In Wisconsin, we love our cheese curds. But how are they made? And why do they squeak?
In a state that produces more than 3 billion — yes, with a "b" — pounds of cheese annually, curds have become more than just popular. They're fast approaching an obsession.
In just the last few years, they've become staples at Wisconsin bars and restaurants, and been added to the traditional offerings at summer fairs and festivals. They even show up on some local fast-food menus.
Served raw or deep-fried, they can be tossed in spices, dipped in sauces or added as garnishes to sandwiches and tacos — and these are just the options found within the gates of Summerfest, where five vendors are offering cheese curds for the first time this year.
At the Wisconsin State Fair later this summer, about a dozen locations will offer some form of curds.
Milwaukee’s Clock Shadow Creamery sells about 80% of its product in curd form, and orders keep rising. “We’re ramping our production pretty quickly,” said head cheese-maker John Slawinski.
Ellsworth Cooperative Creamery sees the same phenomenon — each year, curds make up a higher percentage of its output.
Nationwide, dollar sales of cheese curds have grown an average 12.3% annually over the past five years, according to the Wisconsin Milk Marketing Board.
Slawinski thinks the increase in demand is because cheese curds are a perfect combination of salty and fatty, and they have a natural gimmick: When fresh, they're squeaky.
So how are cheese curds made? And what's the deal with that signature squeak in fresh curds?
Time for a little science.
Milk is mostly water. Proteins, sugars (lactose), fats and minerals like calcium constitute only 12% of cow’s milk. Cheese making requires removing most of the water from that tasty 12%.
First, the milk is pasteurized to kill unwanted microbes. Then, cultures of carefully chosen bacteria are sprinkled into the warm milk. The bacteria begin chomping down on lactose, converting it to lactic acid.
Curdling is initiated by the addition of rennet. Rennet rapidly converts milk into a cloudy gel by changing the structure of a milk protein called casein.
Normally in milk, casein proteins form "hairy" clusters by clumping together with their tails pointing outward. The dangling tails form a protective shell and prevent the cluster from interacting with other clusters.
However, an enzyme in rennet clips off the tails. The loss causes the clusters to stick to each other, explained David Montgomery, outreach specialist and assistant coordinator at the Center for Dairy Research at the University of Wisconsin-Madison.
As a result, the clusters grow larger and form chains, trapping fats as they expand into a three-dimensional network similar to a swollen sponge.
The milk gels as this network forms. Cutting and heating the gel forces the network to contract and expel water like a self-wringing sponge. Within hours small curds appear, and the expelled liquid is drained away.
Cheese-makers further assist the draining process by “cheddaring” the cheese. They slice the mass of curds into pieces and stack them like bricks. After the cheese settles, they flip the bricks and re-stack them, and then flip and re-stack them again.
Finally, the bricks are chopped into the irregularly shaped, bite-sized pieces familiar to curd fans.
Getting the squeak
Fresh curds produce the best squeaks because they are firm and rubbery thanks to the strong casein network. However, scientists have yet to precisely define how a cheese curd makes noise in your mouth.
The most likely explanation is a phenomenon called stick-slip. Stick-slip also causes chalk to screech on a blackboard, a wet wine glass to sing under a fingertip, and basketball shoes to squeak against a wood floor.
Instead of gliding in a smooth motion against your teeth as you chew, the rubbery cheese curd probably moves in extremely tiny, stuttering steps. It catches and sticks until additional pressure forces it to slip, over and over again. These quick, jerky motions generate sound waves that you hear as a squeak.
Over time, the enzymes and lactic acid in the cheese eat away at the proteins. As the network weakens, the cheese texture becomes smoother and the squeak fades.
The trade-off? The steady breakdown of proteins, sugars and fats infuse the cheese with more flavor.
Although the squeak cannot be extended indefinitely, Montgomery offers consolation for die-hard squeak fans.
“You can preserve it to some degree by freezing the cheese, essentially slowing down all the chemical reactions that break down the proteins.”