Why do Cheese Curds Squeak?

Before we wrap up our two week look at the science of the dairy state, I thought it would be fun to share one last dairy fact that I’ve learned about during my time as a science writer in Wisconsin. I hope you enjoy and be sure to check back next week as we discuss the latest in science education.

 Why do Cheese Curds Squeak?

The Curd:

As we discussed last week, cheese curds are formed during the final stages of the cheesemaking process. While cheese curds can go on to become blocks of Cheddar, Brick or another cheese, some cheesemakers choose to stop the process a little early and allow customers to savor the warm, squeaky joy of a fresh cheese curd.

 Here in Wisconsin, fresh cheese curds are an iconic treat. In fact, there are stories of people lining up outside of cheese plants in the morning when the fresh curds are made just to get a bag of this squeaky, salty snack. After biting into this unique treat, one of the first questions many people ask is why does the cheese squeak when I bite down on it? In fact, as a science writer in the food world, this is one of the most common questions I see come through my email. So, here's a quick look at the science behind the squeak. Enjoy!

The Squeak:

At a basic level, the squeak in cheese is caused by the compression of protein networks. In other words, when you bite down, the strong protein networks in the cheese resist your teeth and then rebound as you bite through resulting in a squeak. Of course, it’s a bit more complicated than that so here’s a basic breakdown. 

Cheese contains a protein called casein which is often called the building block of cheese. These casein proteins are bonded together by calcium phosphate molecules which help to give cheese its structure and strength. In a fresh cheese curd the bond between the calcium and the casein is very tight which is why a fresh cheese curd has that strong resistance and quintessential squeak. Over time, however, the calcium bonds are dissolved by the acid in the cheese, thanks to a process known as proteolysis.

While the name sounds complicated, it is essentially a term used to describe the breakdown of proteins. In an aged cheese proteolysis is good because the breakdown of proteins aids in flavor development, but in a cheese curd it is bad as the weakened protein bonds will no longer resist teeth and create that chewy, squeaky feeling that is so loved by cheese curd connoisseurs. Proteolysis happens quickly in cheese curds. In fact, a typical cheese curd will lose its squeak within two to three days, which means that only those individuals living near cheese plants can enjoy this tasty treat.

Researchers at the Center for Dairy Research have been working to study the science of the squeak, however, and recently discovered that proteolysis can be slowed by refrigerating or freezing the curd.  This is exciting because slowing proteolysis in the curd would allow cheesemakers to transport the curd, thereby sharing  this iconic food with those outside of the state.

So there you have it, the science of the squeak.

Still hungry for more? Be sure to check out the Dairy Pipeline, Vol. 28. #3 (available later this week at https://www.cdr.wisc.edu/pipeline) to learn more about the  research discussed above.


And, be sure to check back Friday as we learn about a local elementary school who has taken science education to the next level.

Finding a Whey: How Science Changed the Whey Industry

Last week we learned that whey is one of the byproducts of cheesemaking. To clarify, there are two types of whey, one is called sweet whey and is the byproduct of Cheddar and similar style cheeses. The other is acid whey which is a byproduct of Greek yogurt and cottage cheese. Today, we will be discussing sweet whey, the byproduct of Cheddar-style cheeses.  While the term byproduct might not sound very important, keep in mind that for every 100 pounds of milk, a cheesemaker can expect to get 10 pounds of cheese and 90 pounds of whey. That 90 pounds of whey, which is drained off from the cheese, contains 94 percent water and about 6 percent solids (protein, fat, minerals and lactose). What to do with that large amount of watery whey has long been an issue for the industry but this week we are going to discuss the newly discovered benefits of this versatile dairy derivative.

Liquid whey (Picture provided by Wisconsin whey processing researcher Dr. Karen Smith

                     

Sweet Whey, A Hero in Disguise:

Once upon a time, not so very long ago, cheesemakers were burdened by large amounts of sweet whey. Though it was considered best practice to feed the whey to the pigs or use it on the fields, some cheesemakers were producing so much cheese, and therefore whey, that they were having to pay others to take the whey. All in all, whey was a financial loss for the cheesemakers and a burden to large cheesemaking communities. Along the way, however, farmers began to notice something special about this seemingly burdensome byproduct. It appeared that the pigs ingesting the whey had improved growth rates.  Researchers took over from there and it was discovered that the proteins in whey are some of the most nutritionally complete proteins known to mankind.

