Ask Milk Street: Why Is My Pasta Sauce so Watery?

In this week’s Ask Milk Street, we look into the best way to sauce your strands, examine the virtues of fresh and boxed pasta, and I share a cautionary tale.

Question: Why is my tomato sauce watery?

At its most elemental, tomato sauce is pulverized tomato; it's fibrous pulp and water. If you toss pasta directly into that, the pulp clumps up on top, and the water leaks onto the plate. Everybody’s aware by now that adding starchy pasta water helps sauce thicken and cling to the noodles (and simmering the sauce cooks off liquid), but starch alone does not make sauce cling.

The answer is fat. Starch is just the middle man between water and fat. It creates a "creamier" sauce by helping to suspend fat droplets within the liquid and preventing them from separating out.

The key to a tomato sauce that clings to your pasta is to capture that free-roaming tomato water by emulsifying it with some fat.

Which fat makes the clingiest tomato sauce?

I ran three trials of pasta sauce using our straightforward Toss-Your-Garlic Tomato Sauce as my base recipe model. In the first trial, I all but removed the fat from the recipe—I added scant oil (only enough to cook the garlic). In the next test I used the oil measurement indicated in the recipe (which is added in the beginning and to finish it at the end), and in the last test, I did the same, but I used butter to finish it at the end instead of the final splash of oil. Note that starchy pasta water was not added to any of these tests because it’s not used in the Toss-Your-Garlic Tomato Sauce.

In each test, I made the sauce and then added it to the cooked pasta over medium-low heat. Then I stirred it vigorously to coat the pasta. Depending on the test, I finished it with the selected fat and continued agitating it until the dish was finished.

The first plate, unsurprisingly, resulted in a sauce that didn’t hang onto the noodles well, with the tomato pieces slipping off and the sauce pooling at the bottom.

The second sauce, with its higher olive oil quotient, was slightly loose but with good cling.

The butter-finished sauce proved the clingiest, with absolutely no runoff.

Oil can work and adds richness, but it requires more elbow grease on your end to emulsify the two. Butter is best because it’s already a water-in-oil emulsion. You’re starting with something that’s primed for the job. The milk proteins in butter are amphiphilic—the structure has both water and fat-loving components—which create little bridges between the two. That’s why you’ll often see restaurant chefs finish pan sauces with butter. Butter brings sauces together. How beautiful.

So why use olive oil?

Butter isn’t necessarily the superior tomato sauce ingredient; your choice of fat depends on what you want the recipe to do. In this case, toss-your-garlic tomato sauce is about tasting subtle garlic flavor. Dairy tends to mute subtler, herbal flavors, while olive oil is generally considered lighter. If silkiness and cling is your priority, toss in butter. If you are worried about obscuring delicate flavors, go with olive oil and elbow grease.

Be sure to try our Raid-the-Pantry Pasta with Tomato Sauce, which is perfect as-is but can be used to test your new emulsification trick if needed.

Question: Does it matter… if I use boxed pasta instead of fresh?

Kind of.

It’s best not to think of them as completely identical ingredients. Dried, boxed pasta and fresh pasta are different creatures, and they have their own applications. I spoke with Domenica Marchetti, author of nine Italian cuisine cookbooks, on this topic here because this is a home cook FAQ.

Fresh and boxed pastas are not about a difference of quality, but more a difference of durability. Dried pastas are stronger and built to stand up to rigorous tossing with sauces, like with Roman Spaghetti Carbonara or Cacio e Pepe. Fresh pastas are usually much more delicate and can be rolled out extremely thinly, like with homemade ravioli or sheets of lasagna. These delicate sheets can be filled and gently boiled before being fished out of the water and lightly sauced, or with lasagna, layered with sauce and baked.

When it comes to boxed pasta, as you know, there's loads of basic stuff to choose from. Our recommendation is to look for bronze die-cut or bronze-cut pasta. This variety is different because the extruder used to shape the pasta leaves the surface of the dough rough and porous, as opposed to smooth and slippery.

Ask me how I know…that you absolutely have to salt pasta water

I’m getting married in a few days, but there is a universe where this marriage didn’t happen because of unsalted pasta water. When my partner and I met we cooked a lot, but it was always together. When we made pasta, I would ask if he salted the water already, and he’d say no—I didn’t ask why not. I would just take that as my salting cue.

When we moved in together, we started taking turns making dinner if one of us was particularly busy. One night, he made pasta with butter sauce and veggies. I took one bite and realized that I’d been salting his water because he didn’t know that salting is a must.

I realize that many folks need to cut down their salt intake. I have no issue with that, but I do take issue with folks who assume that salting the water is the same as salting the top of the finished dish. Salting the water seasons the inside of the noodles, imbuing the dough from within as it boils. This adds crucial flavor and also encourages the gluten network in the dough to tighten and firm up so you don’t get mushy pasta.

Did I mention he’s Italian-American? Anyway, he took my gentle questioning and constructive criticism well. He salts his water now—and the wedding is still on.

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Allie Chanthorn Reinmann

Allie Chantorn Reinmann is a Digital Staff Writer for Christopher Kimball’s Milk Street. She’s a Thai-American chef who earned her diploma for Pastry and Baking Arts at The Institute of Culinary Education and worked professionally for over a decade honing her craft in New York City at places like Balthazar, Bien Cuit, The Chocolate Room, Billy’s Bakery and Whole Foods. Allie took her know-how from the kitchen to the internet, writing about food full-time at Lifehacker for three years and starting her own YouTube channel, ThaiNYbites. You can find her whipping up baked goods for cafés around Brooklyn, building wedding cakes and trying her hand (feet?) at marathon running. She’s working on her debut cookbook and lives in Brooklyn, NY.