The weird science of cheese

  • 03 Mar 2014

Cheese is not just food, it's a variety show. The multitude of aromas, flavours, and textures found in cheeses throughout the world is more than we encounter with any other food. It comes in hundreds of varieties; even within a variety, differences are noticeable. And it's a food that provides nutrition in the form of vitamins, minerals, and a high-quality source of protein that can be kept for months.

The science behind the transformation from plants to milk to cheese is amazing. In fact, cheese has much in common with wine and beer: they result from <a href=""

target="_blank">fermentation</a> by microorganisms; they are "value-added" products where processing greatly increases the value; and they reflect local climate and terrain. Cheese has fascinated humanity for a long time, inspiring people to refer to it as everything from "the wine of foods" (Vivenne Marquis and Patricia Haskell) to "milk's leap toward immortality" (Clifton Fadiman).

Why is cheese yellow?

Studies have shown that colour -- more so than labeling and even actual taste -- affects our expectations and perceptions of food flavour, and cheese is no exception. Even though the fat contents and flavors in orange and yellow cheddar are identical, some people perceive the former to be richer than the latter.

Annatto is what gives cheese an orange or more pronounced yellow colour. It comes from the achiote (Bixa orellana) tree found in Mexico, the Caribbean, and the western portion of South America. Annatto's major component bixin and much of its molecular structure is similar to that of β-carotene, the compound that gives carrots their orange colour. Cows transfer carotenoids (β-carotene and related compounds) from their diet to the milk, where they bind to the fat. This yellow colour is not visible since the fat content of milk is less than 4% and the carotenoid concentration less than 0.1%, and the fat globules are surrounded by casein. But most of the whey is lost during cheesemaking, causing the fat and carotenoid contents to increase, and the casein network to loosen up -- revealing the fat so the resulting cheese takes on a yellow colour.

Goats, sheep, and water buffalo do not pass carotenoids to milk (converting it to vitamin A instead), so their cheese is white. The additive for white cheese such as mozzarella is titanium dioxide -- a mineral commonly added to toothpaste -- which masks colour. Other cheese additives that bleach color are hydrogen peroxide and benzoyl peroxide.

Can you make cheese from human breast milk?

That is the strangest question I have ever been asked about cheese -- and it's been asked several times. Breast-feeding mothers often have milk left over, and people sometimes wonder what can be done with it. Perhaps make some sort of cheese from it?

But the answer is no, because the milk won't coagulate properly.

Breast milk alone can't be made into cheese because it contains too little protein (only 1%), and only some of the protein is casein.


A French web site, Le Petit Singly, advertises that they have made cheese from "breast milk of woman" since 1947. But if you try to order some online, you'll be sent to a page asking if you are crazy. That's when they admit it's a hoax (though some news outlets reported on the "company" without discovering it's a joke). And if you do have surplus breast milk, best to donate it to a breast milk bank, where it will be used to feed infants in neonatal intensive care units.

Why are some people told to avoid raw-milk cheese?

The Centres for Disease Control (CDC) and the US Food and Drug Administration (FDA) recommend that children under five, pregnant women, and people with immunodeficiency problems or chronic disease should not consume raw milk products. Yet many cheese connoisseurs -- who often refer to pasteurised milk cheeses as "dead cheese" -- believe pasteurisation not only kills off pathogens, but also the naturally occurring bacteria that contribute to flavour and might convey health benefits.


But much raw milk comes from certified dairies that have to undergo stringent sanitation requirements and testing. In the US, cheese made from raw milk must be held for at least 60 days. Any pathogens in the milk should die out during this time, and the acidity generated by the cheesemaking process will prevent pathogens from the environment from taking hold. Raw milk cheeses from outside the US must also follow this requirement or they cannot be imported.

Where do the holes in cheese come from?

The holes in Swiss-type cheeses are created when Propionibacterium freudenreichii subspecies shermanii metabolises lactic and propionic acid.


The CO2 gas accumulates at the weaker spots in the cheese matrix, forming the bubbles that we call "holes" or "eyes." Some 120 litres (32 gallons) of carbon dioxide are generated during ripening of a 175-pound wheel of Swiss cheese. About a third of the of the gas escapes into the air, half of it stays dissolved in the curd, and the rest forms the eyes.

Can lactose intolerant people eat cheese?

Affecting roughly 65 percent of the world's population, "lactose intolerance" is the inability to break down and therefore digest the lactose molecule (it's different from "milk allergy", an adverse reaction to one or more proteins in milk, that is mediated by the immune system). Lactose cannot be absorbed by the body unless you retain the lactase enzyme β-galactosidase, which splits the lactose molecule into glucose and galactose in the small intestine. If lactase is not present, the lactose moves to the large intestine where bacteria metabolise it, generating uncomfortable gas in the form of carbon dioxide, hydrogen, and methane, as well as drawing water from the intestinal wall -- causing diarrhea.


