Melted Cheese Frize [Photo Credit: Pittaya Sroilong]
Whether you are making cheese fries, grilled cheese sandwiches, quesadillas, baked cheese bites, or homemade mac and cheese, choosing the right type of cheese can make or break these comfort foods. The key to all of these dishes is cheese that produces an even and homogenous melt. Cheeses like Cheddar, Mozzarella, and Gruyere are used often. If you aren’t feeling adventurous, you could just memorize the names of these greatest hits. However, if you want to experiment and change the melty cheese game, you’re going to have to understand why these cheeses work.
Let’s first examine what happens to cheese as it melts. The interactions of casein (milk proteins) and calcium help define its solid structure. When solid, caseins are bound together in large branching porous protein networks that entrap milkfat and water. Calcium (as calcium phosphate) acts as a bridge to stabilize these networks. When you apply heat to a cheese, melting occurs in two stages. First, at around 90 ˚F, milkfat is released1. This is because hydrophobic (water-repulsive) interactions between casein molecules increase under heat2. These interactions force out water molecules and the space between casein molecules increases allowing milkfat, which melts at this temperature, to escape. If you’ve put cheese on a burger that’s being grilled, you may see little sweat beads of liquid form on the cheese in the early stages of melting. The second stage happens at about 40 to 90 degrees higher, at around 130 – 180˚F3. At this point, the casein proteins do not break down, but rather, the increased movement of the proteins, resulting from the heat, allows for the proteins to act more fluid-like and the cheese melts.
There are many factors that control melting and explain why melting temperatures vary by as much as 50 degrees. No one factor defines a cheese’s melting properties as these factors can interact.
Moisture and Fat
Cheese with higher moisture and fat content tends to have lower melting points. For example, high moisture cheeses like Mozzarella melt around 130 ˚F and low moisture cheeses like Swiss melt at 150 ˚F 2. First, as previously highlighted, the milkfat and water portion of the cheese react to heat at lower temperatures than the proteins. Accordingly, with more moisture and fat present in a cheese, greater proportions of the cheese are susceptible to melting at lower temperatures. When the fat becomes liquid, it can no long provide support for the protein networks. Secondly, increased moisture and fat means that the casein proteins are more spread out and the mesh size (gap between proteins) is larger. This means there are fewer connections (bound calcium bridges) between proteins networks making melting more likely to occur at lower temperatures.
You may not know the exact moisture and fat content of every cheese variety without looking at a label, but intuitively, softer cheeses have more moisture and fat. Additionally, younger cheeses generally have more moisture so they also tend to melt more uniformly and evenly.
Chesses typically melt homogenously and evenly around a pH of 5.0 – 5.44. This is related to the calcium bridges. At too high a pH (pH > 6), too much calcium is present as bound calcium phosphate and the protein is too tightly bound to melt. With lowered pH, the calcium phosphate bound to the casein is replaced by hydrogen (H+), allowing for more movement among proteins.2 At around a pH of 5.0 – 5.4, there is a sufficient number of calcium present as bridges to allow for melting. At too low a pH (pH < 4.6), too many calcium bridges are lost and proteins aggregate and are unable to flow and melt evenly.
Lastly as a caveat, the factors being highlighted are specific to rennet-set cheeses, and not acid-set cheeses. Acid-set cheeses like queso fresco, paneer, and ricotta are not generally used, as they don’t produce even melts4. This results from the way they were made. In cheese making, you have two options for separating the solid curds (primarily casein proteins) and the liquid whey; Use rennet (an enzyme derived from the intestines or baby goats and cows) or use an acid (like vinegar or lemon juice).
When they are free floating in liquid milk, casein proteins have a slightly different molecular structure than when they are in cheese. In milk, caseins stick together in small clusters (micelles) that have negative charges on their surface. Since negative charges repel each other, these micelles won’t combine. Adding acid to heated milk lowers the pH, which neutralizes the negative charges on the micelles; therefore the casein micelles can aggregate. In contrast, using rennet to set cheese is a more targeted approach. In this process, an enzyme contained in rennet called chymosin, selectively removes negatively charged portions of the casein micelles and allows the micelles to clump.
In an acid-set cheese, calcium bridges are never formed as a result of the acidic environment used to generate the cheese5. These cheeses are only held together in protein aggregates rather than protein networks with calcium bridges and don’t produce the even melt desired.
Rennet-set cheeses with high moisture and fat are the best cheeses for melting as they melt evenly and consistently.
But don’t fret if you still want to harness the flavor of other cheeses (especially older or drier cheeses)! You have options: Try using a cheese blend with a higher proportion of the better melting cheeses and a small proportion of the other cheeses. For example, this recipe uses a 1:4 ratio. Experiment! You now know the keys for melty cheese!
- Schloss, Andrew and David Joachim. “The Science of Melting Cheese” http://www.finecooking.com/item/64019/the-science-of-melting-cheese
- Johnson, Mark. “The Melt and Stretch of Cheese” https://www.cdr.wisc.edu/sites/default/files/pipelines/2000/pipeline_2000_vol12_01.pdf
- Mcgee, Harold. On Food and Cooking. 2004 “Cheese” (57 – 67).
- Tunick, Michael. The Science of Cheese. 2013 “Stretched Curd Cheeses, Alcohols, and Melting” (82 – 91).
- Sargento Food Service. “Cheese Melt Meter” http://www.sargentofoodservice.com/trends-innovation/cheese-melt-meter/
- Achitoff-Grey, Niki. “The Science of Melting Cheese” http://www.seriouseats.com/2015/08/the-science-of-melting-cheese.html