A picture of liquid whey provided by Wisconsin whey processing researcher Dr. Karen Smith. On the left is whey from a  cheese without added colorant, on the right is whey from a cheese made with annatto (see last week's article for more on annatto).

             
The Nutrition Factor:

So what does nutritionally complete mean? Well, aside from the 94 percent water, which is now removed during processing, whey contains 6 percent solids. These solids include fat (phospholipids), lactose (milk sugar), minerals such as calcium, phosphorus and potassium and finally protein. While each of the components are important in their own right, the protein is a key part of the nutritionally complete definition. To give a bit of background, proteins are comprised of amino acids. There are generally 22 amino acids present in the body with nine of those falling under the category of essential amino acids, meaning they cannot be produced by the body and must be eaten in the diet. Of these essential amino acids there are some called branch chain amino acids such as isoleucine, valine and leucine. Recent research has shown that these branch chain amino acids are directly linked to muscle synthesis and recovery. What’s most exciting about whey is that it contains the highest amounts of these branch chain amino acids found in food. In particular, a 2007 study from McMaster University showed that as little as 10 grams of whey protein ingested in a recovery drink will aid in muscle protein synthesis (i.e. recovery and growth). This ability to aid in muscle recovery is why you’ve likely heard of athletes drinking whey protein recovery drinks. Keep in mind that whey is not reserved for athletes. In fact, many of the professionals I’ve worked with have said that everyone from growing teens to the elderly can benefits from the complete protein package found in whey.

         A photo of whey after it has been processed. Tera'swhey (shown here) is made in Wisconsin and can be added  to milk, water or smoothies.

So, how is this processed?

After the whey is drained from the cheese any cheese fines are removed and then the whey is cooled per the legal requirements and stored in tanks. When the processor is ready for the whey it will be sent through a pasteurizer and then a membrane separation system that works kind of like a sieve retaining the proteins and letting through the smaller components in the whey.  In order to remove the water from the whey, the remaining components are sent through an evaporator and dried into powder form. This powder is then sold in stores or further processed into drinks and other products. Since the type of membrane separation varies depending on the desired outcome there are several types of whey protein powder including whey protein concentrate (WPC) 34, WPC 80 and whey protein isolate which is higher in protein and lower in fat and minerals than WPC. Depending upon the functional and nutritional needs of the final application, WPC or WPI may be used as each offer slightly different benefits and challenges in terms of food science and diet.

So there you have it, the science of whey! Isn’t it amazing how a little bit of science can take something that was once a waste product and help people transform it into a something that is now a value added product, bring profit to the cheesemaker and great nutrition to the consumer.

Be sure to join us Monday for the final story on the science of dairy.

The Cheesy Side of Science

Growing up in Wisconsin, I have become well versed in the many flavorful cheese varieties available in the Dairy State. Before working as a science writer, however, I had no idea that cheesemaking was such a highly scientific process. So, today I want to take a moment to share some of the things I’ve learned with our Curious Community. After reading this you’re sure to appreciate that next piece of cheese even more!

*Special Note: This is a fun overview of the cheesemaking process, but this list in no way covers all of the necessary steps or science involved in cheesemaking. Those interested in making their own cheese should contact a professional or a research center for guidance.

Also, while it is appropriate to use cheesemaking or cheese making, have decided to use “cheesemaking” as that is the form preferred by my sources.

The Process:

 Cheesemaking is a fairly complex process. From the addition of starter cultures and rennet to the monitoring of moisture, temperature, pH and more, cheesemakers are both chemists and artists. Though there are a few basic steps required in the cheesemaking process, the possible variations at each step make an exact outline of the process nearly impossible to create. So, instead of exploring each and every step of the cheesemaking process, we will be exploring some of the more interesting scientific processes involved in each of the basic steps of cheesemaking.

Quality Milk:

If we’re going to talk about cheese we have to talk about milk. Every cheesemaker will tell you that the secret to a great cheese is starting with quality milk. That means selecting milk from farms that are passionate about animal care and good sanitation practices.

Once the milk arrives at the cheesemaking facility, many cheesemakers will choose to pasteurize the milk to minimize the number of potential pathogens which might contribute to spoilage down the road. The pasteurization process is generally accomplished through High Temperature Short Time (HTST) processing where the milk is held at temperatures around 161 degrees Fahrenheit for about 15 seconds. For more on this see: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=133.3

Some cheesemakers do choose to utilize raw milk for their cheese. This may be done for a variety of reasons, but regardless of the reasoning, every raw milk cheese made in the United States must be labeled as such and be aged for a minimum of 60 days to ensure food safety. For more on these regulations please see the section on Cheddar Cheese at: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=133.3

Step 2:  Addition of the Starter and the Coagulant

Once the milk is ready for the cheesemaking process it will be transferred into vats and various additions will be made to aid in flavor development, color and coagulation. We won’t go into all of the details here as there are many combinations of enzymes, cultures and such that can be added to create each cheese, but one thing remains the same for all cheese, a coagulant must be added.