Almost everyone in northwestern Europe is "lactase persistent", but the number decreases as one goes south and east. Milk fat residues in pots found in Libya indicate processing of cow's milk there between 5200 and 3800 BC, supporting a theory that lactase-persistent people and their cattle moved from Europe into Africa during that period. As a result, some African and Middle Eastern populations can digest milk. Most Eastern and Southern Africans cannot, and many in Asia and Australia are also unable to do so. But one way to avoid lactose-related problems is to eat cheese -- because nearly all of the lactose in cheese is removed during manufacturing and aging.

What's the difference between making cheese and yogurt?

Like cheese, yogurt ("to thicken" in Turkish) is produced using starter cultures -- usually Lactobacillus bulgaricus and Streptococcus thermophilus and sometimes including bifidobacteria and Lactobacillus acidophilus.

Unlike cheese, however, milk for yogurt is initially heated to 185 degrees for 30 minutes or 200 degrees for 10 minutes, which kills off any pathogens and causes the milk protein to "denature" or fall apart. By doing this, the milk thickens (yogurt) instead of forming curds (cheese). The starter is added after the milk is homogenised and cooled to 110 degrees, and the temperature is held there for 2-3 hours. The result is a gel with a pH of 4.5 (remember, 7.0 is neutral). To compare this to cheese: milk has a pH around 6.6, meaning it is slightly acidic, and once that pH is decreased by around 0.2-0.3 units is when rennet is added to coagulate or set the milk into curd.

With yogurt, effort isn't made to remove whey -- except for in Greek yogurt, which is strained to remove whey and produce a thicker product. A pound of milk is needed to make a pound of regular yogurt ... but four pounds are required to obtain a pound of strained yogurt.

Why are certain varieties of cheese made in specific places?

Here are some examples of cheeses named for their originating regions: -Asiago comes from the Asiago plateau in Northern Italy

-Brie was birthed in the Brie region east of Paris

-Camembert is named after a village in Normandy

- Cheddar was first produced in Cheddar, Somerset County

-Gorgonzola is named after an Italian town near Naples

-Gruyère is named after a town in Switzerland

-Havarti is named after a farm north of Copenhagen

-Munster is named after a village in Alsace, France

-Roquefort is made by seven companies in and around Roquefort-sur-Soulzon, France (if a similar cheese comes from outside that area, it must be called something else, such as "blue cheese")

-Swiss cheese originated in Switzerland's Emmen valley, which is why it's called Emmental or Emmentaler


And one northern Italian bank maintains 300,000 wheels of Parmesan, worth $200 million (£119 million), as collateral for loans.

Besides tradition, another reason for the "location, location, location" phenomenon in cheese has to do with the economics of terroir (from the French for "land"). The terroir factors affecting cheese flavour include vegetation, climate, animals, season of the year, altitude, soil, and microorganisms. In the US, one aspect of the economics is the back-to-the-land movement, which provided incentive for dairy farmers to produce artisanal cheeses with a "sense of place." Another economic facet is the ability to sell in a far-off market. Before refrigeration and automobiles, Vermonters came to realise that a sturdy cheddar would survive the trip to the lucrative New York market better than a high-moisture cheese that aged quickly; Vermont specialises in cow's milk cheddar to this day.

Why do fresh cheese curds squeak?

Bite-size cheese curds that have not been pressed or aged will emit a squeak when you bite into them -- especially if they are less than a day old.


You can observe a similar effect by pulling your wet hair between your fingers after shampooing it. The detergent in the shampoo removes the oil from our hair, so our fingers don't glide smoothly, but "skip" along wet strands. The outer surface of hair is also protein, primarily keratin -- but this time it's our fingers that do the vibrating.

Why is it good to be "the big cheese," but bad to be "cheesy"?


The British picked up on it when they controlled the area starting in the 18th century, and by 1818 incorporated it in a phrase "the real cheese," meaning "the real thing." Hotten's Dictionary defines cheese and cheesy as "a first-rate or very good article." Cheese also features in the expression "the big cheese," meaning a boss or very important person. But sarcastic use of the word turned it into a pejorative, with the adjective "cheesy" being recorded in the negative sense in 1896.

Speaking of big cheeses (literally), a Cheshire cheese weighing 1,235 pounds and using the milk of 900 cows was once sent by sleigh for 500 miles from Massachussetts to Washington, DC, and presented to President Thomas Jefferson on 1 January, 1802. Inscribed with "Rebellion to tyrants is obedience to God," it was called the Mammoth Cheese due to the discovery of mammoth (now known to be mastodon) bones the year before. Cautious of accepting free gifts, Jefferson paid $200 (£119) for it and displayed it in the East Room for a year. Not to be outdone, supporters of President Andrew Jackson made a 1,400-pound cheese for him in 1837.


Edited and adapted from <a href="" target="_blank">The Science of Cheese</a> by Michael H. Tunick, with permission from Oxford University Press USA. Copyright Oxford University Press, 2014.

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