Melt and Stretch

How well a cheese will melt and stretch is dependent on its chemistry

Introduction

In homage to the Grilled Cheese Competition that happened this past Saturday, let’s talk about cheese melting! From grilled cheese to pizza to mozzarella sticks, many dishes wouldn’t be the same without the melty gooey goodness of cheese. Several factors influence how well a cheese will melt and stretch. The composition of the cheese, the acid level in the cheese, and the age of the cheese are some of the biggest factors. Like many of the posts on this site, we are creeping towards the “danger zone” of imprecision due to omission. This post isn’t an exhaustive foray into cheese melting chemistry and it leaves some things out. Think of it as a springboard for more learning!

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Cheese Composition

As we’ve discussed before, cheese is mostly protein, fat, and water. The casein protein makes up the structure of the cheese. Casein proteins form a 3-D mesh that has calcium acting as the “glue” holding the casein micelles together. Oftentimes this mesh is compared to a sponge. The holes in this casein “sponge” are embedded fat and water (or serum as its called).

Cheese structure

Simplified cheese structure diagram

Adding more fat or water to this structure can soften it and often means the cheese is prone to be a better melter. Higher moisture cheeses like young Gouda or Mozzarella are pretty good melting cheeses. Drier cheeses like aged Gouda and Parmigiano Reggiano won’t melt so well unless there is added moisture around. Similarly, higher fat cheeses like Havarti usually melt better than cheeses like non-fat mozzarella.

Moisture variations
Fat variations

Examples of how sometimes higher moisture and higher fat will lead to more melting.

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Melt and Stretch

Now that we’ve looked at cheese structure very close up, let’s look at it in a different way. You can think of cheese melt/stretch as those chains sliding past each other; all the while bonds between them are being broken and reformed. Imagine pulling the edges of those strands in the picture below.

casein strands

Simplified view of cheese protein strands being cross-linked by the calcium "glue"

Using this picture, two main things become apparent: (1) removing some of that calcium “glue” would allow those strands to stretch farther, and (2) if those strands got all chopped up (i.e. proteolysis), the stretch would be weak and perhaps non-existent. And by a stroke of fate, the next two sections address just that!

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Acid Level

Acid production is an important step for many different cheeses. Acid can be introduced to cheese in several ways. Cheesemakers will add acid directly or add cultures (bacteria) that produce acid. Some cheeses are made by coagulating milk with the direct addition of acid, like cottage cheese and chèvre. In cheeses like these, all that acid causes the casein micelles to attract to each other and aggregate together. All that attraction means the cheese won’t melt very well. It may soften upon heating, but not melt very much. In some cases, the bacterial cultures that cheese makers add are left to their own devices and produce a lot of acid. This will have a similar effect. Feta cheese for example, will only get soft when heated, it won’t melt or get gooey and stretchy.

Acid variations

The level of acid development often dictates how well a cheese will melt.
left - low acid, middle - moderate acid, right - High acid

On the other end of the spectrum, some cheeses have little-to-no acid. These cheeses won’t melt very well either. In this case, the cause is the calcium “glue” we mentioned earlier. Low acid cheeses will have lots of calcium in their structure. All that glue prevents cheese from melting well. Cheeses like Juustoleipa (i.e. bread cheese) and many Latin American cheeses fall into this category. They get soft upon heating, but still don’t flow and stretch all that much.

Acid variations

Acid is the "solvent" that dissolves calcium "glue"

In the middle, we have cheeses that have some acid. Acid dissolves the calcium “glue” from the casein mesh. An easy way to remember this is that acidic sodas dissolve the calcium in your teeth. With some of the calcium dissolved, this allows the protein structure to melt and stretch. Mozzarella, young Gouda, and other good melters fall into this category.

Acid variations

Acid development dictates how much calcium is removed from the casein matrix as well as how strongly the caseins will associate with each other

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Proteolysis

As we’ve seen, associations between those protein strands are crucial to getting the stretch we want. Just as important is the protein strands themselves. With time, those proteins could break down (i.e. proteolysis) and get all chopped up. Not having that intact network means stretch will be negatively affected. Often times there will be very little stretch and lots of free oil. The structure is so weak it can no longer be elastic or hold onto the embedded fat.

Proteolysis

Proteolysis is the breakdown of the protein structure
(those stretchy strands get all chopped up)

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Summary

With age, the chemistry of cheese changes. Acid is often produced and protein is breaking down. These two main factors (there are plenty of others we didn’t discuss here) have a tremendous impact on what will happen to the cheese as it melts and stretches.

Cheese Science

Click the picture!

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