So what is a coagulant? Well, the terminology is a bit confusing but essentially, a coagulant is something that causes clotting. In the case of cheese, the term for a clotting agent is rennet. Rennet is then used as an overarching term for all of the enzymes that aid in coagulating milk. While rennet can come from a number of sources, the most common enzyme, or rennet, used in the coagulation of U.S. milk is fermentation produced chymosin.

Chymosin is traditionally known as one of two enzymes that help calves to process their mother’s milk. As ancient cheesemakers looked for ways to preserve milk (i.e. the cheesemaking process), they noticed the clotting power of this enzyme and began using it to jumpstart the processes of preservation.  While chymosin was originally discovered in the stomach of calves, scientists have discovered that by inserting the chymosin gene into bacteria, yeast or fungi cells and then extracting, purifying and standardizing the chymosin enzyme, chymosin can be produced without involving calves. Today it is estimated that 95 percent of American-style cheese is made with this form of fermented form of chymosin. There are, however, several styles of plant rennet that do not involve chymosin at all. The most popular plant-based coagulant or rennet comes from a thistle variety called Cynara cardunculus.

For more on rennet, see this article I wrote on page 2: https://www.cdr.wisc.edu/sites/default/files/pipelines/2012/pipeline_2012_vol24_03.pdf

Annatto:

Another fun fact I’ve learned during my time in the food world is that cheese varieties such as Cheddar get their signature orange color from a tropical plant extract called annatto. While the exact reasoning or origins behind the use of annatto are not clear to experts, we do know that annatto has been referenced in the cheese business for more than 200 years. Naturally, cheese is white or yellow in color. In the winter months when cows are not grazing cheese tends to have a pale white tint. In the summer, a yellow tint emerges thanks to the carotenoid in the grass that many cows consume while grazing. Therefore, some people believe that annatto was used as a colorant in order to create a uniform color for the cheese rather than allowing the color to shift with the seasons. Others believe that the colorant was added as a marketing tactic to differentiate cheese in one region from cheese in another. Regardless of the reason, the use of annatto has certainly caught on in the U.S.

            So what is annatto? Annatto is derived from the seed of the plant Bixa Orellana L.  The seeds of this plant are naturally covered in a reddish pigment which is what is extracted and used to create annatto. The amazing thing about annatto is that despite its strong color, it has no flavor, so adding it will not impact the flavor profile of the cheese. Annatto is also very stable so a brand new Cheddar and a seven year old Cheddar colored with annatto should have the exact same coloring assuming that the cheese has not sustained light damage or oxidation.

In terms of regulations, annatto is a natural product but because it is not naturally found in cheese it cannot be labeled as a natural colorant. In terms of safety, annatto has a long history of good food safety and has not been tied to significant allergen issues though in rare cases people do have an allergy to this colorant.

There’s a lot more to learn, so check out page 6 for an article I wrote on the topic: https://www.cdr.wisc.edu/sites/default/files/pipelines/2012/pipeline_2012_vol24_04.pdf

  

The Final Steps: Cutting, Heating, Draining and Salting

            After the addition of the colorant, starters and coagulants, the cheese is left to gel or set. Once the cheese reaches the proper texture, a cheesemaker will begin cutting the curd in order to break the now large coagulated mass of milk into tiny pieces called curds. This curd will then be heated.

During this process the curd will shrink and water will be expelled from the curd.  At the end of this process the curd will be separated from the liquid which is now called whey. At this point, the curd will go on to be further processed per its varsity’s requirements. So, what happens to the whey you might ask? 

                                                         Join us Friday to find out!

Have a question about cheese?  Let me know in the comments section and I will try to find an expert to answer your question. 

Want to learn more about cheesemaking?

·         Read an article: 

https://www.cdr.wisc.edu/pipeline

http://www.eatwisconsincheese.com/cheeses/how-cheese-is-made

·        

           Take a class:  

                  https://www.cdr.wisc.edu/shortcourses/world_of_cheese_17