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The Science of Melting Cheese

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By David Joachim and Andrew Schloss
From Fine Cooking #133

Gooey melted cheese is the key to every pot of creamy fondue and bowl of macaroni and cheese. Pizza and quesadillas are unthinkable without it. Yet some cheeses make terrible choices for these dishes, since they simply won’t melt well or can get unpleasantly stringy. Here’s what you need to know about finding the best melters so your next cheese-based dish turns out as creamy and delicious as possible.

What happens when cheese melts?
Two things happen. First, at about 90°F, the solid milk fat in the cheese begins to liquefy, the cheese softens, and beads of melted fat rise to the surface. As the cheese gets hotter, the bonds holding together the casein proteins (the principal proteins in cheese) break, and the cheese collapses into a thick fluid. This complete melting occurs at about 130°F for soft, high-moisture cheeses like mozzarella, around 150°F for aged, low-moisture cheeses like Cheddar and Swiss, and 180°F for hard, dry grating cheeses like Parmigiano-Reggiano.

Which cheeses are good melters, and why?
Several factors affect melting ability. One is moisture content. High-moisture cheeses, like mozzarella, cream cheese, and Brie, flow more easily than dry hard cheeses. In moist cheese, the proteins are loosely packed with lots of water interspersed between them, so they readily liquefy. But hard cheeses contain so little water that when they melt, they don’t completely liquefy. Take pizza, for example: Mozzarella melts into a liquid pool on top of the pizza, while specks of Parmigiano-Reggiano stay separate on the same pizza even after the Parmigiano melts.

The age of a cheese also affects how it melts. A glue of calcium atoms holds the casein molecules together. When cheese is heated, the calcium glue dissolves, and the casein molecules separate. In fresh, unaged cheese, the casein molecules are large and stretchy, and they tend to get tangled into ropes, which is why melted fresh mozzarella is stringy. During aging, the casein molecules get attacked by ripening enzymes, which break the casein into small pieces. When an aged cheese like Cheddar melts, these little pieces of casein flow without tangling, and the cheese melts smoothly.

Finally, factors like fat content and acidity play a role in how a cheese melts. Cheeses like Cheshire and Leicester are relatively high in fat, which makes them good melters. Cheeses that are high in acid, however, such as Swiss-style Emmentaler and Gruyère, become stringy when melted. And cheeses that are curded with acid rather than animal rennet–Indian paneer, Greek haloumi, Mexican queso blanco, Italian ricotta, most fresh goat cheeses, and most vegetarian cheeses–don’t melt at all. The acid dissolves the calcium glue that normally holds a cheese together. Unlike good melting cheeses, acid-curded cheeses are held together not by calcium, but simply by the casein proteins binding to one another in microscopic clumps. When acid-curded cheeses are heated, the protein bonds tighten, forcing out any water. As the water evaporates, there isn’t enough moisture left in the cheese to allow it to liquefy. Instead, the protein in the cheese solidifies further. That’s why queso blanco and paneer can be simmered or fried without melting, and why ricotta and fresh goat cheeses retain their shape in cooked ravioli and manicotti.

Dos and Don’ts for Smooth Melted Cheese

  • Do bring cheese to room temperature. This gives the cheese a head start toward reaching its melting point. It prevents a sudden temperature change that could cause the protein to coagulate too quickly and squeeze out the fat, resulting in clumps, a greasy texture, or both.
  • Do grate it. Finely grating the cheese creates more surface area, allowing heat to permeate quickly for even melting. Large or irregular chunks of cheese melt at different rates, can melt first on the outside and then overcook, or become clumpy or oily before the inside of the chunk starts to flow.
  • Do use low heat. Gradual temperature changes and relatively low temperatures overall will prevent the fat from separating out of melting cheese. Adding cheese to boiling liquid can cause the protein to coagulate too quickly, turning it clumpy or stringy and squeezing out the fat into a greasy mess. For best results, add cheese at the end of the cooking process so that it can just reach but not exceed its melting point.
  • Do add acid. When making fondues, sauces, and soups, adding white wine or lemon juice helps keep cheeses melted and smooth. The added acid in these ingredients binds to the calcium in the melted cheese, preventing it from cross-linking with the proteins and keeping them separate instead of clumped together. Wine and lemon juice also contribute some water to dilute the proteins and keep them flowing.
  • Do add starch. Flour or cornstarch is like insurance against clumping and stringiness in a cheese sauce. The starch coats the proteins and fats in the melted cheese, keeping the proteins from clumping and the fats from separating out.
  • Don’t stir too vigorously. Overstirring encourages the proteins to clump and could create a stringy or lumpy texture.
  • Don’t cool the cheese before serving. As it cools, melted cheese begins to get firm again and is more likely to clump.
  • Don’t use stringy cheese. Mozzarella will melt but won’t make a smooth and creamy sauce like a well-aged Cheddar or a high-moisture cream cheese. Save the mozzarella for pizza.

What’s Process Cheese?
Products such as Velveeta, Cheez Whiz, and some brands of American cheese are labeled as “process cheese food.” These are made with a blend of scraps from both aged and unaged cheeses that are melted, mixed with emulsifiers, pasteurized, and then molded into various shapes. According to the FDA, process cheese food must contain at least 51% natural aged cheese by weight. Such products melt well because the added acid and phosphates bond to the calcium in the cheese mixture, keeping the milk proteins separate and discouraging clumping. The phosphates also bond to both water and the casein proteins, keeping the milk proteins smooth and flowing, even when the cheese is heated past its melting point.

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Comments

  • Z-dog | 08/28/2017

    Very useful info. Covers a wide range of melted cheese based foods from pizza to fondue. Always wondered what made cheese fondues so tricky to properly prepare and now I can see the scientific basis.

  • HarrySchmincke | 06/13/2017

    Very interesting article. Made a good read while procrastinating from revising for my maths exam tomorrow. 10/10 would rather read this than revise.

  • Lindaship | 12/28/2016

    This is so helpful! I was really hoping to find out the best temperature to bake a pizza, so that the cheese is perfect. Sometimes it's tough when cooked.
    Any hints would be great!
    Thanks.

  • ChsBkr | 09/21/2016

    Great article...I'm amazed there isn't any comments and made an account just to tell the author thank you.

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