Fondue Chemistry

Fondue’s ingredients aren’t just there to taste good, they serve important purposes


Fondue is derived from the French verb “to melt” (fondre). If memory of my high school French class serves correct, fondue is the past tense of fondre. So I guess “melted” is a better translation. Enough of the etymology, let’s get to the science.

Fondue, at its core, is history’s first example of processed cheese. Fondue laid the groundwork for things like nacho cheese sauce; Velveeta’s distant great grandfather. Full disclosure time. This post was originally entitled “Processed Cheese”, but I figured “Fondue Chemistry” had better mass-appeal. So what does Fondue and processed cheese have in common? They utilize similar ingredients (sorta) and transform cheese into a form that melts superbly.



We’ve already discussed cheese melting quite a bit in a previous post. A few specifics come into play when making Fondue (and processed cheese for that matter):

  • Protein. Casein protein is the structure of cheese and its interactions are what dictate how cheese melts and how stable a Fondue will be.
  • Calcium and pH. As we’ve discussed at length before, there is a delicate balance of acidity and the resulting calcium-balance that influence how well a cheese will melt.
  • Moisture. The amount of water in the mix will help influence melting. There is a reason Fondue isn’t made using mizithra.
  • Fat. The amount of fat and how will its incorporated will dictate whether a Fondue is silky smooth or an oily mess.

Oily cheese

Melting cheese normally results in a grease ball, not the case for Fondue

These factors come into play when trying to make a gooey Fondue. While making Fondue greatly improves the melting properties of the cheese, starting with a good melter helps. The classics, Emmentaler and Gruyère, fit the bill. They’re of moderate acidity, moisture, and fat. Speaking of fat…



One of the most crucial steps of making a Fondue is forming a stable emulsion. An emulsion can be thought of as a dispersion of one substance in another. What’s special here is that those two substances don’t want to mix together. A classic example is trying to mix together oil and water. If you shake it really well, you may get them mixed for a bit, but they will eventually separate. To keep them mixed, you need the help of an emulsifier. Emulsifiers help keep the two parts of an emulsion together, preventing them from separating (or “breaking” as it’s called).


Emulsifiers help form stable emulsions

We run into this problem when making Fondue. If you take some Gruyère on its own and melt it, you’ll be left with an oily mess. We have to use some chemical trickery to keep the fat in the cheese (where it belongs).

Some vinaigrette recipes call for egg yolk since it contains emulsifying compounds. For our Fondue, we don’t add any emulsifiers per se, we add ingredients that help “activate” the emulsifiers that were already there all along.



Below is a brief list of common Fondue ingredients and their purposes. While each of them play a key role functionally or organoleptically, we’re going to focus on the wine and lemon juice. They are the secret to making a good Fondue.

CheeseStructure of the Fondue
White wineAdds moisture, acid, and provides emulsifying salts
CornstarchStabilizer, thickener
Lemon JuiceFlavor, assists with emulsifying, and adds acid
Garlic, nutmeg, kirschFlavorings

White wine seems like a natural ingredient for Fondue purely based on tradition and regionality. But more importantly, it contains tartaric acid. Tartaric acid functions as an emulsifying salt in our fondue. An emulsifying salt is an ingredient added to processed cheese to ensure they form a nice homogenous mixture that doesn’t get greasy and oily. Their name is a little misleading. They, themselves, aren’t emulsifiers. They alter the protein structure of the cheese and allow it to function as an emulsifying agent in our fondue.

You may recall that calcium is the “glue” that holds cheese together. Specifically, calcium cross-links the casein proteins in cheese. In their normal form, casein proteins don’t interact with fat much. The fat globules in normal cheese are just embedded in a protein network. Upon heating, that fat leaks out and forms an oily mess.

Emulsifying salts disrupt protein structure by binding calcium. By ripping the calcium glue out of casein proteins, emulsifying salts cause some of the caseins to break into little bits. These little protein chunks act as emulsifiers. They help the rest of the protein hold onto the fat. Now, when heated, the fat is less likely to oil off in excess.

Soluble casein

White wine turns protein into an emulsifier of sorts

Simply put, tartaric acid in wine (and citric acid in lemon juice) is changing the cheese protein structure allowing it to hold onto fat better. There is a little more to the story…



No doubt, the natural emulsifying salts in white wine and lemon juice are crucially important to forming a good Fondue. But there are a few other considerations that are important as well. By adding wine, you’re also adding quite a bit of water. Adding water increasing the overall moisture content and helps dilute the protein, leading to a smoother Fondue. The cornstarch further helps stabilize the emulsion and thicken the water phase of the Fondue.

Soluble casein Soluble casein

Fondue is an emulsion of cheese protein and fat
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While it may seem obvious, heating and melting the cheese during the Fondue-making process is important too. Heating and stirring helps reorganize the cheese structure — mixing the fat, protein, and moisture, leading to a silky-smooth Fondue. This, along with the fat being emulsified, creates Fondue’s unique texture.


All of the figures shown in this post are highly schematic and none of them are to scale.

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