Hot cheese is a sensual affair. Just consider the delight of watching soft, stretchy strands emerge from between the halves of a grilled cheese sandwich. Think of the anticipation of stirring a fresh egg and a pat of butter into the warm, cheese-filled center of a just-baked khachapuri...

There’s an allure to melted cheese that even the most discerning of cheese enthusiasts can’t deny, which is probably why fondue — a molten concoction of Alpine cheeses, wine, and spices served over a gentle flame with dippable accompaniments — is such an enduring favorite. While the version we know today likely differs from its earliest mentions in 800 BC[1], fondue’s beauty continues to lie in its suppleness.

But how does fondue — or any cheese sauce, for that matter — stay so fluid? On its own, melting cheese tends to rapidly morph into an oily, congealing blob. Though it may still taste good, cheese in this form certainly doesn’t hold the same visual appeal, nor (and perhaps more importantly) does it maintain the flowing viscosity necessary for use as a sauce or dip.

Recently struck with a longing to enjoy the pleasures of dipping salty tortilla chips into spicy cheese but wanting to go beyond the jars of mass-produced products that often fall short on flavor even if the ingredient list seems promising, I decided to learn more about the science of melted cheese. Specifically, I wanted to learn how to use sodium citrate. While béchamel is lovely and versatile and does politely welcome cheese into its velvety folds, isn’t the base I’m after when I’m craving a jalapeño-meets-sharp-cheddar flavor experience.

With a bag of sodium citrate in my cupboard and myriad cheeses in my refrigerator, I was ready to consult the experts and get to work.

First, a brief science lesson

To best appreciate sodium citrate’s function in a cheese sauce, we must first recognize the molecular structure of cheese and what happens to that structure as it melts.

It’s helpful to think of cheese as a three-part network consisting of fat, calcium, and casein protein. Calcium serves as an adhesive that binds together the proteins, but these proteins don’t otherwise interact with the fat.

“The fat globules in normal cheese are just embedded in a protein network,” says Pat Polowsky, the food scientist and dairy devotee behind the Cheese Science Toolkit[2]. The all-too-familiar oiliness when heating cheese is due to fat leaking out of the weakened protein structure. To avoid this, “We have to use some chemical trickery to keep the fat in the cheese.”

Polowsky notes that a good (read: non-oily) fondue is the result of a successful emulsion — a stable mixture of substances that normally do not like being combined. Just think, for example, about the behavior of oil and vinegar as you’re mixing up a vinaigrette, and how a nice dollop of Dijon mustard helps flavorfully bring the two together.

With fondue, that emulsifying trickery comes from the tartaric acid that is present in wine. A squeeze of lemon juice, often added anyway for its bright flavor, can further aid emulsion thanks to the citric acid. These acids function as emulsifying salts[3], which, as Polowsky explains, induce emulsification by disrupting the tightly knit protein structure and thus allowing for smoother, more cohesive melting.

Sodium citrate’s effect on cheese

Because sodium citrate is such a potent emulsifying salt, it’s a common ingredient in pasteurized process cheese products. Love it or hate it, process cheese is a carefully engineered food.

A 2006 study[4] by the American Dairy Science Association explored the effects of using sodium citrate in process cheese production. While considering variable factors like pH, moisture content, and temperature, the objectives of the study were to explore cooking times and differing concentrations of sodium citrate. The 14-page study concludes with a clear finding: “The concentration of [sodium citrate] used as an [emulsifying salt] in pasteurized process cheddar cheese manufacturing greatly affected the textural and melting properties, even when these process cheeses had a similar pH value.”

For those of us playing along at home, an especially useful tidbit is that researchers found that a small quantity of sodium citrate — in this case, a percentage of just 0.25 — proved insufficient in achieving the desired emulsification.

I found this helpful for my own endeavors because it’s not uncommon to see sodium citrate use referred to in terms of “a sprinkle” or “a pinch.” I’m all for trial and error in the kitchen, but quality cheese isn’t something I like to waste, and, unfortunately, my first few attempts at a sodium citrate cheese sauce were lackluster. I’ve turned out sauces that were too watery, too dense, or too grainy — though I blame my premature addition of pickled jalapeños on that last one.

