There are few things as quintessentially Wisconsin as enjoying a fresh, squeaky cheese curd. Given the popularity of this delicious snack, it’s not surprising that many consumers around the country are interested in experiencing the squeaky treat. Unfortunately, due to the short window in which cheese curds stay fresh and squeaky, many individuals living outside of Wisconsin cannot enjoy the unique delight. Thanks to consumer requests and feedback from the industry, however, Wisconsin Center for Dairy Research staff are now studying cheese curds in order to find a way to extend the squeak.
So what is a cheese curd and how is it made?
Before discussing the secret of the squeak, it’s important to understand what constitutes a cheese curd and how a cheese curd is made. From a traditional standpoint, most cheese-curd purists believe that cheese curds are the result of the Cheddaring process. The Cheddaring process essentially follows the basic steps of adding culture, color and rennet to warm milk and then allowing the curds to settle into a mass. The cheese mass is then cut into “loaves” and stacked and turned by hand. The loaves are then placed into a mill, when the cheese pH reaches about 5.4. The mill cuts the cheese loaf down into pieces that are about 1.5-inch to 2-inch cheese curds. The warm milled curd is then salted and can be enjoyed right away, but the squeak will only last for a few days. Also, note that there are less traditional cheese curds that can be made out of brick, such as Muenster and Monterrey Jack, but they also have similar issues with maintaining their squeak.
In terms of standards, Cheddar curds are subjected to a standard of identity, but in general there is not a standard of identity for cheese curds. There are, however, some attributes that are used to judge cheese curds in a contest. Essentially a good curd will be fresh, meaning that it has retained its squeak and has a good shape. Additionally the cheese should have a fresh, milky and salty flavor and be void of any flavor or physical defects. Generally in competition the curds must have been made within the past day or two. While they will be refrigerated, the curds must be tempered to room temperature before consumption because the warmth is needed to create the squeak. While we will discuss the use of microwaves in tempering a cheese curd from refrigeration, most competitions do not currently allow curds to be microwaved prior to judging.
The story of the squeak
So where does this squeak come from? In the simplest terms, the squeak in cheese curds is created when teeth compress the protein network in the cheese and it resists but then rebounds as teeth pass through it. The rebound is what generates vibrations and causes the squeak.
The more complicated version of that answer involves the attributes of casein, the protein in cheese, and its ability to bind with calcium. To clarify, casein molecules are often called the building blocks of cheese because they form its physical structure. In cheese, these molecules of casein are held together by calcium phosphate. In a fresh cheese curd, the casein is very tightly knit, connected by a high number of these calcium phosphate molecules, allowing the protein network in the cheese to resist our teeth and rebound in order to create the squeak. Time, however, is not on the side of the curd manufacturer as the acid in the cheese from the cheesemaking process will slowly break down the calcium phosphate bonds. This weakens the micelles and causes the curd to lose its ability to squeak. In other words, when cheesemakers add bacteria to ferment lactose into lactic acid, the resulting lactic acid will dissolve some of the calcium phosphate bonds, eventually resulting in a network of protein that is softer. Keep in mind that it may take a few days for enough calcium phosphate to be dissolved by the acid but once this occurs, the squeak is lost and may not be restored even if the cheese is warmed.
Cold temperatures are also the enemy of the cheesemaker as cooling the cheese will cause a change in the structure which will in turn cause the sqeak to disappear. Center for Dairy Research studies show, however, that warming the cheese forces the protein molecules to interact more closely, enhancing their ability to resist and then rebound recreating the curd’s ability to squeak. It is important to note, however, that excessive heating, 4 oz. of cheese at more than 20 seconds in a 1,100 watt microwave, will alter the protein network so that the squeak may not return.
The final enemy of the squeaky curd manufacturer is the process of proteolysis, or the breakdown of the protein in the cheese. To make cheese curds, cheesemakers add a milk clotting enzyme called rennet to the milk, which causes proteolysis to occur. If proteolysis is too extensive the squeak is lost. While it will likely take a couple of weeks for this to occur, it is irreversible.
To obtain the above information, Center for Dairy Research staff conducted a number of experiments with cheese curds. In particular, researchers were interested in prolonging the freshness and squeak of the curd. Refrigerating the curds and then reheating them in the microwave was one of the first methods tested. Researchers decided to store fresh cheese curds at 450 Fahrenheit for three weeks and then test them for mouth-feel and squeakiness. By testing the curds at various points during the three week study, researchers were able to analyze the point at which the squeak disappeared. What they discovered was that by microwaving 4 oz. of the curd for 15 seconds, the squeak could be recovered for up to two weeks. The cheese curds could also still be stretched when hot. After two weeks of refrigerated storage, however, the curds did not recover the squeak, even after they were microwaved. The curds also started to flow or melt by that time due to proteolysis and loss of calcium phosphate.
The second experiment involved freezing the cheese curds. This time, the researchers checked for squeak at one, two and three months. Before testing, the curds were thawed in the refrigerator and then held in refrigeration for up to three weeks. Again, researchers discovered that after being frozen for one, two or three months and then refrigerated for up to two weeks, the thawed/refrigerated curds were able to regain their squeak after 4 oz. were heated for 15 seconds in a 1,100 watt microwave. Regardless of the time the curds were frozen, researchers could not regain the squeak in curds that were held in refrigeration for more than two weeks.
How to prolong the squeak
What this study shows is that storing cheese curds at refrigerator or freezer temperatures can help to extend shelflife from a few days to about three and a half months. This is likely the case because the cold temperatures reduce the proteolytic activity. Additionally, researchers also believe that minimizing rennet additions and lowering acid production during manufacture can also improve the squeak shelf-life of fresh curds.
A Final Note
One interesting observation that was made during the cheese curd study is that warmed Juustolepia cheese does not lose its squeak, even after months of refrigeration. This is true because the manufacture of this cheese requires the use of rennet only and there is no acidification of the milk or cheese. The curds are pressed together into a block, cut into slabs, and then the slabs are baked in an oven. If properly baked, the rennet is destroyed preventing further proteolysis. Basically, because there is no acidification, there is no loss of calcium phosphate and with no proteolysis the squeak is maintained almost indefinitely in refrigerated Juustolepia. This observation confirms the researchers’ belief that it is the loss of calcium and eventual proteolysis that is contributing to the loss of squeak in cheese curds. Keep in mind, however, that Juustolepia cheese will also lose its squeak if the baking process is insufficient and does not destroy the rennet. The take-home message is that cheesemakers can freeze cheese curds immediately after they are made, ship them all over the country, and thaw them as needed. This might including selling the curds on the same day to consumers, or even selling the curds to consumers frozen and allowing the consumers to thaw the curd. Either way, as long as the curds follow the timing outlined here and are allowed to thaw, the squeak should remain as fresh as a curd from the vat.