Anyone who’s melted cheese for a sandwich knows that some types melt better than others, turning creamy without releasing fat. What factors account for the differences?
During our testing for Grown-Up Grilled Cheese Sandwiches, we found that younger cheeses almost always performed better than aged ones. This is partly because aged cheeses have less moisture, making them prone to clump. But our science editor told us that there are other more complicated factors at play as well, so we ran another test and controlled for moisture.
EXPERIMENT: We purchased Cabot Creamery cheddars aged for three, 16, and 24 months (all were sealed against evaporation during aging) and baked slices from each block on top of inverted metal cups that we preheated in a 175-degree oven until each slice had melted.
RESULTS: The three-month-old cheddar melted smoothly, evenly flowing down the cup’s sides. Meanwhile, the 16-month-old cheddar showed signs of clumping as it slid down the metal, and the 24-month-old cheese actually broke into two large pieces and never melted.
EXPLANATION: Moisture plays a part in how cheese melts, but the state of its protein—specifically, its network of casein protein—affects it most. In freshly made cheeses, casein proteins are in tightly wound clusters, allowing for little interaction with one another. As cheese ages, it goes through a process called proteolysis, in which bonds between individual casein molecules are “snipped,” allowing the clusters to unwind and bind with other casein molecules, forming a matrix. Early in this process, the matrix is flexible, allowing young cheeses to melt smoothly. With time, the proteins bond together tighter, forming a stronger network that requires more heat to melt and is less flexible when melted. This can result in more separated fat and clumps, as with our older samples.