After much reading and even more hands-on experimentation, I’ve arrived at what I find to be my ideal ratio of cheese to liquid to sodium citrate. It’s important to note that cheese sauce viscosity is a personal preference and I respect that some folks love an ultra-thin sauce while others prefer something closer to a loose paste. With this in mind, I offer you my technique. Please know that this recipe is extremely versatile, as you’ll read in the tips below.

Silky Sodium Citrate Cheese Sauce with Quick-Pickled Jalapeños

For the quick-pickled* jalapeños

• 2-3 fresh jalapeño peppers, thinly sliced

• 1 tbsp rice wine vinegar

• 1 scant tbsp sugar (I used coarse raw sugar; use whatever you have!)

• A pinch of flaky sea salt (a “pinch” is definitely okay here)

Combine sliced jalapeños with vinegar, sugar, and salt. Give them a good shake or stir and allow to stand at least 20 minutes before using. Keep refrigerated for up to a week.

*Please note that this method is intended for using your peppers within a few days; this is NOT a long-term food preservation method.

For the sodium citrate cheese sauce

*Note: Yes, I am calling for weighted measurements here, and I really insist upon this. Using a scale in the kitchen is not only more accurate, it’s faster, easier, and you’ll dirty less dishes. Scales can be had quite inexpensively, so I implore you to purchase if you don’t already have one! *

Thanks to the magic of sodium citrate, you can use any cheese or combination of cheeses you like. The two I’ve specified here were chosen because they pair well together (and with jalapeños), and should be relatively accessible. Speaking from personal experience, using 100 grams of cheese will yield enough sauce for 2 people to enjoy as a midday snack. Scaling up is easy: Simply maintain a ratio of 85% liquid and 4% sodium citrate, based on the total weight of your cheese.

• 50g aged white cheddar, grated

• 50g manchego, grated

• 85g water or beer of your choice

• 4g sodium citrate

• Cracked black pepper (to taste)

• Diced pickled jalapeños (to taste)

If it looks like this, keep whisking!

In a heavy-bottomed saucepan, slowly warm the liquid and whisk in the sodium citrate. Bring to a slight, gentle simmer, then whisk again to ensure the sodium citrate has dissolved completely.

Add your cheese gradually, continuing to whisk, until it’s all in the pan. Whisk steadily until all cheese has melted and you can lift the whisk without seeing bits of grated cheese still dangling from the wires.

This is the consistency we’re looking for

Be patient and trust the process. The cheese will fully incorporate into the liquid and you’ll achieve a glossy, smooth, spoon-coating texture, at which point you can add your black pepper and jalapeños — I like a lot of both!

Serve immediately, preferably with very good tortilla chips.

Additional cheese sauce tips:

● I have found that the sauce comes together more favorably in a ceramic saucepan than in stainless steel. Bonus: The ceramic is also much easier to clean.

● Some resources recommend using an immersion blender to coax your cheese into smoothness. You’re welcome to do this, but I’ve found that patience and even heat distribution make it very possible to create the sauce with a simple balloon whisk.

● Remember that the sauce will thicken as it cools. If it seems too runny for your liking right off the stove, just let it stand for a couple of minutes, stir again, and enjoy.

● Resist the urge to use pre-shredded cheese, which will contain anti-caking agents that may interfere with melting. Always just grate your own cheese; it tastes better anyway!

● Be sure that your cheese sauce has fully come together before introducing your add-ins.

● Since sodium citrate allows for a sauce with so few ingredients, flavors can really shine. Use quality cheese and don’t be afraid to get creative with your combinations and add-ins.

● Remember that the liquid ratio is adjustable! I’ve gone as far up as 95% and as low as 75%. Play around and find your own preference, just make sure your sodium citrate equates to 4% of the total weight of your cheese.

● Leftover cheese sauce can be refrigerated. It will solidify, but it reheats nicely.