
How Milk Becomes Cheese
Season 5 Episode 17 | 6m 44sVideo has Closed Captions
We visit St. James Cheese Company in New Orleans to learn about the chemistry of cheese.
Ever wonder how milk becomes cheese? We asked about the science and the microbes that go into this tasty food. This week on Reactions, we visit St. James Cheese Company in New Orleans to learn all about the chemistry of your favorite dairy product.
Problems playing video? | Closed Captioning Feedback
Problems playing video? | Closed Captioning Feedback

How Milk Becomes Cheese
Season 5 Episode 17 | 6m 44sVideo has Closed Captions
Ever wonder how milk becomes cheese? We asked about the science and the microbes that go into this tasty food. This week on Reactions, we visit St. James Cheese Company in New Orleans to learn all about the chemistry of your favorite dairy product.
Problems playing video? | Closed Captioning Feedback
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So we asked Richard Sutton and Christy Caye of St. James Cheese Company in New Orleans to give us the skinny.
Cheesemaking is a process of using microbes, enzymes, and salt to make nutritious but perishable milk last longer.
"People started making cheese, humans started making cheese, whenever we did that, a long time ago.
They did that because they were looking for a way to preserve the nutritional value of milk, over the period of time when they otherwise weren't able to get fresh milk."
"Milk looks like a very simple white substance, but it's actually very complex, and a glass of milk basically has a handful of things.
There's water, there's a bunch of protein floating around in there, there's fat, there's vitamins and minerals, and and there's sugar, also known as lactose."
The trick to turning milk into cheese is removing the water while keeping most of that other good stuff, since less moisture makes it harder for spoilage microbes to grow.
And adding good bacteria and fungi makes it harder for bad ones to get a leg up.
So cheesemakers start by adding those good microbes to the milk.
Lactic acid bacteria lower the pH of the milk, which helps it to solidify, and also helps the cheesemaker control what other microbes will grow.
"Cheesemaking is a little bit like mimicking the way that we would digest milk, you know.
So if we drink milk or if you take milk from your mother... there are enzymes in your stomach that actually breaks that fluid down" Then the cheesemaker adds rennet Rennet is an enzyme that traditionally comes from the stomach of a cow, but vegetarian versions can be made from plants or microbes.
Regardless of the source, rennet starts breaking down the milk proteins, which will make it possible to separate them from the water.
The main protein in milk is called casein, and the main target of rennet is a version called kappa casein.
Casein exists in these globules with kappa casein on the surface.
Kappa casein has these very hydrophilic segments that keep the protein globule suspended in water.
Rennet chops those right off.
The casein globules lose their affinity for water, and start to stick to each other instead, and the milk proteins start to clump together.
Most of the fat, vitamins, and minerals stay with the protein.
That group of solids forms curds.
Most of the sugar drains away with the water, which is called whey.
After the rennet does its work, there are a series of steps to getting rid of the whey, bringing the moisture content down from about 85% in milk to between 30-60% in cheese, depending on whether you're looking at a nice, soft Brie or a really hard Gouda or something.
"So the more water you take out the milk, the harder cheese you're going to get but also the longer the cheese will last, typically, and the less kind of microbial activity can go on there.
So basically when you make cheese you're taking water out of milk."
But plain curds aren't all that tasty.
Aging the cheese is a crucial step to making all the delicious different kinds we know and love.
Why?
More microbes.
Mostly molds, plus some yeast and bacteria, will grow inside the cheese or on the rind.
"In regards to desirable bacteria and mold and yeast and stuff like that, cheesemakers add those in a very controlled way in which they know exactly what they're getting into.
Some are added in the milk during cheesemaking, some are rubbed on the outside of the cheese after it becomes a wheel, some cheeses are washed in a liquid that has bacteria in it or other things."
"Cheese is all about micro organisms and bacteria and molds and fungus is and all kinds of cool things.
It's alive.
I mean, cheese is absolutely totally alive."
Aging gives those microbes time to grow and develop their funky flavors.
And it's all about creating an environment where the right microbes will thrive and create the perfect cheese.
Finally, we wanted to know: If milk is white, why is cheese yellow?
Apparently, there are a couple of reasons.
"So when cows are kept on grass typically, the milk will acquire a more yellow quality because they are unable to digest the beta carotene in the grass.
And you wind up with a golden hue.
That's a good thing.
We like cows that the grass, because it makes tasty milk, and it makes tasty cheese."
Cheese can take on a natural, buttery yellow hue from beta carotene, an orange pigment and relative of vitamin A.
However, all those protein clusters scatter light and make milk look white -- the beta carotene is hidden.
Beta carotene is soluble in fat, so during the cheese making process, it stays with the solids, becoming more concentrated and more visible to the eye.
But consumers started associating that color with healthier cows and better milk, so cheese manufacturers started punching it up by adding a natural coloring agent called annatto.
Annatto is derived from the tropical achiote tree, and can be used as a mild spice -- but cheesemakers are more interested in its vivid color.
The fluorescent orange color of grocery store cheddar is an artifact of history -- not an integral part of the cheese.
"But it has been hypothesized by some that it might've been the fact the cheesemakers did that because they knew that cows that were fed and grass produce a better quality milk.
So they say well, in the winter time, maybe I'm just going to put a little something in there because it's going to look better at the market when I bring it to the market and sell it."
"They would have milk that was lovely foraged milk or whatever, because it was eating grass, and when you skim the butter fat off the top, it removes a lot of that beta-carotene in the butter so it looks lighter colored, and then basically they would add color to make it look like it was a full fat cheese...
Anything that's, any cheese that's oranger than like a buttercup yellow, or like a nice rich butter yellow, typically they're adding annatto to the cheese."
So that's how milk becomes cheese, in all its delicious, delicious glory.
"We've been eating cheese on this planet for a couple thousand years, and we'll probably do it for another couple thousand years, I hope."
Thanks for watching.
Huge thanks again to Richard and Christy from St. James Cheese Company, which you should visit if you're ever in New Orleans.
See ya next time.
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