curds are cut into smaller pieces and heated to release more whey. The additional whey is drained off, which leaves clumps of casein. Those clumps are pressed into molds and left to age (dry) for various periods of time.
The way a cheese looks, smells and tastes depends on many factors, including the animal that produced the milk, what the animal was fed, which bacteria were used in the starter culture and how the cheese was processed.
Here are three additional fun facts about cheese:
• Mozzarella cheese has a stringy quality because it’s kneaded like dough before being formed into its final shape.
• Swiss cheese is made with bacteria that produce carbon dioxide (CO2) when they digest lactose. The bubbles of CO2 are what create the holes in the cheese.
• It's not a coincidence that some cheese smells funky. Limburger cheese, one of the stinkiest varieties of all time, gets its smell from the same bacteria that cause stinky feet — Brevibacterium linens. Some people don't mind the smell. But if Mom or Dad brings home a block of Limburger, be prepared to hold your nose.
Bennett is a Washington pediatrician. His Web site, www.howardjbennett.com, includes past KidsPost articles and other cool stuff.
FAQs
Cheese is made the same way — by curdling milk — except the milk is curdled on purpose. Most cheese is made in factories. After milk is poured into big vats, a “starter culture” of bacteria is added to convert the lactose into lactic acid. Then an enzyme called rennet is added to curdle the milk.
Why was milk initially turned into cheese? ›
The production of cheese predates recorded history, beginning well over 7,000 years ago. Humans likely developed cheese and other dairy foods by accident, as a result of storing and transporting milk in bladders made of ruminants' stomachs, as their inherent supply of rennet would encourage curdling.
How do bacteria turn milk into cheese? ›
The bacteria ferments the lactic acid of the curds into acetic acid and propionic acid, which provides flavor, and carbon dioxide, which creates the characteristic holes. In other cheeses, molds from the genus penicillium are seeded on the surface of the curds.
Do spores turn milk into cheese? ›
Molds are used to make certain kinds of cheeses and can be on the surface of cheese or be developed internally. Blue veined cheese such as Roquefort, blue, Gorgonzola, and Stilton are created by the introduction of Penicillium roqueforti or Penicillium roqueforti spores.
What is it called when milk turns into cheese? ›
Cheese is made the same way — by curdling milk — except the milk is curdled on purpose. Most cheese is made in factories. After milk is poured into big vats, a “starter culture” of bacteria is added to convert the lactose into lactic acid. Then an enzyme called rennet is added to curdle the milk.
Is cheese made from milk True or false? ›
Cheese is made by fermenting the milk, so is a dairy product. Other dairy products include butter and cream. Q. X = -5 can this be expressed as a linear equation in two variables?
Is cheese unhealthy for you? ›
REALITY. You don't have to cut cheese out of your diet, but if you have high cholesterol or blood pressure, use high-fat cheeses sparingly. A 30g portion of cheese provides seven per cent of your daily calories and there can be more salt in a portion of cheddar than in a packet of crisps.
Is cheese mold or bacteria? ›
Cheese teems with bacteria, yeasts and molds. “More than 100 different microbial species can easily be found in a single cheese type,” says Baltasar Mayo, a senior researcher at the Dairy Research Institute of Asturias in Spain. In other words: Cheese isn't just a snack, it's an ecosystem.
Is it possible to make cheese without bacteria? ›
Exceptions to this include cheeses such as queso fresco or queso blanco (traditionally eaten in Latin American countries) and paneer (traditionally eaten in India), which are made without bacterial cultures or rennet.
Can I make cheese from old milk? ›
Turns out, you probably have everything you need to make cheese in your kitchen right this minute. When faced with a carton of old milk and a few tablespoons of vinegar you can actually repurpose the liquids into a snack: in this case, a crumbly or creamy cheese.
After opening, you can safely store most soft cheeses in the fridge for at least 7 days and most hard cheeses for 3–4 weeks. Carefully inspect hard cheeses for mold and cut off any spots, but toss soft cheeses and crumbled, shredded, or sliced cheeses (whether hard or soft) if you see mold.
How was cheese made in the old days? ›
Cheese may have been discovered accidentally by the practice of storing milk in containers made from the stomachs of animals. Rennet, an enzyme found in a stomach of ruminant animals, would cause the milk to coagulate, separating into curds and whey.
How did they discover rennet? ›
The existence of animal rennet was discovered by chance around 7000 years ago, when the milk was transported using waterskins made from the stomachs of ruminants.
How do enzymes turn milk into cheese? ›
The enzyme, rennet, is found in ruminant stomachs. When added to milk, it causes the milk to coagulate and separate curds (solid proteins) from whey (liquid). This means when someone would store milk in a ruminant stomach (a common practice before glass and plastic), their milk would turn to fresh cheese.
Why isn't yogurt cheese? ›
Most yogurt and kefir (yogurt's bubbly sister) aren't drained. Instead, the milk is cultured and ripened to the point where the microbes produce enough acid to curdle the milk into a custard-like curd.
Why does milk turn into butter? ›
Milk is made up of fats and liquids. When it is shaken or beaten for a long time, the solids break apart from the liquids and attract to each other. The end result is a solid fat-based product, butter, and a liquid with a low amount of fat in it, buttermilk.
